Late-onset ornithine transcarbamylase deficiency with neurological damage and serial brain multimodality monitoring: a case report.

Background: Late-onset ornithine transcarbamylase deficiency (OTCD) is a rare urea cycle disorder that may present in adulthood with acute hyperammonemic encephalopathy and cerebral edema. The disease has a rapid onset and progression, resulting in high mortality and poor prognosis. Case presentation: This case report describes a patient with late-onset OTCD who presented to the Department of Critical Care Medicine at Chongqing Medical University Second Affiliated Hospital in August 2024. The patient presented with altered consciousness, generalized convulsions, severe hyperammonemia, and diffuse cerebral edema. He received continuous renal replacement therapy (CRRT), ammonia-lowering therapy, mechanical ventilation, antiepileptic treatment, cerebral edema-directed care, and targeted temperature management (TTM). Serial electroencephalography (EEG), transcranial Doppler ultrasonography (TCD), near-infrared spectroscopy (NIRS), and neuroimaging were used to assess neurological status and cerebral physiological changes over time. Although the blood ammonia level normalized early, the patient subsequently developed fluctuations in vital signs. This suggests that, in patients with OTCD, ongoing or progressive brain injury should still be considered even after ammonia levels have returned to the normal range. The results of multimodal neuromonitoring were used together with the clinical status and neuroimaging findings for continuous reassessment. This approach provided bedside information that supported early recognition of clinical changes and adjustment of the treatment strategy. Conclusion: Ornithine transcarbamylase deficiency is rare and remains difficult to diagnose clinically. This case suggests that delayed neurological deterioration may still occur in late-onset OTCD even after biochemical improvement. Multimodal neuromonitoring may provide useful bedside information for individualized neuroprotective management and may help guide treatment adjustment and the differential diagnosis of possible complications.