Vitamin B12 Deficiency: A Rare Cause of Excessive Daytime Sleepiness

The document described a 71-year-old man with severe vitamin B12 deficiency causing excessive daytime sleepiness (EDS), despite adherence to CPAP therapy for obstructive sleep apnea (OSA). His EDS did not improve with modafinil but resolved completely after vitamin B12 supplementation, significantly improving his Epworth Sleepiness Scale (ESS) score. This case underscored the importance of considering vitamin B12 deficiency in patients with unexplained hypersomnia, even without anemia or macrocytosis.