History
A 14-year-old male Western chuckwalla (Sauromalus ater) was evaluated because of a left-sided head tilt of several days’ duration. In addition to the head tilt, abnormalities present on physical examination included weight loss. The left eye was closed most of the time with a circular, irregular plaque adhered to the dorsal aspect of the cornea; the left humerus was enlarged and irregular; and coelomic palpation revealed a firm, gritty mass in the right caudal quadrant.
Abnormalities detected on a CBC included anemia (PCV, 21%; reference range,1 31.6% to 44%) and basophilia (1,170 basophils/μL; reference range, 42 to 192 basophils/μL). Serum biochemical abnormalities included hypocalcemia (6.0 mg/dL; reference range, 9.7 to 17.7 mg/dL), hyperphosphatemia (12.4 mg/dL; reference range, 2.5 to 8.9 mg/dL), hypoalbuminemia (1.7 g/dL; reference range, 2.9 to 3.7 g/dL), high aspartate aminotransferase activity (80 U/L; reference range, 7 to 19 U/L), and high creatine kinase activity (2,767 U/L; reference range, 0 to 2,465 U/L). Whole body radiographs were obtained (Figure 1).
Horizontal right lateral (A) and dorsoventral (B) radiographic views of the whole body of a 14-year-old Western chuckwalla (Sauromalus ater) evaluated because of head tilt, cachexia, and an abnormal humerus.
Citation: Journal of the American Veterinary Medical Association 242, 9; 10.2460/javma.242.9.1215
Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page →
Radiographic Findings and Interpretation
On the dorsoventral view, there is a starburst-shaped mineral opacity in the caudal right portion of the coelom and a tubular mineral opacity in the caudolateral right portion of the coelom composed of many pinpoint mineralized opacities. The left humerus is shortened and thickened, compared with the right. There is a triangular mineral opacity cranial and slightly distal to the left elbow joint, and the proximal portion of the left radius is displaced caudally. On both views, there are sclerotic, enlarged regions of many ribs and multiple tortuous, tubular, mineralized structures in the lung fields and cranial portion of the coelom that run ventral and parallel to the vertebrae (Figure 2). The radiographic interpretation was a cystic calculus, mineral ingesta (likely sand) in the colon, a healed malunion fracture of the distal aspect of the left humerus with a displaced bone fragment, subluxation of the proximal portion of the left elbow joint, multiple healed rib fractures, and diffuse vascular mineralization, including the aorta. Differential diagnoses included secondary renal hyperparathyroidism, secondary nutritional hyperparathyroidism, and neoplasia.
Same radiographic views as in Figure 1. On the dorsoventral (B) view, there is a round mineral opacity with a starburst formation (black arrowheads), a healed malunion fracture of the distal portion of the left humerus with a fragment, and subluxation of the proximal portion of the radius (small arrow). On both views (A and B), there are multiple mineralized tubular structures in the lung fields and cranial part of the coelom and parallel to the vertebrae (large arrows) as well as numerous healed rib fractures (white arrowheads). The mineralization of the aorta is best appreciated on the lateral view.
Citation: Journal of the American Veterinary Medical Association 242, 9; 10.2460/javma.242.9.1215
Treatment and Outcome
The lizard was given 8 mL of electrolyte solution SC on the day of physical examination followed by 6 mL every 48 hours. The lizard's condition continued to decline, and it became listless and lethargic. On day 12, the lizard was moribund, had tremors in the hind limbs, and was bradycardic. The lizard was anesthetized with isoflurane and euthanized via intracardiac administration of sodium pentobarbital and phenytoin.
On gross necropsy, the lizard was emaciated and had free coelomic fluid. Both kidneys were pale and swollen. The urinary bladder had a large, irregular urolith, which was composed of 100% salts of uric acid. The aorta was completely mineralized.
Histologic examination revealed chronic nephritis with marked distention and renal tubular mineralization. Renal tubules were diffusely dilated and contained mineralized material or urates, and the interstitium had diffuse severe fibrosis and moderate edema. Mineralized material deposits were found throughout the tunica media of the aorta and great vessels. The gastric mucosa had multifocal subacute necrosis and mineralization, which also occurred within the lungs and the spleen. The final diagnosis was cystic calculus, severe interstitial nephritis, and marked renal fibrosis. Multiorgan mineralization was noted secondary to uremia and the calcium-phosphorous imbalance.
Comments
Abdominal palpation and whole body radiography during routine examination of reptiles are crucial to diagnose cystic calculi. Radiographically, urate stones often appear as soft tissue opacities in species other than reptiles. In reptiles, however, cystic calculi are usually composed of potassium or calcium urate salts, which appear as mineral opacities on radiographs. Cystic calculi occur more often in male than female reptiles and are usually located in the left lobe of the reptilian bladder.2 The causes of stone formation include hypovitaminosis A, hypovitaminosis D, calcium deficiency, excess dietary potassium, excess dietary protein, decreased bladder emptying, bacterial infection, and suture remnants.2,3 Lethargy, signs of depression, anorexia, constipation, hind limb paresis, and dystocia have been reported as clinical signs, but cystic calculi can also be subclinical.2
Cystic calculi can be removed by cystotomy, and small stones can be retrieved endoscopically or with long forceps.2 Because reptilian bladders are not sterile, antimicrobial treatment is recommended prior to surgery.2
In renal failure, serum uric acid concentration increases substantially only when profound renal damage has occurred.4 The serum calcium-to-phosphorus concentration ratio is a good indicator of renal function in reptiles.4 The calcium-to-phosphorus concentration ratio should be > 1; a ratio < 1 is consistent with renal disease. The chuckwalla of this case report had a calcium-to-phosphorus concentration ratio of 0.484. Another indicator of renal function is the solubility index, which is calculated by multiplying the serum calcium concentration (mg/dL) by the serum phosphorous concentration (mg/dL). The solubility index should be < 55.4 The chuckwalla of the present report had a solubility index of 74.4. Although both indicators of renal function can guide clinicians, a renal biopsy is required to make a definitive diagnosis.
Secondary hyperparathyroidism, whether renal or nutritional in origin, will cause a reduction of calcium in bones, leading to fractures. The malunion humeral fracture and the multiple rib fractures in this chuckwalla support the diagnosis of chronic secondary hyperparathyroidism. Considering that overall skeletal opacification was good and the lizard was mature and had no previous history of metabolic bone disease, the hyperparathyroidism was likely secondary to renal disease.
1. International Species Information System. ISIS physiological reference values for San Esteban Island chuckwalla (Sauromalus varius). Apple Valley, Minn: International Species Information System, 2002.
2. Mader DR. Calculi: urinary. In: Reptile medicine and surgery. 2nd ed. St Louis: Saunders Elsevier Inc, 2006; 763–771.
3. Girling SJ, Raiti P. Urogenital system. In: BSAVA manual of reptiles. 2nd ed. Gloucester, England: British Small Animal Veterinary Association, 2004; 261–272.
4. Fudge AM. Reptilian renal and reproductive disease diagnosis. In: Laboratory medicine avian and exotic pets. Philadelphia: WB Saunders Co, 2000; 217–222.