Spasmodic dysphonia

Spasmodic dysphonia (SD) is a focal laryngeal dystonia characterized by involuntary, action-induced spasms of the muscles controlling vocal fold motion. The laryngeal adductor muscles (lateral cricoarytenoid [LCA], interarytenoid, and possibly the cricothyroid and thyroarytenoid [TA]), abductor muscle (posterior cricoarytenoid [PCA]), or rarely both groups of muscles may be affected. Adductor SD is characterized by a harsh, strangled, or effortful voice (glottal fry) with irregular phonatory breaks secondary to vocal fold hyperadduction or spasm. The supraglottic structures may be hyperfunctional as well. Abductor SD presents as a breathy, effortful, hypophonic voice with irregular breaks following consonant voicing secondary to vocal fold hyperabduction. Although the exact etiology of SD is unclear, SD is now recognized as a neurological disorder of central processing.