We report a case of involuntary phonation caused by abnormal vocal cord 
movements during expiration in a patient with Parkinson's disease. A 60-year-old 
woman had been treated for parkinsonism at the outpatient clinic of the 
Department of Neurology since August 1999. She began to groan involuntarily in 
the daytime in September 2001. She could not eat well while groaning. Stridor 
was not noted during sleep at night. Endoscopic examination of the larynx 
revealed insufficient abduction of the bilateral vocal cords, although the 
glottis was not so small as to cause stridor during inspiration. During 
expiration, however, the vocal cords adducted, resulting in the involuntary 
production of voice. Electromyography showed an increase in the activity of the 
thyroarytenoid and lateral cricoarytenoid muscles. This muscle activity was 
further enhanced during inspiration. The involuntary phonation disappeared when 
the patient's dose of L-dopa was decreased, although she had a decrease in her 
systemic mobility as well. When the dose of L-dopa was increased to the 
therapeutic level, involuntary phonation recurred, and her voluntary systemic 
activity improved. In the present case, it was considered that excessive 
dopaminergic denervation occurred in the nerve innervating the laryngeal 
adductors. Involuntary voice appeared to be produced by hypertonus of the 
laryngeal adductors because of a lowering in the threshold level for L-dopa, 
even though the drug was administered at the usual dose.