Introduction: Type A botulinum toxin (BT) injection for spasmodic dysphonia (SD) has been covered by insurance since July 2018 in Japan. After insurance adaptation, BT injection was performed for three cases of abductor spasmodic dysphonia (ABSD), and the progress is reported here.

Subjects: We herein report three cases in which ABSD was diagnosed at our hospital and related hospitals and treated with BT injection.

Case 1. A 30-year-old woman had a chief complaint of aphonia and breathlessness for the past 5 years. ABSD was suspected, so BT 5.0 units were injected into the left posterior cricoarytenoid muscle (PCA) using an electromyogram (EMG). At a re-examination three weeks later, the vocal cords has only opened to the middle position. The treatment was deemed effective for PCA but did not improve the symptoms.

Case 2. A 27-year-old woman had a chief complaint of voice loss from 2 months earlier. Suspecting ABSD, BT 5.0 units were injected into the left PCA using an EMG. One month after the injection, the vocal cords has only opened to the middle. The treatment was deemed effective for PCA but did not improve the symptoms.

Case 3. A 57-year-old man had a chief complaint of difficuly vocalizing for the past 8 years. No improvement had been observed despite voice therapy at another hospital for the past three years. ABSD was suspected, so BT 5.0 units were injected into the left PCA using an EMG. One month after the injection, the vocal cords has only opened to the middle. The treatment was deemed effective for PCA but did not improve the symptoms.

Discussion: ABSD accounts for about 5% of SD cases. However, the number of injection cases at our hospital was 1.6%, which was less than in previous reports.

The treatment of ABSD by 5.0 units BT injection to the unilateral PCA conforms to Japanese insurance practice. However, it must be confirmed that the vocal cords on the opposite side move sufficiently, as when the vocal cords on the injection side do not move due to the drug, poor movement of the vocal cords on the opposite side can cause wheezing and dyspnea.

However, the domestic phase 2/3 study included only two ABSD cases, and the effectiveness of this strategy was observed in only one case. In international literature, there have been reports that the efficacy of unilateral administration ranges from insufficient to sufficient in 20% of cases, while bilateral administration has reached 89% efficacy. In the future, bilateral administration of BT should be considered as a treatment for ABSD in Japan.