Neuroleptic malignant syndrome caused by atypical antipsychotic drugs may present in an atypical manner without symptoms such as hyperthermia and/or muscle rigidity. A detailed description of atypical neuroleptic malignant syndrome induced by atypical antipsychotic drugs, practical information to distinguish neuroleptic malignant syndrome from other related conditions, and the diagnostic criteria that may be used to settle the diagnosis of atypical neuroleptic malignant syndrome are highlighted in this paper. This study was conducted searching PubMed and Science Direct, resulting in 525 articles. 26 case reports that met inclusion criteria were identified. Atypical neuroleptic malignant syndrome was found to develop mainly in male patients suffering from schizophrenia (14 cases) and bipolar disorder (2), and was induced by clozapine (6 cases), olanzapine (5 cases), aripiprazole and quetiapine (4 cases). Muscle rigidity did not develop in patients treated with clozapine and quetiapine, whereas a lack of hyperthermia was common with aripiprazole and clozapine treatment. Atypical neuroleptic malignant syndrome is a difficult matter, especially when symptoms of hyperthermia or muscle rigidity is lacking, but using Levenson's or Adityanjee and Aderibigbe's criteria may increase it detectability, can permit earlier intervention and prevent development of life-threatening typical neuroleptic malignant syndrome.
Keywords: Atypical neuroleptic malignant syndrome; atypical antipsychotic drugs; hyperthermia; muscle rigidity; schizophrenia.