[Neuroleptic malignant syndrome in a patient with polyneuropathy: mechanism of muscle rigidity and elevated serum creatine kinase levels].

A 49-year-old man was admitted with the chief complaints of muscle weakness and gait disturbance. His neurological examination was compatible with peripheral neuropathy, and laboratory tests revealed IgA monoclonal gammopathy, increased protein content in the cerebrospinal fluid (CSF) without pleocytosis, and slow motor and sensory nerve conduction velocity. He was diagnosed as having chronic inflammatory demyelinating polyneuropathy with IgA monoclonal gammopathy of undetermined significance. The patient was treated with steroid, and plasmapheresis. He became so restless that antidepressant and haloperidol were administered. Then, he became unresponsive, and developed high fever, sweating, tachycardia, and tremor. Examination of CSF showed increased 3-methoxy-4-hydroxy-phenylglycol and decreased homovanillic acid. He was diagnosed as having neuroleptic malignant syndrome (NMS). However, his muscle tonus was still flaccid in his lower extremities that had been suffered from chronic polyneuropathy. Interestingly, his serum creatine kinase (CK) content was only slightly elevated. We suppose that the pathophysiological location of NMS might be primarily central, and that muscle rigidity and elevation of serum CK might not occur, if the peripheral nerves were completely impaired.