Atypical neuroleptic malignant syndrome presenting as fever of unknown origin in the elderly.

A 79-year-old nursing home resident who was taking olanzapine presented to multiple hospitals with fevers of unknown origin. After an extensive workup to rule out infection, the patient was diagnosed as having neuroleptic malignant syndrome (NMS). This patient's presentation was atypical because of the lack of rigidity or tremor at the time of admission. This case highlights the importance of including NMS in the differential diagnosis of fever of unknown origin in medical patients. A review of the medical literature is taken, focusing on diagnoses, prevalence, predisposing factors, pathophysiology, and current treatment approaches for NMS.