A client receiving Risperidone (Risperdal) reports severe muscle stiffness at 10:30 am. By noon, the patient is diaphoretic, drooling, and has difficulty swallowing. By 4:00 pm, vital signs are body temperature, 102.8deg F; pulse, 110 beats/min; respirations, 26 breaths per minute; and blood pressure, 150/90 mm Hg. Select the nurse's best analysis of this scenario.

Neuroleptic malignant syndrome (NMS) is a life-threatening reaction to antipsychotic medications such as risperidone. The classic tetrad includes hyperthermia, severe muscle rigidity (lead-pipe rigidity), autonomic instability, and altered mental status. This client's progression from severe muscle stiffness to diaphoresis, drooling, dysphagia, fever of 102.8°F, tachycardia at 110 beats/min, tachypnea at 26 breaths/min, and hypertension at 150/90 mmHg perfectly matches the NMS presentation. The temporal progression over hours, beginning with rigidity and advancing to autonomic dysregulation, is the hallmark pattern. Serotonin syndrome is incorrect because it typically follows serotonergic agents and features hyperreflexia and clonus rather than profound rigidity; it also usually involves agitation and tremor. Agranulocytosis is a dangerous drop in white blood cells associated with clozapine, not risperidone, and presents with infection signs rather than the neuromuscular and autonomic findings seen here. Tardive dyskinesia involves involuntary repetitive movements — particularly orofacial — that develop after long-term antipsychotic use; it does not cause fever, autonomic instability, or dysphagia. Recognizing NMS promptly is critical because treatment requires immediate discontinuation of the antipsychotic, supportive care, and often administration of dantrolene or bromocriptine to reverse the syndrome before it becomes fatal.