Fanconi syndrome with hepatorenal karyomegaly in a young Sphynx cat

CASE SUMMARY: A 3-year-old male neutered Sphynx cat was referred for history of chronically increased liver enzymes and lower urinary tract signs that were first reported when the cat was 5 months old. Urine metabolic profile revealed increased amino aciduria and glucosuria despite normoglycemia, suggesting Fanconi syndrome. Urine sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a banding pattern suggestive of primary tubular damage. Serial blood work showed non-regenerative normocytic normochromic anemia, persistently elevated liver enzymes, worsening azotemia and progressive hyperchloremic metabolic acidosis. Ultrasound revealed irregular kidneys and bilaterally hyperechoic cortices and medullae with a loss of normal corticomedullary distinction. Laparoscopic kidney biopsy revealed a moderate-to-severe chronic interstitial fibrosis with chronic lymphoplasmacytic inflammation, tubular degeneration and atrophy, mild glomerulosclerosis and mild large vascular amyloidosis. Tubular epithelial cell karyomegaly was multifocally evident throughout the kidney. The liver had moderate diffuse zone 1 hepatocellular atrophy, periportal fibrosis, biliary hyperplasia, mild perisinusoidal amyloidosis and hepatocyte karyomegaly in zones 2 and 3. The patient continued to decline and developed polyuria, polydipsia, lethargy and hyporexia irrespective of rigorous management, which failed to curtail the progressive anemia and azotemia. The patient was euthanized 8 months from the onset of clinical signs. RELEVANCE AND NOVEL INFORMATION: Fanconi syndrome in cats is a rare condition, with most reports occurring secondary to chlorambucil treatment. This is the first known case of Fanconi syndrome occurring with concurrent hepatorenal epithelial karyomegaly in a young Sphynx cat.