Hyporeninemic hypoaldosteronism in a patient with multiple myeloma

A patient with progressive renal failure due to multiple myeloma presented with a mixed acid-base disorder (non-anion gap acidosis and respiratory alkalosis) with persistent severe hyperkalemia. Studies revealed an intact ability to lower urine pH during acid loading, markedly decreased plasma renin and aldosterone concentrations despite volume depletion, and an inappropriately low fractional excretion of potassium. Renal biopsy demonstrated plasma cell infiltration of the renal interstitium and typical proteinaceous intratubular casts. Both proximal and distal renal tubular acidification defects have been described previously in patients with multiple myeloma, but this is the first report of hyporeninemic hypoaldosteronism, hyperkalemia, and hyperchloremic metabolic acidosis in association with renal involvement in multiple myeloma.