Olanzapine-associated neuroleptic malignant syndrome: Is there an overlap with the serotonin syndrome?

This retrospective phenomenological study aims to examine the seventeen reported olanzapine – induced neuroleptic malignant syndrome cases under the light of possible overlap between neuroleptic malignant syndrome and serotonin syndrome clinical features.The serotonin syndrome clinical features most often reported in cases initially diagnosed as neuroleptic malignant syndrome are: fever (82%), mental status changes (82%) and diaphoresis (47%). Three out of the ten classical serotonin syndrome clinical features were concurrently observed in eleven (65%) patients and four clinical features were observed in seven (41%) patients.The results of this study show that the clinical symptoms of olanzapine-induced neuroleptic malignant syndrome and serotonin syndrome are overlapping suggesting similarities in underlying pathophysiological mechanisms.The neuroleptic malignant syndrome (NMS) is a rare but potentially fatal condition associated with antipsychotic medication. It is mainly characterized by fever, extrapyramidal symptoms, autonomic instability and an altered state of consciousness. It is primarily caused by dopamine (D2) receptors blockage in the nigrostriatal tract, mesocortical pathway and hypothalamic nuclei [1]. Recently, many authors have expressed the view that NMS is not caused by dopamine block alone. Other aminergic systems have also been implicated such as serotonin, norepinephrine, GABA e.t.c. [1,2]. There are controversies as to whether atypical antipsychotics can cause "classical" forms of NMS [3-5].During the last years, a condition of serotoninergic hyperstimulation called "serotonin syndrome" (SS) has been described. It is mainly associated with administration of antidepressive medication. The most frequent clinical features of this syndrome are changes in mental status, restlessness, myoclonus and hyperreflexia [6].The difficulty of differentiating between NMS and SS has been well recognized [7,8].Olanzapine is an atypical antipsychotic, which exhib