Neuroleptic malignant syndrome

A 23-year-old man is brought to the emergency department after collapsing at a music festival on a hot summer day. The patient was with friends at an electronic dance show. According to his friends, the patient consumed a powdered drug at the concert. Afterwards, while dancing, he suddenly collapsed and started having tremors in the upper and lower extremities. He has a past medical history of depression, anxiety, and bipolar disorder, for which he takes fluoxetine, alprazolam as needed, and aripiprazole. Temperature is 39.0°C (102.2 °F), pulse is 132/min, respirations are 24/min, blood pressure is 172/85 mmHg, and O2 saturation is 97% on room air. On physical examination the patient is diaphoretic, mumbling incoherent sounds, and will not lie still in the gurney. The patient has increased muscle tone. Brief, sudden jerks are present throughout the upper and lower extremities. Which of the following clinical features is most specific to this patient's clinical presentation?