Although urolithiasis is a common problem in chelonians, most of the scientific literature on the subject is limited to case reports or case series in chelonians1–5 and other reptile species.6–9 In reptiles, clinical signs associated with urolithiasis include hyporexia, reduced fecal output, straining to urinate or defecate, reduced mentation, weight loss, and swelling of the hind limbs.1–10 Methods described for treatment of urolithiasis in chelonians include cloacoscopy-assisted cloacolith removal, cystotomy via plastronotomy, manual removal of cystoliths from the bladder with long forceps, and cystotomy or bladder marsupialization by a prefemoral approach.1,2,4,10–12,a
In chelonians, most uroliths are composed of urate,2,4,11,13,14 and 62 of 66 (93.9%) uroliths obtained from tortoises and 7 of 12 uroliths obtained from turtles that were analyzed at a large veterinary urolith center were composed of urate.15 Urate calculi have also been reported in many other species such as dogs,16,17 cats,18,19 Eurasian otters (Lutra lutra),20 North American river otters (Lontra canadiensis),21 a northern elephant seal (Mirounga angustirostris),22 a California sea lion (Zalophus californicus),22 bottlenose dolphins (Tursiops truncatus),23,24 and a blue-fronted Amazon parrot (Amazona aestiva).25 In chelonians, the pathophysiology of urate urolithiasis is postulated to be secondary to a variety of causes10 and likely differs from that for humans and dogs. However, the etiology of urate urolithiasis in chelonians has yet to be defined.
Although methods for treatment of urolithiasis have been described for a small number of chelonians,1,2,4,10–12 to our knowledge, a peer-reviewed retrospective study of the diagnosis and treatment of urolithiasis in client-owned chelonians has not been reported. The objectives of the study reported here were to calculate the prevalence of urolithiasis in client-owned chelonians examined at a veterinary teaching hospital and to describe the clinical signs, diagnosis, and treatment of urolithiasis in chelonians.
Materials and Methods
Case selection—The medical record database at the William R. Pritchard Veterinary Medical Teaching hospital was searched from January 1, 1987, through December 31, 2012, to identify and retrieve records of chelonians with urolithiasis. Keywords used for the search included turtle, tortoise, urolith, urolithiasis, cystic calculi, and bladder stone. Each of the retrieved medical records was reviewed by 1 investigator (KAK) to verify that the chelonian had urolithiasis. Urolithiasis was diagnosed on the basis of radiographic evidence in conjunction with confirmatory results from other diagnostic tests or direct visual observation of uroliths (n = 32), necropsy results in the absence of any other diagnostic test results (7), or CT results only (1). Confirmatory diagnostic tests included CT and coelomic ultrasonography, and direct visual observation included observing calculi in the urinary tract during surgery or necropsy. Chelonians were excluded from the study if they were not privately owned (eg, belonged to a zoological exhibit or other public or research entity) or urolithiasis was diagnosed on the basis of radiographic evidence without at least 1 additional confirmatory test result or visual observation of uroliths. Although cystoliths have been diagnosed in chelonians on the basis of radiographic evidence alone,10 some of the chelonians evaluated for the study had radiographic evidence of soft sludge in the bladder without discrete calculi; therefore, we selected more stringent inclusion criteria to ensure that the study population included only chelonians with a definitive diagnosis of urolithiasis.
Medical records review—For each chelonian, information extracted from the medical record included signalment, clinical signs, husbandry, dietary history, and results of all diagnostic tests or surgical procedures performed. The genus and species for each chelonian were extrapolated on the basis of the common name provided by the client. Sex was determined on the basis of secondary sexual characteristics for a given species or a history of laying eggs; the sex of juvenile patients was frequently undetermined. When age was unknown, the time that the animal was in the care of its current owner was recorded. Patient dietary information was classified into 1 of 3 categories as follows: comprehensive dietary history that included both the quantity and types of food offered, incomplete dietary history in which the type but not the quantity of food was available, or no dietary information available. Water availability was categorized as always, intermittent, or never or no information available. Plasma biochemical analyses and CBCs were performed at the veterinary teaching hospital in accordance with standard methods established by the clinical pathology laboratory. For chelonians, standard plasma biochemical variables reported included uric acid, calcium, phosphorus, glucose, cholesterol, BUN, ionized calcium, total protein, albumin, globulin, sodium, potassium, chloride, and bile acid concentrations and AST and CK activities. Standard CBC variables included RBC count, hemoglobin concentration, Hct, mean corpuscular volume, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, WBC count, and absolute concentrations of heterophils, eosinophils, basophils, lymphocytes, monocytes, and fibrinogen. For patients that had multiple CBCs and plasma biochemical analyses performed, only the results obtained closest to the time that urolithiasis was diagnosed were evaluated. When available, urinalysis was performed on urine samples obtained by ultrasound-guided cystocentesis or during cystotomy. Radiographic and CT images were reviewed by 1 investigator (KAK), and the number and location of calculi were recorded along with any other abnormalities that were identified.
