Disinhibitory abnormal behavior induced by treatment of Parkinson disease

The treatment of Parkinson disease has considerably progressed in the last 20 years. However, such treatments results in the adverse event of disinhibitory abnormal behavior, which includes impulse control disorders, punding, and dopamine dysregulation syndrome. Pathological gambling is the most extensively studied among such abnormal behaviors. It has been associated with the use of dopamine agonists and its prevalence increases according to the does of the drugs. The maximum dose of the ergot dopamine agonist pergolide is 1.25 mg/day in Japan, which is a quarter of that used in Western countries. The maximum dose of the non-ergot dopamine agonist, pramipexole is 4.5 mg/day in Japan, which is the same as in Western countries. Pramipexole was launched in 2004 in Japan, and since then cases of pathological gambling associated with dopamine agonists used has been increasing. Because of the excellent health-care system in Japan, patients can easily acquire expensive dopamine agonists. Although the prevalence of these abnormal behaviors has not been studied in Japan, it could be highly proportionate to the amount of dopamine agonists. Disinhibitory abnormal behavior is also induced by deep brain stimulation of the subthalamic nucleus. This technology was approved in 2000 in Japan. The mechanisms by which these behaviors are induced are different between dopamine replacement therapy and deep brain stimulation. Parkinson disease patients and their caregivers occasionally believe the disinhibitory abnormal behavior as arising from the original personality of the patient rather than as an adverse event of treatment. Neurologists should be aware of the occurrence of disinhibitory abnormal behavior in the clinical practice.