Atypical Neuroleptic Malignant Syndrome without Hyperthermia or Rigidity in the Intensive Care Unit: A Diagnostic Challenge

Abstract

Neuroleptic malignant syndrome (NMS) is a potentially life-threatening condition associated with dopamine antagonist medications. Although the classical presentation includes hyperthermia, generalized rigidity, autonomic instability, and altered mental status, atypical forms lacking these features may occur and complicate diagnosis. We report a case most consistent with atypical NMS in a 76-year-old patient who developed acute delirium and intermittent paratonia without fever or sustained rigidity following antipsychotic exposure. The clinical course was characterized by marked autonomic instability and a transient elevation of creatine kinase, peaking early and subsequently normalizing. A temporal relationship between antipsychotic exposure, symptom onset, and laboratory findings supported the diagnostic consideration. Although clinical improvement was observed following dopaminergic therapy, this finding was interpreted cautiously given potential confounding factors. This case highlights that NMS may occur without fulfilling classical diagnostic criteria and underscores the importance of integrating clinical, laboratory, and temporal features, particularly in critically ill patients.