Definition
Fanconi syndrome is a generalised dysfunction of the proximal renal tubule, causing failure to reabsorb multiple solutes that are normally reclaimed there.
What is lost
- Glucose — glycosuria with a normal blood glucose
- Amino acids — generalised aminoaciduria
- Phosphate — hypophosphataemia → osteomalacia/rickets
- Bicarbonate — type 2 (proximal) renal tubular acidosis (a normal anion gap acidosis)
- Urate and potassium — hypouricaemia, hypokalaemia
Causes
- Inherited: cystinosis (commonest in children), Wilson disease, galactosaemia, hereditary fructose intolerance
- Acquired: multiple myeloma, drugs/toxins — tenofovir, ifosfamide, expired tetracyclines, heavy metals (lead, cadmium)
Clinical presentation
- Polyuria and polydipsia
- Bone disease (osteomalacia/rickets) from phosphate wasting
- Features of the acidosis and hypokalaemia (weakness)
- In children, failure to thrive
Management
- Treat the underlying cause (e.g. stop the offending drug, treat myeloma, Wilson disease)
- Replace losses: phosphate, bicarbonate (alkali), potassium and vitamin D
MRCP-specific traps
- Glycosuria with a normal blood glucose is a classic clue to proximal tubular disease.
- Tenofovir and ifosfamide are the drug causes to remember.
- The acidosis is a normal anion gap (type 2 RTA) — link to the anion gap approach.
Summary
Fanconi syndrome is generalised proximal tubular failure, leaking glucose, amino acids, phosphate and bicarbonate (type 2 RTA). Causes include cystinosis, myeloma and drugs (tenofovir, ifosfamide). Treat the cause and replace the urinary losses.
nephrologybiochemistrymrcp part 2