Which of the following is a sign of neuroleptic malignant syndrome?

• A. Muscle rigidity
• B. Rash
• C. Nasal congestion
• D. Hypoglycemia

Answer: (A)

Muscle rigidity is a hallmark of neuroleptic malignant syndrome, which results from potent dopamine D2 receptor blockade by antipsychotic medications. The rigidity is typically severe and generalized (often described as lead-pipe rigidity) and is accompanied by hyperthermia, autonomic instability, and altered mental status. This combination makes muscle rigidity the most distinctive sign among the options. The other signs—rash, nasal congestion, and hypoglycemia—do not characterize NMS and point to other processes (rash suggests an allergic or dermatologic issue, nasal congestion is nonspecific, and hypoglycemia involves metabolic disturbances not typical of NMS). Recognizing rigidity early prompts immediate actions: stop the offending antipsychotic, provide supportive care, manage hyperthermia and autonomic symptoms, and consider treatments like dantrolene or bromocriptine if indicated.