Calculi retrieved from the urinary tract were analyzed at the G. V. Ling Stone Analysis Laboratory at the University of California-Davis. Uroliths were initially analyzed by the oil immersion method of optical crystallography with a polarized light microscopeb followed by Fourier-transform infrared spectrometry with a spectrometerc equipped with spectroscopy softwared and kidney stone library and analysis softwaree as described.26
Data analysis—The prevalence of urolithiasis in pet chelonians that were examined at the veterinary teaching hospital between 1987 and 2012 was calculated as the number of client-owned chelonians with urolithiasis divided by the total number of client-owned chelonians examined during that period. Summary statistics (mean, SD, median, and range) for CBC and plasma biochemical variables were calculated only for desert tortoises because they made up the majority (31/40 [77.5%]) of the study population. Descriptive data were provided for the other 9 chelonians.
Results
Prevalence of urolithiasis in client-owned chelonians—Between 1987 and 2012, 40 of 789 (5.1%) client-owned chelonians examined at the veterinary teaching hospital were confirmed to have urolithiasis. This equated to a mean of 1.54 chelonians with urolithiasis examined each year and a prevalence of 5.1 cases of urolithiasis/100 client-owned chelonians examined at the veterinary teaching hospital during the 26-year observation period.
Chelonians—The 40 chelonians with confirmed urolithiasis that met the inclusion criteria for the study included 31 (77.5%) desert tortoises (Gopherus agassizii), 3 (7.5%) African spurred tortoises (Centrochelys [Geochelone] sulcata), 2 (5%) red-eared sliders (Trachemys scripta elegans), 1 (2.5%) Hermann tortoise (Testudo hermanni), 1 yellow-bellied slider (Trachemys scripta scripta), and 1 Texas tortoise (Gopherus berlandieri); species was not recorded for 1 tortoise. The study population consisted of 19 (47.5%) males, 17 (42.5%) females, and 4 (10%) juveniles for which the sex could not be determined. When available, the mean age at the time of examination was 26.2 years (median, 24 years; range, 6 months to 100 years). The body weight at the time of examination was available for 38 of the 40 chelonians and ranged from 26 to 8,600 g (median, 3,875 g).
Thirty of 40 (75%) chelonians were examined because of a single problem, whereas the remaining 10 (25%) chelonians were examined because of multiple problems. The most common reason for examination was hyporexia (n = 10 chelonians) followed by constipation (5), swollen limbs (3), respiratory tract problems (3), lethargy (2), not laying eggs (2), cloacal prolapse (2), and collapse, toxicosis, soft shell, dog attack, being caught in a cord, wound, ulcerated feet, metal ingestion, diarrhea, nasal discharge, swollen eyes, and lack of urate production (1 each). Nine of 40 (22.5%) chelonians were referred to the veterinary teaching hospital after urolithiasis was diagnosed by another veterinarian, and 1 chelonian did not have any clinical signs and urolithiasis was diagnosed during routine annual physical examination.
Of the 40 study chelonians, 7 (17.5%) had a comprehensive dietary record available, 28 (70%) had an incomplete dietary record, and 5 (12.5%) had no dietary information. Review of the diets for which data were available revealed that most were species appropriate, and dietary histories included outdoor grazing opportunities with additional mixed leafy greens, vegetables, and fruits for the tortoises. The diets for 6 chelonians were deemed inappropriate; the diets for 5 desert tortoises were supplemented with commercially available monkey or dog food, and 1 adult red-eared slider was fed dog food exclusively. Nine of 40 (22.5%) chelonians were fed a dietary supplement intermittently; however, the products used were recorded for only 4. Of the 40 chelonians, water was available ad libitum for 21 (52.5%) and once or twice weekly for 2 (5%); the availability of water was not recorded for the remaining 17 (42.5%).
Physical examination results—During physical examination, only 10 of 40 (25%) chelonians had a solid coelomic mass palpable in the prefemoral fossa and abnormalities associated with the urogenital system were recorded for only 5 (12.5%). The most common abnormality identified during physical examination of the 40 chelonians was a change in mentation (n = 15) followed by nasal discharge (12), weakness (7), soft bones (5), wounds (5), edema (4), dehydration (3), hyperemic skin (3), evidence of previous plastronotomy (3), chemosis (3), pale mucous membranes (2), carapacial pyramiding (2), shell lesions (2), peeling skin (2), thickened skin (2), stomatitis (2), expiratory wheezes (2), ocular discharge (2), and cardiac arrhythmia, straining to defecate or urinate, yellow-colored urates, open-beak breathing, palpebral thickening, hyphema, and cataracts (1 each).
Diagnostic test results—Plasma biochemical and CBC results were available and summarized for 25 desert tortoises (Table 1). Results were compared with referent values obtained from a database for desert tortoises maintained by the International Species Information System.f Results were not available for all variables for all tortoises; therefore, the number of tortoises that contributed to the summary statistics varied among variables. For example, electrolyte concentrations were determined as part of the biochemical analysis for only 11 of the 25 desert tortoises. Hematologic abnormalities identified in those tortoises included hemoconcentration (n = 3), leukopenia (2), leukocytosis (9), absolute azurophilia (4), and absolute eosinophilia or basophilia (2). Review of plasma biochemical analyses revealed that 1 tortoise had severe hypocalcemia and hyperphosphatemia as a result of nutritional hyperparathyroidism. Four tortoises had AST activity increased from the upper referent value, and 4 tortoises had CK activity increased from the upper referent value, 2 of which also had abnormally increased AST activity. One tortoise had hyperuricemia and 2 tortoises had BUN concentrations increased from the upper referent value. Four tortoises had hypernatremia, 1 tortoise had hyperkalemia, and 1 tortoise had hyperchloremia.
