Neuroleptic Malignant Syndrome (NMS)
This patient most likely has Neuroleptic Malignant Syndrome (NMS), a life-threatening emergency caused by the combination of antipsychotic medications (olanzapine and risperidone). The presentation of fever and rigidity in a patient on multiple antipsychotics is classic for NMS, even with normal reflexes 1, 2.
Why NMS is the Primary Diagnosis
The combination of:
- Fever (disruption of body temperature regulation)
- Rigidity (muscle rigidity from central dopamine blockade)
- Multiple antipsychotic exposure (olanzapine + risperidone)
This triad strongly indicates NMS 1, 2. The FDA label for Risperdal explicitly warns that NMS "manifests as muscle rigidity, generating fever" and is "strongly associated with antipsychotic neuroleptic medications" 1, 2. Normal reflexes do not exclude NMS—the syndrome primarily causes rigidity through central mechanisms, not necessarily altered reflexes 1.
Critical Distinguishing Features
NMS vs. Serotonin Syndrome: While this patient is on sertraline (an SSRI), serotonin syndrome typically presents with hyperreflexia and clonus, not normal reflexes 1. The guideline states serotonin syndrome "may be confused with neuroleptic malignant syndrome, but it is a distinct entity" with excessive 5-HT1A receptor stimulation 1. The normal reflexes and prominent rigidity favor NMS over serotonin syndrome.
Atypical presentations are common: Recent evidence shows that second-generation antipsychotics like risperidone and olanzapine can cause NMS with delayed or atypical features. One case report documented NMS from risperidone where "fever did not occur until hospital day 2" and the patient "never remained febrile for more than 24 hours" 3. Olanzapine alone has been reported to cause isolated fever even without complete NMS 4, 5.
Additional Diagnostic Considerations
Check for:
- Elevated creatine phosphokinase (CPK/CK) - typically markedly elevated in NMS 1, 3
- Leukocytosis - common but not universal 3
- Diaphoresis, altered mental status, autonomic instability - other NMS features 1, 3
- Tachycardia - frequently present 1
Why Drug Fever is Less Likely
While drug-induced fever is possible with any medication 1, the presence of rigidity makes this diagnosis insufficient. Simple drug fever does not cause muscle rigidity—this combination specifically points to NMS 1, 2.
Immediate Management Priority
Stop all antipsychotic medications immediately 6. A 2023 case report emphasized: "All antipsychotic and sedative drugs...were discontinued, after which the patient showed significant clinical improvement" 6. The guideline confirms that NMS requires recognition that "withdrawal of certain drugs may be associated with fever" but the priority is stopping the causative agents 1.
Common Pitfall
Do not wait for "complete" NMS criteria. Clinicians should "consider NMS in afebrile patients presenting with diaphoresis, changes in level of consciousness, mutism, tremors, tachycardia, leukocytosis, and elevated CK levels" 3. The presence of fever plus rigidity in a patient on multiple antipsychotics is sufficient to act.
The FDA label explicitly states: "Disruption of body temperature regulation has been attributed to antipsychotic agents" and "Neuroleptic malignant syndrome...manifests as muscle rigidity, generating fever" 2. With this patient on both olanzapine and risperidone, the risk is compounded.