What is the classic neurological feature of neuroleptic malignant syndrome?

Neuroleptic malignant syndrome (NMS) is a potentially life-threatening condition often associated with the use of antipsychotic medications (neuroleptics). The classic neurological feature of NMS is muscle rigidity. This rigidity is often described as "lead-pipe" rigidity, where the muscles are very stiff and unyielding. It can be profound and is a key symptom that may help differentiate NMS from other conditions.

The presence of muscle rigidity in NMS is usually accompanied by autonomic instability, altered mental status, and hyperthermia, but the rigidity stands out as a hallmark neurological sign. This is critical for diagnosis and management, as it helps clinicians identify NMS early, allowing for prompt intervention and reduction of antipsychotic medications.

Other symptoms such as anxiety, seizures, or drowsiness can occur in various medical conditions but are not specific to or characteristic of NMS. While altered mental status (which may include drowsiness or confusion) may occur, muscle rigidity remains the definitive and distinguishing neurological feature of this syndrome.