Summary statistics for CBC and plasma biochemical variables for 25 client-owned desert tortoises (Gopherus agassizii) with urolithiasis that were examined at a veterinary teaching hospital between 1987 and 2012.
| Referent values* | ||||||
|---|---|---|---|---|---|---|
| Variable | No. of tortoises | Mean ± SD | Median (range) | Range | SD | No. of tortoises |
| RBC count (× 106 cells/μL) | 13 | 0.65 ± 0.15 | 0.65 (0.43–0.98) | 0.12–26 | 6.81 | 14 |
| Hemoglobin (g/dL) | 14 | 7.74 ± 1.19 | 7.5 (6.2–10.4) | 4.0–9.8 | 1.9 | 7 |
| Hct (%) | 24 | 31.54 ± 9.89 | 31 (18–60.5) | 10–41 | 7.3 | 39 |
| Mean corpuscular volume (fL) | 13 | 526.8 ± 179.45 | 523.3 (270.4–746.7) | 267.9–2,250 | 505.7 | 13 |
| Mean corpuscular hemoglobin (pg) | 13 | 123.62 ± 20.5 | 122.5 (77.6–163) | 79.7–708.3 | 225.3 | 7 |
| Mean corpuscular hemoglobin concentration (g/dL) | 14 | 24.7 ± 4.72 | 27.35 (14.6–28.9) | 18–34 | 5.4 | 7 |
| WBC count (× 103 cells/μL) | 24 | 5.78 ± 2.75 | 5.55 (1–11.4) | 2.4–12 | 2.53 | 35 |
| Heterophil count (× 103 cells/μL) | 24 | 2.47 ± 1.62 | 2.1 (0.23–6.79) | 0.1–8.29 | 2.18 | 33 |
| Lymphocyte count (× 103 cells/μL) | 24 | 0.99 ± 0.73 | 0.91 (0.09–2.81) | 0.61–6.08 | 1.16 | 33 |
| Monocyte count (× 103 cells/μL) | 24 | 0.28 ± 0.38 | 0.2 (0–1.54) | 0.03–1.68 | 0.4 | 16 |
| Eosinophil count (× 103 cells/μL) | 24 | 0.46 ± 0.92 | 0.1 (0–4.56) | 0.08–1.96 | 0.5 | 19 |
| Basophil count (× 103 cells/μL) | 24 | 0.94 ± 0.65 | 0.84 (0–2.75) | 0.03–2.42 | 0.679 | 32 |
| Azurophil count (× 103 cells/μL) | 24 | 0.39 ± 0.57 | 0.14 (0–2.23) | 0–0.76 | 0.25 | 9 |
| Fibrinogen (mg/dL) | 22 | 163.64 ± 126.3 | 100 (100–500) | — | — | — |
| Uric acid (mg/dL) | 24 | 5.48 ± 3.77 | 4.7 (1.5–21.6) | 0.6–12.9 | 2.7 | 29 |
| Calcium (mg/dL) | 24 | 12.24 ± 3.55 | 12 (2.8–21.9) | 6.0–36.6 | 6.2 | 33 |
| Phosphorus (mg/dL) | 24 | 3.36 ± 3.85 | 2.4 (1.1–21.2) | 1.2–13.5 | 3.0 | 31 |
| Glucose (mg/dL) | 24 | 86.96 ± 29.89 | 84 (48–175) | 33–175 | 37 | 28 |
| Total protein (g/dL) | 24 | 4.47 ± 1.09 | 4.5 (1.9–6.6) | 1.2–7.7 | 1.4 | 33 |
| Albumin (g/dL) | 20 | 1.74 ± 0.55 | 1.7 (0.9–2.9) | 0.4–3.0 | 0.6 | 24 |
| Globulin (g/dL) | 20 | 2.75 ± 0.73 | 2.7 (1–4.1) | 1.2–4.7 | 0.8 | 24 |
| AST (U/L) | 24 | 178.88 ± 210.2 | 88 (34–593) | 24–315 | 66 | 30 |
| CK (U/L) | 24 | 9,335.26 ± 21,289.3 | 2,422 (83–95,790) | 52–6,945 | 1,783 | 25 |
| Cholesterol (mg/dL) | 20 | 156.9 ± 140.16 | 120 (40–727) | 27–476 | 145 | 17 |
| BUN (mg/dL) | 18 | 15.78 ± 16.4 | 10 (2–57) | 0–41 | 10 | 22 |
| Ionized calcium (mmol/L) | 5 | 1.49 ± 0.55 | 1.74 (0.47–2.02) | — | — | — |
| Sodium (mmol/L) | 11 | 144 ± 8.11 | 140 (134–156) | 127–150 | 6 | 26 |
| Potassium (mmol/L) | 11 | 4.82 ± 1.16 | 4.8 (3.3–7.5) | 2.2–6.6 | 1.1 | 18 |
| Chloride (mmol/L) | 11 | 111.2 ± 10.5 | 110.5 (98–134) | 97–121 | 7 | 19 |
| Bile acids (μmol/L) | 2 | 0.5 ± 0.5 | 0.5 (0–1) | — | — | — |
Results were not available for all variables for all tortoises.
