Atypical neuroleptic malignant syndrome associated with olanzapine.

Neuroleptic malignant syndrome (NMS) is a potentially life-threatening adverse effect of antipsychotic agents. It generally is characterized by fever, altered mental status, rigidity, and autonomic dysfunction. A 53-year-old man developed NMS without rigidity while taking olanzapine. Such atypical cases may support either a spectrum concept of NMS or the theory that NMS secondary to atypical antipsychotics differs from that caused by conventional neuroleptics. More flexible diagnostic criteria than currently mandated by the the Diagnostic and Statistical Manual of Mental Disorders, Fourth Revision, may be warranted.