A 6-month-old 20.6-kg (45.3-lb) sexually intact male Clumber Spaniel was presented for routine castration. The dog's rectal temperature (37.9°C [100.2°F]), heart rate (100 beats/min), and respiratory rate (16 breaths/min) were within reference intervals, and the dog had a small but proportional stature, a reducible umbilical hernia, and mild otitis externa. History of an adverse reaction (restlessness, weakness, and crawling ambulation of 2 days’ duration) to vaccination against leptospirosisa was reported. Spinosad and milbemycin oximeb were given monthly for the prevention of flea infestations and endoparasitism.
At 6 months of age, pertinent findings of CBC and serum biochemical analyses included a non-anemic RBC count (5.8 × 106 cells/μL; reference interval, 5.4 × 106 to 8.7 × 106 cells /μL), low Hct (31%; reference interval, 38% to 56%), microcytosis (mean corpuscular volume, 55 fL; reference interval, 59 to 76 fL), hypochromasia indicated by low mean corpuscular hemoglobin (19.5 pg; reference interval, 21.9 to 26.1 pg) yet normal mean corpuscular hemoglobin concentration (35.5 g/dL; reference interval, 32.6 to 39.2 g/dL), reticulocyte count (23 × 103 cells/μL; reference interval, 10 × 103 to 110 × 103 cells/μL), hypoproteinemia (5.0 g/dL; reference interval, 5.5 to 7.5 g/dL), hypoalbuminemia (2.2 g/dL; reference interval, 2.7 to 3.9 g/dL), hypocholesterolemia (108 mg/dL; reference interval, 131 to 345 mg/dL), high activities of alanine aminotransferase (192 U/L; reference interval, 18 to 121 U/L) and alkaline phosphatase (498 U/L; reference interval, 5 to 160 U/L), and total bilirubin concentration within the reference interval (0.2 mg/dL; reference interval, 0.0 to 0.3 mg/dL). Preprandial serum total bile acids concentration was within reference intervals, but random and 2-hour postprandial serum total bile acids concentrations were high (35 and 43 μmol/L, respectively; reference interval, < 25 μmol/L). Results of coagulation tests (prothrombin time, activated partial thromboplastin time, and protein C activity) were within reference intervals. Because of historic intermittent episodes of diarrhea, serum biomarkers of gastrointestinal and pancreatic diseases were also evaluated; serum concentrations of cobalamin (447 ng/L; reference interval, 284 to 836 ng/L), folate (7.7 μg/L; reference interval, 4.8 to 19.0 μg/L), and canine-specific pancreatic lipase (42 μg/dL; reference interval, 0 to 200 μg/dL) were within reference intervals. An ACTH stimulation test was performed to exclude hypoadrenocorticism from consideration as a diagnosis; results were unremarkable.
On the basis of the dog's small stature and the discovery of microcytosis, hypocholesterolemia, hypoalbuminemia, and high total serum bile acids concentration, castration was postponed and abdominal ultrasonography was pursued. Ultrasonography revealed a liver of normal size, contour, and echotexture and a modestly distended gallbladder with thin walls, anechoic fluid (bile), and small echogenic particulates with acoustic shadows (consistent with nonobstructive cholelithiasis). Immediately after completion of ultrasonography, the dog was anesthetized and 2 ultrasound-guided 16-gauge needle biopsy specimens were collected from the liver. Biopsy samples were placed in neutral-buffered 10% formalin and submitted to a veterinary diagnostic laboratory for processing and diagnostic interpretation. Mild hemorrhage from the liver was noted ultrasonographically after the biopsy, but self-resolved.
The histologic report indicated chronic locally extensive portal hepatitis with severe lymphoplasmacytic infiltrates, biliary hyperplasia, bridging portal fibrosis, hepatic lobular atrophy, mild arteriolar hyperplasia, and hemosiderin-laden macrophages. The veterinary pathologist interpreted these findings as nonspecific and reactive, likely reflecting disease involving the gastrointestinal tract, pancreas, or biliary system.
Seeking a second opinion, the attending veterinarian submitted 5 unstained slides of sections of paraffin-embedded liver to the Animal Health Diagnostic Center at Cornell University.