Referent values were obtained from a database for desert tortoises maintained by the International Species Information System.
— = Not available.
A CBC and plasma biochemical analysis were performed in 1 African spurred tortoise and 1 tortoise of unknown species, and a plasma biochemical analysis and determination of PCV were performed in another African spurred tortoise and 1 Texas tortoise. One of the African spurred tortoises had a cloacolith that caused both a urinary and fecal obstruction and was clinically dehydrated and hyperuricemic (uric acid concentration, 12.1 mg/dL; referent interval,27 2.1 to 10.5 mg/dL). The hematologic and biochemical results for the other 3 tortoises were unremarkable.
Urinalysis was performed for 3 desert tortoises; urine samples for 2 of those tortoises were obtained by ultrasound-guided cystocentesis, whereas the urine sample for the other tortoise was obtained during cystotomy. An additional tortoise that had cystocentesis performed only had the urine evaluated grossly and was recorded as pale yellow in color with no additional information. Urine specific gravity for those 3 tortoises ranged from 1.004 to 1.009 (referent interval,28,29 1.003 to 1.014). The urinary pH (referent interval,28 8.0 to 8.5) was 8 for 2 tortoises and 5 for a male tortoise with an obstructive cloacolith. None of the 3 tortoises had glucosuria or ketonuria. The urine sample obtained during cystotomy contained trace protein and 1+ hemoprotein. Analysis of the urine sediment revealed an absence of RBCs, WBCs, urinary casts, bacteria, lipids, and sperm for all 3 tortoises; however, a few transitional cells were observed in the urine sediment for 2 of the tortoises, and 2 tortoises had ammonium biurate crystalluria.
Radiographs were available for review for 19 of the 40 (47.5%) chelonians. Radiographic views commonly obtained included a standard dorsoventral view and horizontal-beam lateral and cranial-caudal views. When calculi were visible, they typically had a radiopaque laminar appearance and were generally located in the midcaudal region of the coelom and best visualized on dorsoventral images (Figure 1). The number of calculi in the urinary tract region visualized on radiographic images ranged from 0 to 4 (median, 1 calculus). One chelonian did not have radiographic evidence of urolithiasis despite the observation of numerous small, rough cystoliths associated with a ruptured urinary bladder during necropsy. Twelve chelonians had 1 urolith visualized during review of radiographic images, and the urolith was located in the left lobe of the bladder (n = 7), right lobe of the bladder (2), accessory lobe of the bladder (1), or in the cloaca (2). Six chelonians had multiple calculi, all of which were located in the bladder. Other abnormalities observed during review of radiographic images included long bone fractures (n = 3 chelonians), diffuse osteopenia (3), gastrointestinal dilatation with gas (6), gravel in the gastrointestinal tract (1), pulmonary changes suggestive of pneumonia (1), and retained calcified eggs (1).
Dorsoventral radiographic image of a > 13-year-old male desert tortoise (Gopherus agassizii) that was obtained as part of a routine annual physical examination. Notice a large round radiopaque lamellar structure (arrows) characteristic of a urate urolith in the left middle region of the coelom.
Citation: Journal of the American Veterinary Medical Association 247, 6; 10.2460/javma.247.6.650
Dorsoventral radiographic image of a > 13-year-old male desert tortoise (Gopherus agassizii) that was obtained as part of a routine annual physical examination. Notice a large round radiopaque lamellar structure (arrows) characteristic of a urate urolith in the left middle region of the coelom.
Citation: Journal of the American Veterinary Medical Association 247, 6; 10.2460/javma.247.6.650
Dorsoventral radiographic image of a > 13-year-old male desert tortoise (Gopherus agassizii) that was obtained as part of a routine annual physical examination. Notice a large round radiopaque lamellar structure (arrows) characteristic of a urate urolith in the left middle region of the coelom.
Citation: Journal of the American Veterinary Medical Association 247, 6; 10.2460/javma.247.6.650
Thirteen of the 40 (32.5%) chelonians underwent CT of the coelom, and uroliths were identified in all 13 (Figure 2). Both radiographic and CT images were available for review for 4 chelonians, and the number and location of uroliths visualized on the radiographic images were in agreement with those visualized on the CT images. For 2 of those chelonians, evaluation of the CT images provided additional information that was not apparent during review of the radiographic images; noncalcified eggs were identified in one, and a large, hypodense liver suggestive of hepatic lipidosis was identified in the other. For the 9 chelonians that did not have radiographic images available for review, abnormalities identified during review of the CT images included pulmonary infiltrates (n = 2), soft tissue coelomic masses (2), mineralized eggs (1), great vessel mineralization (1), and coelomic fluid (1).
Cross-sectional CT image of the tortoise in Figure 1 obtained at the level of the urinary bladder and colon. Notice a radiopaque lamellar structure characteristic of a urate urolith in the left ventral region of the coelom.
