Overview

A constellation of abnormalities caused by defective proximal renal tubular reabsorption of glucose, electrolytes, and amino acids.

Signalment

Signs

• Vary depending on the severity of specific solute losses and whether or not renal failure has developed.
• Loss of amino acids and glucose-usually not associated with clinical signs other than polyuria and polydipsia (most common clinical signs).
• Weight loss, often despite a normal appetite.
• Variable lethargy.
• May have decreased appetite.
• Poor body condition.
• Abnormal growth (rickets) may occur in young animals.

Causes & Risk Factors

• Inherited in basenjis.
• Acquired Fanconi syndrome has been reported in dogs given gentamicin, streptozotocin, maleic acid (experimental), amoxicillin, and chicken jerky treats from China; also reported secondary to primary hypoparathyroidism. Chicken jerky treat ingestion has become an important cause of Fanconi syndrome in the past 5 years. The causative toxin still has not been identified.

Differential Diagnosis

Primary renal glucosuria also causes glucosuria in the absence of hyperglycemia; documentation of aminoaciduria, mild proteinuria, or a hyperchloremic (normal anion gap) metabolic acidosis suggests Fanconi syndrome.

CBC/Biochemistry/Urinalysis

• CBC usually normal.
• Hypokalemia in about one-third of cases.
• Hyperchloremic metabolic acidosis.
• Azotemia if renal failure develops.
• Hypophosphatemia and hypocalcemia may occur in affected young, growing animals.
• Urine specific gravity usually low (1.005–1.018); mild proteinuria common; ketonuria may be present.
• Granular or lipid renal casts and bacteria were seen in 27–40% of dogs that developed proximal renal tubulopathy after eating chicken jerky treats.

Other Laboratory Tests

Hyperchloremic (i.e., normal anion gap) metabolic acidosis due to bicarbonaturia with urine pH <5.5. Urine pH is >6.0 in distal RTA (renal tubular acidosis), and this is a key diagnostic difference between proximal (Fanconi syndrome) and distal RTA. Bicarbonaturia does not occur unless a bicarbonate load is administered.

Imaging

Radiography-young, growing dogs may have features of rickets and angular limb deformities; adult patients may exhibit decreased bone density.

Diagnostic Procedures

Urinary clearance studies to document excessive excretion of solutes such as glucose, amino acids, and electrolytes are needed for confirmation. It is not recommended to test animals <8 weeks of age because false-positive results may occur. A 24-hour urine sample can be sent to the Metabolic Genetic Disease Testing Center (University of Pennsylvania) to screen for aminoaciduria. Fractional reabsorption of amino acids in affected dogs ranges from 50% to 96% (normal range, 97–100%).

Pathologic Findings

Renal papillary necrosis may occur as a late finding. Karyomegaly of the tubular cells has been reported.

Drug(s)

Use potassium citrate (1 mEq = 108 mg) at 50–500 mg/kg q12h (1 to >10 mEq/kg/day; start with a low dosage) or sodium bicarbonate (1 mEq = 84 mg) at 80–300 mg/kg q8–12h (1 to >10 mEq/kg/day; start with a low dosage) as dictated by blood gas and electrolyte data. These are much higher dosages than are necessary in distal RTA.

Contraindications/Possible Interactions

• Avoid drugs that are nephrotoxic or have the potential to cause Fanconi syndrome (see “Causes & Risk Factors”).
• Avoid potassium chloride because affected patients are hyperchloremic.

See Also

• Hypokalemia
• Renal Failure, Acute
• Renal Failure, Chronic

Internet Resources

• Metabolic Genetic Disease Testing Center (University of Pennsylvania): http://research.vet.upenn.edu/penngen/
• Suggested treatment protocol for dogs with idiopathic Fanconi syndrome: http://www.basenji.org/ClubDocs/fanconiprotocol2003.pdf.