Slides were stained with H&E, reticulin, Masson trichrome, Prussian blue, and rhodanine stains. Light microscopic examination revealed that the hepatocytes were small and had a greater than normal frequency of binucleation. Portal tracts and central veins were in abnormally close apposition, consistent with remodeling or atrophy. Serpiginous arterial profiles accompanied proliferative bile ductules and cholangiocytes (ductular reaction) with small numbers of lymphocytes and fewer plasma cells aligning along bridging fibrotic partitions (portal-to-portal and portal-to-central bridging). Prominent aggregates of macrophages engorged with nongranular dark red to brown phagocytized material marginated the fibrotic partitions. Minute foci of this pigmented material were also observed within the cytoplasm of some hepatocytes and occasionally bulged canalicular profiles. No necrotic hepatocytes were identified. Pigmented material did not stain with Prussian blue stain, thereby excluding iron from consideration. The possibility that the pigmented material was copper could not be determined from the examination of rhodanine-stained slides because of the tinctorial overlap between the orange to red color of stainable copper and orange-inked margins of the initial biopsy specimens; personnel at the first diagnostic laboratory had applied orange ink to demarcate tissue margins. Additional slides could not be prepared because the block of paraffin-embedded liver tissue had been depleted. Another liver biopsy at the time of castration was advised to further characterize the aforementioned histologic changes, including the unusual pigmented material. Meanwhile, the dog was fed a prescription diet purported to support liver healthc and administered UDCA (20 mg/kg [9.1 mg/lb], PO, q 24 h, with food) and a SAMe-silybin supplementd (20 mg/kg, PO, q 24 h, without food); spinosad and milbemycin oxime continued to be administered monthly.
At 2 years of age, the dog was returned for castration. Vital signs were again within reference intervals, body weight was 24.8 kg (54.6 lb), the dog was still of small but proportional stature, and erythematous, crusting, alopecic lesions affected the dorsal aspect of its head and back. No jaundice was evident. Results of CBC indicated an unremarkable Hct (45%) and RBC count (8.0 × 106 cells/μL), persistent microcytosis (mean corpuscular volume, 56 fL) and hypochromasia indicated by low mean corpuscular hemoglobin (20.8 pg), and unremarkable mean corpuscular hemoglobin concentration (37.2 g/dL) and reticulocyte count (36 × 103/μL). Results of serum biochemical analyses indicated a mild but improved hypoalbuminemia (2.6 g/dL), mild hyperbilirubinemia (0.6 mg/dL), and high activities of alanine aminotransferase (281 U/L), alkaline phosphatase (247 U/L), and aspartate aminotransferase (281 U/L; reference interval, 16 to 55 U/L). A 2-hour postprandial serum total bile acids concentration was higher (107 μmol/L) than before. Urinalysis results indicated a specific gravity of 1.036, pH of 8.5, and 2+ bilirubinuria; besides bilirubinuria, no additional abnormalities were noted by means of urine dipstick analysis, and microscopic sediment analysis was unremarkable.
The dog was premedicated with butorphanol (0.2 mg/kg [0.09 mg/lb], IM), and anesthesia was induced with propofol, IV, to effect and maintained with isoflurane in oxygen. A routine closed castration was performed without complication. After castration, a laparotomy was performed and the liver was examined. Grossly, the liver had an unusual black color, was markedly reduced in size with sharp margins, and had an irregular surface with uniformly distributed tan pinpoint spots. A wedge biopsy specimen of the liver was obtained, and the tissue was placed in neutral-buffered 10% formalin and submitted to the Animal Health Diagnostic Center. The dog recovered from the procedures and anesthesia without complications.
