Severe Nonhepatic Hyperammonemia Associated With Ureaplasma parvum and Mycoplasma hominis Infection in a Dually Immunosuppressed Woman Presenting As Suspected Peritoneal Carcinomatosis.

Severe nonhepatic hyperammonemia is a rare but potentially life-threatening condition in immunocompromised patients. Ureaplasma and Mycoplasma species are fastidious urogenital organisms that generate ammonia and may cause disseminated, culture-negative infection. We report the case of a 63-year-old woman receiving dual biologic therapy, ocrelizumab for multiple sclerosis and secukinumab for psoriasis, who presented with a history of sterile pyuria and lower urinary tract symptoms. Within two months, her condition progressed to polyserositis, paralytic ileus, multiorgan dysfunction, and metabolic encephalopathy requiring admission to intensive care. Imaging suggested a left ovarian neoplasm with peritoneal carcinomatosis, prompting exploratory laparotomy, which ultimately revealed diffuse seropurulent pachyperitonitis and a small localized purulent collection, without evidence of malignancy. Plasma ammonia rose despite the absence of hepatic failure, causing severe encephalopathy requiring continuous renal replacement therapy (CRRT). Conventional cultures of urine, blood, ascitic fluid, vaginal exudate, and peritoneal specimens were repeatedly negative, prompting investigation for unusual organisms. Urine polymerase chain reaction ultimately detected Ureaplasma parvum and Mycoplasma hominis. Plasma ammonia remained dependent on CRRT, with recurrent rebound following interruptions before targeted antimicrobial therapy was established. Following treatment with levofloxacin and doxycycline, sustained metabolic control allowed discontinuation of CRRT without further rebound hyperammonemia. The temporal pattern, while occurring alongside surgical drainage and peritoneal lavage, supports targeted treatment of the presumed underlying invasive infection as an important component of recovery. This case highlights the importance of considering fastidious urogenital organisms in immunosuppressed patients with unexplained nonhepatic hyperammonemia and persistently negative conventional cultures, particularly when ammonia levels remain dependent on extracorporeal clearance.