A patient on an inpatient psychiatric unit presents with a sudden high fever. The nurse suspects neuroleptic malignant syndrome because the patient also has the following symptoms:

Choice A reason: Elevated liver function tests may occur with various medications but are not specific to NMS. They do not help confirm the diagnosis and may distract from more critical signs. Choice B reason: Lead pipe rigidity (uniform resistance to passive movement) and autonomic instability are classic features of NMS. These symptoms, along with hyperthermia and altered mental status, confirm the diagnosis and require immediate intervention. Choice C reason: Increased intracranial pressure and headache are not part of the NMS symptom profile. These signs suggest other neurological conditions and would mislead the clinical assessment. Choice D reason: Agranulocytosis is a hematologic emergency linked to clozapine, not antipsychotics broadly. It involves infection risk due to neutropenia, not muscular or autonomic symptoms.