Citation: Journal of the American Veterinary Medical Association 247, 6; 10.2460/javma.247.6.650
Cross-sectional CT image of the tortoise in Figure 1 obtained at the level of the urinary bladder and colon. Notice a radiopaque lamellar structure characteristic of a urate urolith in the left ventral region of the coelom.
Citation: Journal of the American Veterinary Medical Association 247, 6; 10.2460/javma.247.6.650
Cross-sectional CT image of the tortoise in Figure 1 obtained at the level of the urinary bladder and colon. Notice a radiopaque lamellar structure characteristic of a urate urolith in the left ventral region of the coelom.
Citation: Journal of the American Veterinary Medical Association 247, 6; 10.2460/javma.247.6.650
Ultrasonographic evaluation of the coelomic cavity was performed during the initial examination for 4 desert tortoises. Ultrasonography was used to facilitate cystocentesis and diagnostic coelomocentesis in 1 tortoise and to facilitate cystocentesis and characterize the stage of ovarian development to assess whether ovariosalpingectomy could be performed in conjunction with the cystotomy for cystolith removal in another. In the remaining tortoises, ultrasound was performed solely to facilitate cystocentesis in one and to evaluate the coelom for a cause of hematochezia in another. Three tortoises also had CT of the coelom performed, and review of the ultrasonographic findings did not reveal any information that was not revealed during review of the CT images.
Treatment—Seventeen of 40 (43.6%) chelonians with urolithiasis underwent surgery to remove the uroliths. The most common surgical approach was cystotomy via plastronotomy (n = 12) followed by holmium:yttrium-aluminum-garnet laser lithotripsy via a prefemoral fossa approach to the urinary bladder (3) and endoscopic-assisted manual digital removal of cloacoliths through the cloaca (2). During surgery, 6 of the 17 chelonians had a pharyngostomy tube placed to facilitate administration of postoperative medications and nutritional support. All surgeries were performed by faculty clinicians or residents undergoing exotic animal training under the direct supervision of a faculty clinician. Surgical intervention was recommended for all study chelonians, but not all clients chose to pursue surgical intervention. The decision to perform either cystotomy or lithotripsy for urolith removal was made on the basis of the attending clinician's preference.
Five of the chelonians that underwent surgery developed postoperative complications. Four years after cystotomy via plastronotomy was performed, a desert tortoise was examined because of a partially nonadhered epoxy patch and lack of plastronotomy patch healing. That tortoise had complete loss of the keratin and bone in the plastron flap created during the cystotomy; however, the underlying tissue was thickened and CT evaluation revealed that there was no communication with the coelomic cavity. It was successfully treated by placement of a new epoxy patch. Two months after cystotomy via plastronotomy, another desert tortoise was examined because it had not urinated in 1 month. Physical examination revealed abnormally increased respiratory effort and a palpable coelomic fluid wave. Ultrasonographic evaluation of the coelom revealed a severely distended bladder, and removal of urine by cystocentesis resulted in an improvement in respiratory effort. The tortoise was anesthetized, and attempts to catheterize the urinary bladder were unsuccessful. The patient died after anesthesia was discontinued, and severe bladder distension and bladder wall mucinosis were observed during necropsy. A third desert tortoise died acutely 4 days after cystotomy via plastronotomy was performed, and the owner did not permit performance of a necropsy. A fourth desert tortoise died 3 days after lithotripsy, and necropsy results were indicative of acute cystitis with evidence of disseminated intravascular coagulation. A fifth desert tortoise was euthanized 2 days after initial examination following repeated unsuccessful manual attempts to remove a cloacolith via cloacoscopy, and the owner did not permit performance of a necropsy. Thus, 4 of 17 chelonians died following surgery for urolith removal (2 following plastronotomy, 1 following lithotripsy, and 1 following attempted manual removal of a cloacolith).
Necropsy results—Twenty-two of the 40 (55%) chelonians were discharged from the hospital alive, and long-term follow-up information was unavailable for most of those patients except for those that were examined because of postoperative complications. Necropsy was performed on 18 of the 40 (45%) study chelonians. The decision to euthanize or the cause of death was associated with urolithiasis or complications following surgery for urolith removal in 9 of those chelonians. Two chelonians (a 51-year-old female desert tortoise and a 57-year-old female desert tortoise) died of postoperative complications following surgery for urolith removal as described. A female desert tortoise that was > 60 years old had cystoliths and was euthanized because of a uterine prolapse. A 2-year-old male African spurred tortoise had cystoliths and was euthanized because of a cloacal prolapse. Two other desert tortoises with cystoliths (a > 20-year-old female and a > 50-year-old male) died secondary to complications from a ruptured urinary bladder and had evidence of coelomitis with or without gastrointestinal ileus. A > 36-year-old male desert tortoise with a cloacolith was euthanized because of gastrointestinal obstruction and ileus. A 6-month-old female Hermann tortoise with a cloacolith died secondary to chronic fecal impaction and septic coelomitis caused by a colonic perforation and also had a thickened bladder wall and nutritional secondary hyperparathyroidism. A female yellow-bellied slider of unknown age was euthanized because of deteriorating condition at home and found to have bilateral obstructive ureteroliths.