Histologic examination of liver sections included the same stains originally used, and sections did not have inked margins. Additionally, Hall and periodic acid–Schiff stains (with and without diastase) were used to investigate for canalicular bile casts and glycoprotein, respectively, associated with the unusual dark red to brown pigmented material noted previously. With H&E stain, numerous small regenerative nodules marginated by dissecting portal-to-portal and portal-to-central fibrotic septa were seen (Figure 1). Fibrotic septa were associated with abundant proliferative bile duct profiles and aggregates of macrophages engorged with dark red to brown pigment. Similar pigment variably engorged the bile canaliculi, including some canaliculi that were massively distended, resulting in a bulbous, sausage-like segmented silhouette. Pigment also appeared as tiny globules within the cytoplasm of hepatocytes and biliary epithelial cells but was not evident within the lumens of bile ducts. Portal regions and fibrotic septa were infiltrated by variably sized aggregates of plasma cells, fewer lymphocytes, and rare neutrophils. The inflammatory infiltrates approximated aggregates of pigment-engorged macrophages. Up to 7 necrotic hepatocytes/10 hpf were seen, compared with ≤ 1 necrotic hepatocyte/10 hpf for a healthy canine liver. With reticulin stain, widespread regenerative nodules with portal-to-portal and portal-to-central bridging fibrotic septa as well as centrilobular parenchymal collapse were noted. Deposition of fibrillar collagen within dissecting fibrotic septa but not along hepatic sinusoids was seen with Masson trichrome stain. The pigment failed to stain with Prussian blue, rhodanine, Hall, and periodic acid–Schiff stains, indicating that the pigment was not iron, copper, bile casts, or glycoprotein, respectively. With polarized microscopy, the pigment had yellow to green birefringence with occasional Maltese cross configurations (Figure 2). Histologic findings were consistent with severe PH. Progressive liver injury and canalicular distension were compatible with the emerging hyperbilirubinemia.
Photomicrographs at increasing magnification of sections of a wedge liver biopsy specimen from a 2-year-old Clumber Spaniel with congenital EPP and PH. A—Early regenerative nodules and unusual dark red to brown pigment distributed along bridging fibrotic septa emerging from portal regions. H&E stain; bar = 3 mm. B—Large aggregate of pigment-engorged macrophages within bridging fibrotic septa emerging from a portal region. H&E stain; bar = 200 μm. C—Pigment-engorged bile canaliculi (arrows) and scattered pigment-laden macrophages (asterisks). H&E stain; bar = 60 μm.
Citation: Journal of the American Veterinary Medical Association 257, 11; 10.2460/javma.2020.257.11.1148
Photomicrograph of a section of a wedge liver biopsy specimen collected from the dog of Figure 1. Polarized microscopy reveals aggregates of birefringent pigment within engorged macrophages and pigment occasionally arranged in a Maltese cross configuration (arrows). H&E stain; bar = 400 μm (90 μm in inset).
Citation: Journal of the American Veterinary Medical Association 257, 11; 10.2460/javma.2020.257.11.1148
Samples of blood, urine, and feces were collected from the patient and 2 healthy control dogs for porphyrin analyses. Additionally, total porphyrin and protoporphyrin concentrations were measured in liver tissues preserved in neutral-buffered 10% formalin that had been collected from the patient and 2 anicteric dogs. The 2 anicteric dogs did not have necroinflammatory liver disease and had been euthanized because of congenital hepatic vascular malformation or splenic hemangiosarcoma. All samples were protected from light and stored at −80°C and shipped frozen. Plasma, RBC, urine, fecal, and liver tissue concentrations of porphyrin and porphyrinogen were determined at the Porphyria Laboratory at the University of Texas Medical Branch. Analyses indicated a > 100-fold increase in RBC protoporphyrin concentration in the patient, compared with results for the control dogs, with a predominance of metal-free protoporphyrin (Table 1; Supplementary Table S1, available at: avmajournals.avma.org/doi/suppl/10.2460/javma.257.11.1148). Urine concentrations of the porphyrin precursors ALA and PBG were not increased. Relative to results for the control dogs, the patient's total porphyrin concentrations were increased in plasma (approx 4.5-fold), urine (approx 3-fold), feces (approx 32-fold), and liver tissue (approx 1,538-fold). Compared with the anicteric dogs (1.9 and 2.3 nmol/g of dry weight liver), the patient had a substantially greater (approx 1,354-fold) liver total protoporphyrin concentration (2,844 nmol/g of dry weight liver). Small amounts of di- (approx 288 nmol/g of dry weight) and tricarboxylated (approx 175 nmol/g of dry weight) porphyrins were also detected in the patient's liver tissue but not detected in the liver tissue of the other dogs. The liver tissue of one of these other dogs, however, contained a trivial amount of pentacarboxyl porphyrin.
