A 43-year-old male patient with idiopathic Parkinson disease, on dopaminergic
therapy, was admitted with confusion and agitation, diaphoresis, and hyperkinesia
after the commencement of the serotonin-noradrenaline reuptake inhibitor
venlafaxine 2 weeks prior for depression. He was found to have severe
rhabdomyolysis and developed acute renal failure. The most likely diagnosis was
serotonin syndrome induced by venlafaxine, although neuroleptic malignant
syndrome was also considered. The differential diagnosis, atypical features in
this presentation, and possible mechanisms are discussed.