The combination of both abductor (AB) and adductor (AD) vocal cord spasms in a person who has spasmodic dysphonia (SD). Most individuals with SD have a predominance of one spasm type or the other—AB or AD—such that we classify the person as having either “AB-SD” or “AD-SD.” Some individuals, however, have a significant amount of both types of spasms. That is, a person experiences phonatory arrests or squeezedowns caused by AD spasms, followed suddenly by dropouts to a whisper caused by AB spasms. This kind of person is described as having “mixed AB-AD spasmodic dysphonia.”
Treatment for SD usually involves two-muscle Botox injections: for AD-SD, injecting into both of the thyroarytenoid muscles; for AB-SD, into both of the posterior cricoarytenoid muscles. Treatment for mixed AB-AD SD usually begins with the two muscles causing spasms of which the patient is most aware; if the results are not satisfactory (often because the untreated kind of spasms come to the fore without competition from the other kind of spasms), some of these patients are then eventually treated with four-muscle injections.