Overview
Definition
A defect in proximal tubule bicarbonate reabsorption, leading to hyperchloremic metabolic acidosis, with preserved urine acidification capacity in severe acidosis.
Epidemiology
Associated with Fanconi Syndrome (generalized proximal tubule dysfunction) in children and adults.
Etiology & Risk Factors
- Impaired HCO3- reabsorption in proximal convoluted tubule
- Associated with multiple myeloma, light chain deposition, amyloidosis, Tenofovir, and Wilson's disease
Clinical Symptoms
- Muscle weakness
- Rickets / Osteomalacia
- Dehydration episodes
Clinical Approach
Diagnosis
- Normal anion gap metabolic acidosis
- Urine pH initially > 5.5, but can drop < 5.5 during severe systemic acidosis
- Hypokalemia
- Glycosuria, phosphaturia, aminoaciduria (Fanconi syndrome)
Management
- High doses of oral bicarbonate/citrate (since much is excreted)
- Thiazide diuretics (to volume-deplete and increase proximal reabsorption)
Complications
- Osteomalacia
- Osteopenia
- Electrolyte imbalances