Hyperammonemic Encephalopathy: A Rare Presentation of Relapsed Multiple Myeloma.

Hyperammonemia is a rare cause of encephalopathy in multiple myeloma in the absence of hepatic involvement. This is the only reported case of a 74-year-old man who presented with multiple myeloma and achieved complete remission but developed hyperammonemia afterward. He was aggressively treated with a combination of chemotherapy and immunotherapy, with a resolution of his encephalopathy; however, within one month, he relapsed with encephalopathy. He ultimately decided to pursue comfort-care measures. The authors conclude that hyperammonemia in multiple myeloma is a rare but important differential in patients with encephalopathy of unknown causes. Aggressive treatment is of the utmost importance due to the high mortality associated with the condition.