A rare case of neuroleptic malignant syndrome without elevated serum creatine kinase

Neuroleptic malignant syndrome (NMS) is a life-threatening adverse reaction to antipsychotic drugs. Although there is no specific examination able to diagnose NMS, serum creatine kinase (CK) elevation has been reported in over 90% of NMS patients. In this report, we describe a patient who developed NMS but had normal CK levels. The patient presented with hyperthermia of over 38°C, severe muscle rigidity, autonomic dysfunction, and altered mental status. Although serum CK levels were measured three times during the course of NMS, the levels were within the normal range. The patient died of respiratory failure 13 days after the onset of NMS symptoms. As patients without elevated serum CK levels are rarely reported, we discuss potential reasons why the serum CK was not elevated in our patient. This case shows clinicians that although serum CK elevation is a useful indicator for the early detection of NMS, the diagnosis of NMS must be determined by clinical symptoms as otherwise, the appropriate treatment procedures for NMS may be delayed.