Of the 18 chelonians on which necropsies were performed, 14 had cystoliths, 2 had cloacoliths, 2 had ureteroliths, and 2 had no uroliths identified but died or were euthanized after surgical removal of cystoliths. One chelonian with cystoliths also had ureteroliths, and another with cystoliths also had a cloacolith. Other lesions identified in the urinary tracts of the 18 chelonians that were necropsied included a thickened (n = 3) or necrotic (1) bladder wall, tear in the bladder wall (2), and severe bladder distension and bladder wall mucinosis (1), renal gout (1), membranous glomerulopathy and interstitial fibrosis (1), glomerulonephritis and interstitial fibrosis (1), and interstitial fibrosis with mineralization (1). Abnormalities identified during necropsy that were not associated with the urinary tract included hepatic lipidosis (n = 18), endoparasitism (3), pneumonic lesions (3), generalized ileus (2), colonic obstruction secondary to calculi (2), gastric ulceration (1), cecal foreign body (1), stomatitis (1), and sand impaction (1). Three chelonians had lesions consistent with nutritional secondary hyperparathyroidism. Two chelonians had neoplastic lesions; 1 had squamous cell carcinoma of the plastron and adjacent fat pads, and the other had metastatic thyroid carcinoma.
Urolith composition—Uroliths from 13 chelonians were submitted for analysis. Those uroliths were obtained from the bladder (n = 12) or cloaca (1) during surgery (9) or necropsy (2) or by some unrecorded method (2). All uroliths were composed of 100% urate.
Discussion
To our knowledge, the present study was the first to determine the prevalence of urolithiasis in a population of chelonians and the first to evaluate a population of client-owned chelonians with confirmed urolithiasis. The mean prevalence of urolithiasis (5.1 cases/100 client-owned chelonians examined) during the 26-year observation period of the present study suggested that the disease is fairly common in client-owned chelonians examined at our institution. In a survey30 of necropsy results for tortoises that died in captivity, the prevalence of urolithiasis was 4.2% (6/144). The prevalence of urolithiasis calculated for the chelonians of the present study may be an underestimate of the true prevalence because of the strict inclusion criteria used for enrollment of study subjects or may be specific to our region or hospital and may not be valid for populations in other geographic regions or comprised of different chelonian species.
The majority (31/40 [77.5%]) of chelonians evaluated in the present study were desert tortoises, and this likely represents a regional bias. Urate urolithiasis has been reported in both free-ranging and client-owned desert tortoises.4,10,11,14 African spurred tortoise was the second most common species evaluated in the present study, and urate urolithiasis has likewise been reported in that species.1,2 In Europe, the most common chelonian species affected by urolithiasis belonged to the genera Testudo and Geochelone, which further substantiates regional differences in species that develop urolithiasis.13,30 Interestingly, 3 aquatic turtles with urolithiasis were included in the present study. To our knowledge, prior to this study, urolithiasis had been described in only 2 aquatic chelonians,3,5 and uroliths were not described in a large retrospective study31 of necropsy findings in aquatic chelonians. Cumulatively, these findings indicate that, although several species are overrepresented in the literature, many chelonian species can develop urolithiasis.
All of the calculi analyzed in the present study were composed of 100% urate. Although the etiology of urolithiasis in chelonians has yet to be identified, the pathophysiology of urate urolithiasis in chelonians is postulated to develop secondary to a variety of causes such as chronic dehydration, vitamin A and D deficiencies, and excessive intake of dietary calcium, protein, or oxalates.10 In mammalian species, causes of urate urolithiasis include hypocitraturia,24 metabolic aberrancies associated with portosystemic shunts,19 and mutations in the SLC2A9 gene that result in hyperuricemia and hyperuricosuria.17 To our knowledge, many of these etiologies have not been investigated in chelonians with urolithiasis; however, chelonians process nitrogenous wastes differently than do mammals.
In the present study, most of the chelonians were terrestrial species that are uricotelic, which means they excrete nitrogenous wastes in the form of uric acid.32 Uric acid is the end product of nitrogen metabolism through a series of enzymatic reactions that involve xanthine oxidase.33 Endogenous uric acid production results from de novo purine synthesis and tissue catabolism. Exogenous uric acid production is dependent on diet and is particularly high when the diet is rich in animal protein.33 Most terrestrial chelonians typically have a low-protein diet and should not have excessive exogenous protein metabolism unless they are fed inappropriate diets, which can sometimes happen with captive tortoises. The dietary history for 33 of the 40 (82.5%) chelonians in the present study was incomplete or unavailable, so although few diet abnormalities were identified in the study population, it is possible that some went undetected because of incomplete dietary histories. Clinicians should ensure that comprehensive dietary histories are obtained for chelonians to aid in the elucidation of the role, if any, that diet has in the development of urolithiasis.
