Clinical Reasoning: A Young Adult Man With Cognitive Changes, Gait Difficulty, and Renal Insufficiency

A 22-year-old right-handed man with recently diagnosed gout and renal insufficiency presented with 3 months of progressive gait instability and cognitive changes. He initially presented to an outside institution and underwent a broad workup, but an etiology for his symptoms was not found. On subsequent presentation to our institution, his examination revealed multidomain cognitive dysfunction, spasticity, hyperreflexia, and clonus. A broad workup was again pursued and was notable for an MRI of the brain, revealing cortical atrophy advanced for his age, bland CSF, and a weakly positive serum acetylcholine receptor ganglionic neuronal antibody of unclear significance. The history of gout and inadequately explained renal insufficiency led to a workup for inborn errors of metabolism, including urine amino acid analysis, which revealed a homocysteine peak. This finding prompted further evaluation, revealing markedly elevated serum homocysteine and methylmalonic acid and low methionine. He ultimately developed superficial venous thromboses, a segmental pulmonary embolism, and clinical and electrographic seizures. He was initiated on appropriate treatment, and his symptoms markedly improved. The case serves as a reminder to include late-onset inborn errors of metabolism in the differential for young adult patients with onset of neurologic, psychiatric, renal, and thromboembolic symptoms.