Plasma, RBC, urine, fecal, and liver porphyrin concentrations and urine porphobilinogen concentration in samples collected from a 2-year-old Clumber Spaniel with congenital EPP and complicating PH and from 2 healthy control dogs (plasma, RBCs, urine, and feces) and 2 anicteric dogs without necroinflammatory liver disease (liver).
| Sample | Analyte | Clumber Spaniel | Control dog 1 | Control dog 2 | Reference interval* |
|---|---|---|---|---|---|
| Plasma | Total porphyrins (μg/dL) | 4.5 | 1.0 | 0.9 | ≤ 1.0 |
| RBCs | Total porphyrins (μg/dL) | 5,496 | 51 | 51 | 15–60 |
| Protoporphyrin (% of total) | 86.3 | — | — | > 80 | |
| Metal-free protoporphyrin (%) | 92 | — | — | < 50 | |
| Zinc protoporphyrin (%) | 8 | — | — | > 50 | |
| Urine | ALA (mg/g of creatinine) | 1.0 | 0.8 | 1.3 | 0–7 |
| PBG (mg/g of creatinine) | 1.0 | 1.6 | 2.1 | 0–4 | |
| Total porphyrins (nmol/g of creatinine) | 444 | 141 | 141 | 15–60 | |
| Feces | Total porphyrins (nmol/g of dry weight) | 1,479 | 50 | 42 | 15–60 |
| Protoporphyrin (% of total) | 18.1 | 8.7 | 12.1 | > 80 | |
| Liver | Total porphyrins (nmol/g of dry weight) | 3,307 | 1.9 | 2.4 | < 2 |
| Protoporphyrin (% of total) | 86 | 100 | 97.9 | — |
Reference intervals pertain to respective samples from people without porphyric syndromes.
— = Not available.
See Supplemental Table S1 for complete results.
Fluorescence scanning of the patient's diluted plasma (to achieve a neutral pH) yielded a fluorescence emission peak at a wavelength of 627 nm that was not evident for the control dogs’ plasma. Collective clinicopathologic and histologic examination findings, results of comprehensive porphyrin profiling and plasma fluorescence scanning, and the young age of the Clumber Spaniel of the present report were consistent with a diagnosis of congenital EPP complicated by severe progressive PH.1–10
Management of this dog's condition included administration of SAMe-silybin and UDCA as previously prescribed and an antimicrobial as needed for presumed solar dermatitis complicated by bacterial pyoderma, feeding of the previously mentioned prescription diet,c and minimization of sunlight exposure; routine prophylactic medication to control ecto- and endoparasitism was maintained. At 4 years of age, the dog was clinically stable with the exceptions of fluctuating serum alanine aminotransferase and alkaline phosphatase activities and suspected EPP-related solar dermatopathy.
Discussion
Porphyria syndromes reflect disrupted heme synthesis, and clinical signs are associated with the accumulation of intermediates of the heme synthetic pathway: porphyrins (heme, protoporphyrin, and oxidative products of porphyrinogens) and porphyrin precursors (ALA and PBG; Figure 3; Supplementary Table S2, available at: avmajournals.avma.org/doi/suppl/10.2460/javma.257.11.1148).11–13 Heme synthesis is orchestrated by 8 sequential cytosolic and mitochondrial enzymes predominantly located in the bone marrow and liver.11–15 Enzyme defects cause signature accumulations of upstream or, in some instances, upstream and downstream pathway intermediates in the blood, urine, and feces. Comprehensive porphyrin profiling is used to deduce the pathway site of disrupted heme synthesis and informs the classification of associated clinical syndromes in people.12–14,16 However, interpretation of porphyrin profiles can be complicated by cyclic illnesses as well as renal and hepatic dysfunction that impacts analyte production and elimination.17,18 Genetic testing of people with suspected congenital porphyric syndromes is the diagnostic standard because of the numerous defined mutations.11
Diagram of the heme synthesis pathway. Porphyria syndromes develop when heme synthesis is disrupted and intermediates accumulate within tissues. The dog of Figure 1 had congenital EPP, with a defect in FECH, the terminal enzyme in the pathway.
Citation: Journal of the American Veterinary Medical Association 257, 11; 10.2460/javma.2020.257.11.1148
Grossly, marked hepatic protoporphyrin accumulation, as shown for the dog of the present report (approx 1,354-fold increase), imbues the liver with a dark brown to black color. Histologic findings for the liver specimens collected from the dog at 6 months and 2 years of age confirmed a progressive hepatopathy. Protoporphyric hepatopathy initiates in periportal regions with progressive development of fibrotic bridging septa that are marginated by porphyrin-engorged macrophages, mixed inflammatory infiltrates, and single necrotic hepatocytes and cholangiocytes.2,4,9,14 A distinctive feature of PH, as reported19 for dogs with acquired PH and also noted for the dog of the present report, is a striking yellow to green birefringence, indicative of accumulated pigment, and unique Maltese cross pigment aggregates in H&E-stained liver tissue examined with polarized microscopy. Ultrastructural studies2,3,9 of PH in rodents and people have shown needle-like crystalline protoporphyrin precipitates plugging bile canaliculi and accumulating in hepatic macrophages. Similar crystals, lightly scattered in the cytoplasm of hepatocytes and cholangiocytes, corresponded with pigment distribution observed with light microscopic examination of this dog's liver tissue.
