Hyperammonaemic encephalopathy and subsequent arthritis due to Ureaplasma urealyticum in a haematopoietic cell transplant recipient: a case report and literature review.

Hyperammonaemic encephalopathy (HE) is a rare but life-threatening complication increasingly linked to disseminated Ureaplasma infection in severely immunocompromised patients. We report a 31-year-old hematopoietic cell transplant (HCT) recipient who developed HE caused by U. urealyticum on day + 11 post-HCT, diagnosed by molecular testing and successfully treated with doxycycline and supportive therapy. Two months later, she developed relapsing septic arthritis with U. urealyticum detected in synovial fluid. Our literature review identified 17 cases of patients with haematological malignancies or cellular therapies and Ureaplasma infection: nine presented with arthritis alone, seven with HE alone, and one developed both manifestations sequentially.