What are the hallmark symptoms associated with Neuroleptic Malignant Syndrome (NMS)?

Neuroleptic Malignant Syndrome (NMS) is a serious and potentially life-threatening reaction typically associated with the use of antipsychotic medications. The hallmark symptoms of NMS prominently include severe muscle rigidity and a high fever. Muscle rigidity is characterized by a significant increase in muscle tone, leading to stiff movements, and is often described as "lead-pipe" rigidity. The elevated body temperature, or fever, is often noted to be above 38 degrees Celsius (100.4 degrees Fahrenheit) and can rise to dangerous levels.

These symptoms stem from the dopamine blockade caused by neuroleptic medications—that can lead to dysregulation of thermoregulation and increased muscle contraction. NMS can also include other symptoms like altered mental status, autonomic instability, and metabolic changes, but the combination of muscle rigidity and fever is definitive in identifying this syndrome. Understanding these core symptoms is crucial for timely diagnosis and management, as NMS requires immediate medical attention.

The other options involve symptoms that do not align with the core presentation of NMS, making them less relevant to diagnosing this serious condition.