Because heme can be synthesized in all tissues and serves as the prosthetic group for hemoglobin, myoglobin, cytochrome P450 enzymes, enzymes of mitochondrial oxidative phosphorylation, and the antioxidant enzymes catalase and glutathione peroxidase, diverse clinical signs of porphyric syndromes manifest in people.16,20 Porphyrins and porphyrin precursors initially accumulate in the cells and tissues (eg, bone marrow, RBCs, and liver) where the dysfunctional enzyme is ordinarily most active. Ultimately, they disseminate systemically and are eliminated in urine and bile (feces), depending on their solubility in water. Identification of porphyrins in plasma, RBCs, serum, urine, feces, bile, or hepatocytes suggests a pathologic condition because porphyrins and their intermediates do not normally accumulate. For the dog of the present report, plasma protoporphyrin emitted a peak fluorescence of 627 nm, consistent with EPP. This wavelength is slightly different from that in affected people (634 nm),12,13 possibly owing to a difference in protoporphyrin's avidity for protein binding.e Photoactivation of some porphyrin intermediates can cause a photoreactive dermatopathy and hemolysis. Because photoactivating light passes through window glass and is also emitted from certain types of incandescent light, photoreactive dermatopathy may develop when indoors, unless lights are equipped with yellow filters.12–14,20 A severe consequence of hepatic porphyrin accumulation is the development of PH and, in people, subsequent development of chronic hepatitis, fibrosis, cirrhosis, liver failure, and an increased risk for hepatic malignancies.4–6,13,14,16,20,21
Congenital and acquired porphyric syndromes have been characterized in numerous species, including people,12,13,16,17 cattle,22–27 pigs,28,29 sheep,30 rodents,31 cats,32–37 fox squirrels,38 African hedgehogs,39 and dogs.19,40,41 Congenital syndromes affecting people are classified into 8 clinical disorders, with EPP as the third most common. Congenital EPP has been linked with > 100 mutations, with the predominant defect involving mitochondrial FECH, the terminal enzyme of heme biosynthesis.13 Because FECH catalyzes the insertion of ferrous iron into the open ring of protoporphyrin IX, deficient FECH leads to hypochromic microcytosis and, occasionally, anemia.11,13,15,16,20 Because FECH also catalyzes the insertion of zinc into protoporphyrin, EPP is also characterized by the accumulation of metal-free protoporphyrin, as noted for the dog of the present report. Conversely, increased plasma concentrations of protoporphyrin with zinc are associated with lead poisoning, iron deficiency, and anemia of chronic disease, reflective of normal FECH activity.12,13,16 Although all nucleated cells have mitochondrial FECH (heme needed for the cytochromes of the mitochondrial respiratory chain), most FECH activity orchestrates hemoglobin synthesis in the bone marrow. Thus, insufficient FECH activity in individuals with congenital EPP initially causes protoporphyrin accumulation in the reticulocytes, with later dispersal to the skin and other tissues, including the liver for biliary elimination.15,16,22 We propose that, similar to people with congenital EPP, protoporphyrin derived from the bone marrow and liver contributed to the hepatic protoporphyrin accumulation for the dog of this report. Partial rather than complete loss of heme synthetic capacity is implicated in this dog because of the persistent hypochromic microcytosis without anemia at 2 years of age, signifying some FECH activity.
Congenital EPP initially manifests at a young age in people as a painful, nonblistering photoreactive dermatopathy,13 similar to the chronic dermatopathy recognized in the dog of the present report. Whereas 30% of people with EPP develop liver injury, only 5% progress to critical PH.8,10,11,13,15,20 Liver injury is typically associated with fluctuating liver enzyme activity and occasional hyperbilirubinemia.
