Distal renal tubular acidosis due to primary hyperparathyroidism

To present 4 cases of distal renal tubular acidosis (RTA) in patients with primary hyperparathyroidism (PHPT) and discuss their possible etiopathogenetic correlation.

We diagnosed distal RTA in 4 patients with symptomatic primary PHPT on the basis of the baseline biochemical variables and the results of the ammonium chloride loading test. Complete resolution of distal RTA was documented after surgical cure of PHPT by removal of a parathyroid adenoma.

All our patients presented with symptomatic bone disease and metabolic myopathy. One patient presented with recurrent renal stones. Inappropriately alkaline fasting urine (pH >5.5) in association with a normal anion gap metabolic acidosis suggested the diagnosis of distal RTA. All cases were confirmed by an ammonium chloride loading test. Three patients responded to surgical cure of PHPT by normalization of the acid-base status.

Hypercalciuria in PHPT can lead to nephrocalcinosis and renal tubular dysfunction, which manifests as distal RTA. Cure of distal RTA after surgical treatment of PHPT establishes PHPT as the primary cause of distal RTA in these cases.