In chelonians, uric acid is actively secreted by the proximal tubules of the kidneys and excreted in the urine.32 The form in which uric acid is excreted is dependent on urine pH. When urine pH is < 5, uric acid is present in the urine, whereas when urine pH is > 6.5, most of the uric acid is excreted as urate or urate salts.33 Tortoises, like other herbivores, tend to have alkaline urine,28,29 which favors the physiologic formation of urate. Results of the present study and other case reports and studies11,13–15 indicate that a high percentage of uroliths obtained from chelonians are composed of urate; however, uroliths should not be confused with the normal urate material physiologically excreted by terrestrial chelonians. Also, it is important to note that uroliths of mixed composition or composed of struvite, calcium phosphate, oxalate, and calcium carbonate have also been described in chelonians.3,5,13,15,34
Unlike mammals, urine is modified in the lower urinary tract of chelonians. Urine that passes through the ureters into the cloaca can flow retrograde into the bladder or colon, and urine in the bladder can flow retrograde into the colon. The epithelium of both the bladder and colon can absorb water, which results in urine concentration.32,35 Free-ranging desert tortoises retain urate precipitates in the bladder until rainfall stimulates bladder emptying followed by imbibition of a large volume of water.35 Thus, chronic dehydration, chronic overheating, or lack of a suitable water source might cause an increase in water absorption from the bladder and colon, which leads to further supersaturation and concentration of urate excreta in the bladder and might be a predisposing factor for urolith formation. Twenty-one of 40 (52.5%) chelonians of the present study had free access to water; however, 2 (5%) had only intermittent access to water, and water availability was not indicated in the medical records for 17 (42.5%). Although 34 of the 40 (85%) chelonians were considered desert species (desert tortoises and African spurred tortoises), those species still require water, particularly in captive situations where a humid burrow is often not provided. In addition to humidity, a burrow provides terrestrial desert chelonians with a cool area to escape hot daytime temperatures. Currently, it is unknown how restricted water access and possible chronic overheating affects the incidence of urolithiasis in client-owned chelonians in California. Clinicians are encouraged to obtain information about water availability, temperature and temperature gradient monitoring, and the availability of burrows in outdoor enclosures when acquiring histories for chelonians.
Many of the chelonians of the present study were examined for reasons unrelated to the urogenital system. Although most cats with urolithiasis are examined because of urination abnormalities,19 only 1 of the tortoises of the present study was examined because of abnormal urination. Owners typically do not observe chelonians urinate because tortoises are kept outside when the weather is appropriate, and free-ranging desert tortoises may only urinate during the rainy season and have infrequent urination patterns, compared with those of domestic mammals.35 Other clinical signs of the urogenital tract (cloacal prolapse, constipation, and egg retention) that are associated with urolithiasis1,2,10 were reported in only 5 of the 40 (12.5%) chelonians of the present study. In this study, only 1 chelonian without a history of clinical signs had urolithiasis diagnosed during a routine annual physical examination, which contrasted with results of another study11 in which urolithiasis was diagnosed during routine physical examinations of all 100 tortoises evaluated. In that study,11 1 veterinarian examined all the tortoises at a primary care facility; however, the chelonians of the present study were examined by various veterinarians and most were referred to a tertiary veterinary care facility. Therefore, all chelonians should have a routine annual examination that includes diagnostic imaging to screen for urolithiasis so that the disease can be identified and treated before it becomes an emergency situation. Furthermore, clinicians should be aware that, unlike dogs and cats, chelonians with urolithiasis are often examined for reasons unrelated to the urogenital system.
Few chelonians in the present study had physical examination abnormalities specifically related to urolithiasis. Most had musculoskeletal, respiratory, or miscellaneous abnormalities. Although diagnosis of urolithiasis via digital palpation of a hard structure in the prefemoral fossa has been described,10 only 10 of 40 (25%) chelonians in the present study had a urolith that was palpable through the prefemoral fossa. The surprisingly low percentage of chelonians with a palpable calculus in the prefemoral fossa in this study might be the result of poor record keeping, lack of prefemoral palpation during physical examination because of patient size, or lack of sensitivity of this physical examination variable. Regardless, the results of the present study suggested that the lack of physical examination abnormalities related to the urogenital tract or a palpable mass in the prefemoral fossa of chelonians should not preclude urolithiasis as a differential diagnosis.
The chelonians of the present study had few hematologic and biochemical abnormalities, which contrasted with the results of another study14 in which free-ranging desert tortoises that died because of urate urolithiasis had substantially abnormal BUN and uric acid concentrations. In the present study, only 3 desert tortoises had hyperuricemia or abnormally increased BUN concentrations. Failure to identify a trend for hematologic or biochemical abnormalities in chelonians with urolithiasis might be associated with the low number of study chelonians that had a CBC or plasma biochemical analysis performed. Also, in chelonians, clinically normal hematologic and biochemical variables vary greatly on the basis of season, sex, sexual maturity, nutrition, environment, and husbandry, which makes clinical interpretation of the data from this retrospective study difficult. Because appropriate reference intervals for hematologic and biochemical variables have yet to be established for captive desert tortoises, we used values obtained from the International Species Information System database as referents in the present study; however, the limitations of those values (obtained by use of multiple methodologies, without confirmation of systemic health) should be considered.
