[Clinical and neurochemical aspects of diaphragmatic myoclonus]

The case of a 35-year-old woman with diaphragmatic myoclonus of four year duration is presented. The myoclonus deteriorated with anxiety, menstruation and orthostatism. It was frequently accompanied by urinary retention or incontinence. Several pharmacologic agents were shown to be ineffective until the myoclonus was suppressed with a combination of gabapentin and tiagabine. In this article, the respiratory center is proposed as the original focus of the myoclonus, a deficit of gamma-aminobutyric acid (GABA) in brainstem structures as its neurochemical substrate, and GABAergic enhancement as an effective therapeutic measure. The clinical manifestations, etiology, ancillary studies and treatment of diaphragmatic myoclonus are reviewed. Experimental evidence on the anatomical localization, physiology and neurochemistry of the respiratory center is examined. The authors try to relate some of the patient's clinical findings to the experimental data found in the medical literature. The action mechanisms of gabapentin and tiagabine are examined and these drugs are proposed as effective means of enhancing GABAergic neurotransmission and treating diseases with increased inspiratory drive.