Hyperammonemic Encephalopathy Caused by Obstructive Urinary Tract Infection Due to Urease-Positive Corynebacterium riegelii in an Elderly Woman: A Case Report

Hyperammonemia typically results from hepatic dysfunction, but obstructive urinary tract infection (UTI) caused by urease-producing bacteria can rarely induce severe hyperammonemia and encephalopathy. We describe a 76-year-old woman with chronic voiding dysfunction who presented with fever and coma, with a markedly elevated serum ammonia level of 380 μg/dL despite normal liver function. Urinalysis revealed markedly alkaline urine and pyuria. Head computed tomography (CT) and magnetic resonance imaging showed no acute abnormalities. Abdominal CT demonstrated marked bladder distention and no findings suggestive of chronic liver disease. Bladder decompression and piperacillin/tazobactam therapy led to rapid improvement, with ammonia falling to 70 μg/dL and full recovery of consciousness within 48 hours. Urine culture later yielded <i>Corynebacterium</i> species, prompting the addition of vancomycin; the organism was subsequently identified as urease-positive <i>Corynebacterium</i> <i>riegelii</i>. Blood cultures remained negative, and a later plasma amino acid analysis showed no evidence of urea-cycle disorders. The patient had no recurrence of hyperammonemia or UTI during the four-year follow-up. Obstructive UTI due to urease-producing bacteria should be recognized as a reversible cause of acute encephalopathy in elderly patients with urinary retention.