Although most porphyric syndromes are congenital, acquired forms may develop after exposure to certain xenobiotics, causing hepatic but not bone marrow suppression of FECH.17,42–44 In dogs, acquired PH has been induced by administration of an undisclosed antipsychotic agent19 and a drug with a molecular configuration and action similar to levetiracetam41 and by probable exposure to an unidentified environmental toxin.40 For the dogs of the aforementioned reports,19,40,41 PH was confirmed histologically but detailed porphyrin analyses were not performed and microcytosis and dermatologic lesions were not described.
Pathologic accumulation of porphyrins reflects their relative water solubility, largely influenced by the number of carboxylic acid groups per molecule.11,12,42 Uroporphyrin (8 carboxyl groups) is eliminated in urine, and coproporphyrin (4 carboxyl groups), coproporphyrinogen, uroporphyrinogen, and complex carboxylated forms (penta-, hexa-, and heptacarboxyl porphyrinogens) are eliminated in urine and bile (feces).14 Protoporphyrin (2 carboxyl groups) is hydrophobic with exclusive biliary elimination (without conjugation) and undergoes some enterohepatic circulation.4,13,14,16,17,20 Because canalicular clearance is the rate limiter for protoporphyrin elimination, canalicular aggregation of protoporphyrin crystals causes cholangiocyte injury and cholestasis, thereby unleashing a vicious cycle that worsens liver injury.13,14,16,20 With EPP, substantial liver injury can lead to the accumulation of upstream porphyrin and porphyrinogen products including complex carboxylated forms, as demonstrated in the dog of the present report. This has been attributed to progressive decline in hepatic uroporphyrinogen decarboxylase activity.13–15,18,45 Hepatic dysfunction also decreases fecal protoporphyrin and increases urinary coproporphyrinogen I concentrations.6,15,45 Indeed, a 5- to 6-fold increase in urinary coproporphyrins, a > 1,000-fold increase in fecal di- and tricarboxyl porphyrins, and low fecal protoporphyrin concentrations were documented in this dog, reflecting the impact of PH.
As the single route of protoporphyrin elimination, the liver is prone to protoporphyrin-associated injury. In people, the risk for PH correlates with the severity of hepatic and circulating protoporphyrin concentrations (eg, RBC protoporphyrin concentration > 2,000 μg/dL).5,14 The dog of the present report had a markedly increased RBC protoporphyrin concentration (4,743 μg/dL), compared with results for the control dogs (< 52 μg/dL), such that development of PH was expected.
People with PH present for acute and rapidly progressive illness associated with increasing liver enzyme activity and hyperbilirubinemia.10–13 No PH-related clinical illness was evident in the dog of the present report through 4 years of age. Although ultrasonographic examination initially revealed probable gallbladder choleliths, no postprandial clinical signs or hyperbilirubinemia consistent with cholelith-related complications were documented through 4 years of age. Identification of choleliths was not surprising because they develop in 30% of people with EPP, likely because of accumulation of insoluble protoporphyrin crystals in bile.6,10,11,13,20
In the dog of the present report, the transient painful paretic episode (crawling posture) after administration of a Leptospira vaccine may have represented an EPP-related neuropathic crisis. In people, transient and progressive sensory and motor neuropathic events are associated with extreme protoporphyrinemia, with protoporphyrin concentrations as high as that in the dog of the present report.13,46–49 Vaccination may have instigated an acute inflammatory response and subsequently this event, associated with the induction of heme oxygenase and surging circulating protoporphyrin concentrations.50,51
Goals for the management of patients with EPP include avoidance of conditions that can induce heme synthesis and activity of cytochrome P450 enzymes, stabilization of hepatic heme concentration, reduction of plasma protoporphyrin concentration, promotion of choleresis that may facilitate biliary protoporphyrin excretion, supplementation with antioxidants and hepatoprotectants that may slow the progression of protoporphyric liver injury, reduction of enteric absorption of protoporphyrin undergoing enterohepatic circulation, and prompt treatment of concurrent illnesses, including infections.14 Induction of cytochrome P450 enzymes accelerates hepatic heme synthesis and subsequently increases the risk of protoporphyrin accumulation12,14,42; therefore, medications known to induce these enzymes should be avoided. Many drugs and illnesses may acutely worsen porphyric syndromes.12,14 Although discussion of these drugs and illnesses is beyond the scope of this report, they should be thoughtfully considered when managing a porphyric patient.4,11,14,42
Ursodeoxycholic acid, SAMe-silybin, and vitamin E were administered to the dog of this report. Although no consensus exists among physicians regarding the benefit of UDCA for people with PH,5,13,52–54 it may facilitate biliary excretion of protoporphyrin and have membranoprotective and anti-inflammatory effects. Vitamin E and SAMe were prescribed because of their antioxidant and membranoprotective properties and because of SAMe's choleretic effect (glutathione non–bile acid–dependent bile flow).13,55,56 Additional salvage interventions that may remove protoporphyrins undergoing enterohepatic circulation include administration of cholestyramine and activated charcoal.13,57–59 However, as with UDCA, no consensus exists among physicians regarding the effectiveness of these interventions. Caution is warranted with long-term administration of cholestyramine (a bile acid sequestrant) and, potentially, activated charcoal. Through nonspecific binding, these agents may limit intestinal absorption of micronutrients, vitamins, and coadministered medications. Specifically, cholestyramine interferes with the absorption of fat-soluble vitamins and bile acids (eg, UDCA).60 Cholestyramine and activated charcoal were not yet considered for the dog of the present report because clinical signs were not overtly progressive and the owner was reluctant to pursue additional treatments.
