Hyperammonaemia Presenting as an Acute Neuropsychiatric Syndrome in an Elderly Patient: A Diagnostic Challenge

Hyperammonaemia is a metabolic derangement characterised by elevated circulating ammonia levels resulting in neurotoxicity and a wide spectrum of neurological manifestations.In adults, particularly the elderly, the clinical presentation may be nonspecific and frequently mimics primary psychiatric or neurodegenerative disorders, leading to delays in diagnosis and management.We report the case of a 77year-old male patient who presented with progressive neuropsychiatric symptoms initially attributed to alcohol use disorder and psychiatric illness.Despite multiple diagnostic investigations and empirical treatment for several suspected etiologies at the initial hospital, the patient's neurological condition continued to deteriorate.The assessment was further complicated by the presence of an acute infarct in the left capsuloganglionic region on the brain MRI.Due to continued clinical deterioration, the patient was transferred to another tertiary care facility for further evaluation and management.After a thorough review of the clinical course and prior investigations of the patient, the treating physician advised serum ammonia estimation, considering the possibility of an underlying metabolic cause of encephalopathy.The investigation revealed a markedly elevated serum ammonia concentration of 497.7 µg/dL (reference range: 27.2-102 µg/dL), supporting the diagnosis of hyperammonaemia-associated encephalopathy.Following the initiation of ammonia-lowering treatment, the patient showed significant clinical improvement.This case highlights the importance of considering metabolic causes, including hyperammonaemia, in patients presenting with unexplained neuropsychiatric symptoms, as early recognition may facilitate timely management and improve clinical outcomes.