A Case of Isolated Abnormal Behavior Associated With Vitamin B12 Deficiency.

Vitamin B12 is a water-soluble nutrient found mainly in animal-derived foods. Vitamin B12 deficiency is a common condition, presenting with hematologic and neurologic abnormalities, but rarely presents as isolated psychosis in a young adult. A 28-year-old male patient was brought in for severe agitation and confusion. Laboratory evaluation revealed severe vitamin B12 deficiency (serum vitamin B12 of <73.8 pmol/L) with elevated homocysteine (25.4 umol/L) and methylmalonic acid (0.95 umol/L) levels. The patient received vitamin B12 replacement, after which his confusion and behavioral disturbances improved significantly, and further psychiatric evaluation failed to reveal a primary psychotic or mood disorder. This case highlights the importance of considering vitamin B12 deficiency in patients with isolated neuropsychiatric symptoms, even in the absence of typical macrocytosis, and demonstrates the potential for significant clinical recovery following timely treatment with vitamin supplementation.