Comparison of muscle activation patterns in adductor and abductor spasmodic dysphonia

Patients with adductor and abductor spasmodic dysphonia were compared with normal controls on speech items particularly difficult for the two patient groups. Intrinsic and extrinsic laryngeal muscles were measured during adduction for voicing and for a glottal stop, and during abduction after a vowel and after a glottal stop. Muscle activity was measured while the patients attempted the speech items, with considerable difficulty, but not during periods of complete voice loss. Muscle activity at rest, activity increases for speech, and percent changes for adduction and abduction did not differ from normal in either patient group. The results demonstrated normal muscle activation levels and changes for speech in the patients, and suggested that symptoms occur when spasmodic bursts intrude on an otherwise normal pattern.