Proper nutrition is also crucial for managing protoporphyrin syndromes.55,61 For people with acute porphyric illness, fasting is avoided because it is thought to induce hepatic heme synthesis and, therefore, increase protoporphyrin production.61 Although controversial, glucose supplementation (PO or IV) has been advocated for people with acute porphyric illnesses to suppress heme oxygenase through suppression of ALA synthase 1 activity.61–63 The dog of the present report was fed a diet purported to support liver health but also a variety of hypoallergenic prescription diets because of concern that atopic dermatitis may have contributed to the skin lesions.
Acute decompensation of PH in people can be transiently mitigated by IV administration of hemin (protoporphyrin IX containing ferric iron), which curtails heme synthesis through negative feedback and, therefore, protoporphyrin production.13,20,64 Additionally, acute decompensation may be mitigated with a blood transfusion for anemic patients; transfused blood suppresses heme synthesis associated with hematopoietic activity.13,20,64 Other mitigation strategies include RBC exchange transfusion, which may reduce RBC protoporphyrin concentrations, and plasmapheresis, which may remove circulating protoporphyrin.7,13,14 Although canine-specific hemin is not available, blood transfusion, RBC exchange transfusion, and plasmapheresis are available as salvage options for dogs. The ultimate treatment for people with PH is liver transplantation and subsequent bone marrow transplantation to restore the FECH activity.13,20,64
In summary, features that supported a diagnosis of congenital EPP in the dog of the present report included its young age; markedly high protoporphyrin concentrations in the plasma, RBCs, feces, and liver; predominance of metal-free protoporphyrin; absence of high urine ALA and PBG concentrations (excluding lead poisoning as a cause); unique porphyrin fluorescence peak on UV light activation; and classic progressive PH.13–17 This report illustrated that the histologic diagnosis of PH is challenging and can be overlooked. Protoporphyric hepatopathy should be considered when histologic examination with light microscopy of a young dog's liver tissue shows engorged macrophages with nongranular dark red to brown pigmented material; stains to detect iron, copper, bile, and glycoprotein fail to stain the pigment; and examination with polarized microscopy shows that the pigment has a yellow to green birefringence.
Acknowledgments
No third-party funding or support was received for this study or the writing or publication of the manuscript. The authors declare that there were no conflicts of interest.
Presented as a poster at the International Congress on Porphyrins and Porphyrias, Milan, Italy, September 2019.
ABBREVIATIONS
| ALA | δ-Aminolevulinic acid |
| EPP | Erythropoietic protoporphyria |
| FECH | Ferrochelatase |
| PBG | Porphobilinogen |
| PH | Protoporphyric hepatopathy |
| SAMe | S-adenosylmethionine |
| UDCA | Ursodeoxycholic acid |
Footnotes
LeptoVax4, Elanco, Greenfield, Ind.
Trifexis, Elanco, Greenfield, Ind.
LD Prescription Diet, Hill's Pet Nutrition Inc, Topeka, Kan.
Denamarin, Nutramax, Edgewood, Md.
Anderson KE, Porphyria Laboratory, University of Texas Medical Branch, Galveston, Tex: Personal communication, 2019.
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