In nonchelonian species with urolithiasis, urinalysis frequently reveals hematuria, pyuria, bacteriuria, hypocitraturia, crystalluria, and pH abnormalities.16,18,19,24 Urinalysis was performed for only 3 tortoises in the present study. Microscopic evidence of blood was detected in the urine of only 1 tortoise, and that urine sample was obtained during surgery and might have been contaminated with blood. The urine pH fell within the expected alkaline range for 2 of the 3 tortoises; however, 1 tortoise had a urine pH of 5.0, which might have been a consequence of prolonged anorexia29 or acid-base aberrations associated with obstruction of the lower urinary tract. Two tortoises had crystalluria, which is a common finding in the urine of healthy tortoises.28,29 The paucity of urinalysis results for the tortoises of the present study and the lack of clinically normal urinalysis values for chelonians limit the value of urinalysis for diagnosis of urolithiasis in chelonian species until further information is obtained.
Urate uroliths are not always visible on radiographic images. Uroliths were visible on radiographic images of 143 of 159 (90%) cats with urate urolithiasis; however, many of those cats had uroliths that contained both urate and struvite or calcium oxalate.19 In chelonians, urate uroliths have a thick laminar appearance on radiographic images, and this laminar appearance is presumed to be caused by the repeated deposition of supersaturated crystalline material on the urolith.10 Of the 19 chelonians for which radiographic images were available for review in the present study, 18 had uroliths that were radiographically visible. For the chelonians that had only 1 urolith identified radiographically (n = 12), that urolith was generally located in the left lobe of the bladder (7), a finding that was in agreement with the results of another study.11 Chelonian species typically have a bilobed urinary bladder36 and an asymmetric liver in which the right hepatic lobe is generally larger than the left hepatic lobe. It is hypothesized that the large right hepatic lobe decreases the space available for calculus formation in the right lobe of the bladder.36
Seventeen of the 40 chelonians of the present study underwent surgery for urolith removal, 5 developed postoperative complications, and 4 of those died or were euthanized. The most common surgical procedure performed for urolith removal in the present study and other studies2,4,10,11 was cystotomy via plastronotomy. Three of the 12 tortoises that underwent that procedure developed complications, and 2 subsequently died. The cause of bladder wall mucinosis in the tortoise that died 2 months after the plastronotomy was unknown and might have been secondary to overactive granular cells in the bladder epithelium that secrete mucus to protect the epithelium from urate crystalluria.37 Other investigators14 have reported that the cytoplasm of apical bladder epithelial cells is expanded with mucin granules in free-ranging desert tortoises with urolithiasis. For the tortoise of the present study, the bladder wall mucinosis might have been induced by the presence of suture in the bladder wall from the cystotomy or inflammation associated with surgery and chronic urolithiasis. For the tortoise of the present study that had a nonhealing plastronotomy flap, it was theorized that failure to place a barrier (typically bone wax) between the surgical bone incision in conjunction with the irregular edge of the plastronotomy incision allowed the epoxy used in the plastron patch to leak into the surgical bone incisions and inhibit healing.36 Clinicians considering surgical removal of uroliths from chelonians should be aware of potential postoperative complications. In the present study, 2 of 12 chelonians died following cystotomy via plastronotomy, 1 of 3 died following lithotripsy, and 1 of 2 died following digital removal of a cloacolith. Complication and mortality rates for these 3 procedures may differ for many reasons, including patient health status, anesthesia protocol used, and surgeon experience and comfort. To our knowledge, complication and mortality rates are not currently available for other surgical procedures for urolith removal in chelonians such as bladder marsupialization via a prefemoral incision.12,a
Necropsy was performed on 18 of the chelonians of the present study, and urolithiasis contributed to the decision to euthanize or was the cause of death for 9. In those 9 chelonians, abnormalities identified during necropsy were primarily associated with the urinary tract. Those findings suggested that early diagnosis and treatment of urolithiasis is necessary to prevent morbidity and death, and chelonian owners should be informed of potential life-threatening outcomes such as tear or rupture of the bladder wall that may occur if urolithiasis is not treated.
Results of the present study indicated that client-owned chelonians with urolithiasis can have a variety of clinical signs and physical examination abnormalities that may or may not be directly referable to the urinary tract. Hematologic, biochemical, and urinalysis findings for the chelonians of this study were nonspecific for diagnosis of urolithiasis. Many of the chelonians in this study died or were euthanized as a consequence of urolithiasis, which suggested that early identification and appropriate intervention should be pursued to correct this disease. Postoperative complications associated with cystotomy via plastronotomy were infrequent and included bladder wall mucinosis and failure of plastronotomy patch healing. The acquisition of comprehensive dietary and environmental history for client-owned chelonians with urolithiasis is necessary to elucidate the etiology of the disease.
ABBREVIATIONS
| AST | Aspartate aminotransferase |
| CK | Creatine kinase |
Lamberski N, San Diego Zoo Safari Park, Escondido, Calif: Personal communication, 2014.
Universal polarizing microscope, Carl Zeiss Inc, Thornwood, NY.
Impact 410 spectrometer, Nocolet Instrument Corp, Madison, Wis.
OMNIC Software Suite, Nocolet Instrument Corp, Madison, Wis.
Therm Electron Corp, Asheville, NC.
ISIS Physiological Data Reference Values Project, Apple Valley, Minn: International Species Information System (ISIS), 2010.
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