The prevalence and clinical features of spasmodic dysphonia: A review of epidemiological surveys conducted in Japan

Abstract

Spasmodic dysphonia (SD) is a rare disease and its epidemiological status is unclear. This review aimed to explore the current prevalence and clinical features of SD in Japan. Methods: We reviewed Japanese surveys of SD and compared them to surveys reported from other countries. We focused on SD prevalence, clinical features (SD type, sex and age), and treatment modalities. Results: The SD prevalence in Japan was 3.5-7.0/100,000, similar to that in Rochester (NY, USA) and Iceland. Adductor SD predominated (90-95%) and females were four-fold more likely to be affected than males. Mean age at onset was approximately 30 years in Japan. Several years elapsed from onset to diagnosis. The most frequent treatment was botulinum toxin injection, and surgical intervention, particularly type 2 thyroplasty is becoming more popular. Conclusions: Our review demonstrated some differences of clinical features of SD in Japan compared with other countries, such as a greater female predominance and younger age of onset. Many physicians and patients may be unfamiliar with the clinical features of SD leading to delayed of diagnosis. Therefore, we proposed diagnostic criteria to facilitate early diagnosis and an appropriate choice of treatment modalities.

Botulinum toxin injection into the intrinsic laryngeal muscles to treat spasmodic dysphonia: A multicenter, placebo‐controlled, randomized, double‐blinded, parallel‐group comparison/open‐label clinical trial

“…SD is considered focal dystonia when it affects the larynx, and is sometimes associated with segmental, multifocal, or systemic dystonia [2]. Among all cases of SD, 80% to 95%, and 5% to 17% are of the adductor and abductor type, respectively [3][4][5]. Mixed SD is very rare.…”

“…Mixed SD is very rare. SD likely affects females; the female:male ratio ranges from 1.1:1 to 4.1:1 [2,[4][5][6]. The mean age of onset ranges from 31 to 51 years [2,[5][6][7].…”

“…SD likely affects females; the female:male ratio ranges from 1.1:1 to 4.1:1 [2,[4][5][6]. The mean age of onset ranges from 31 to 51 years [2,[5][6][7]. Regardless of type, SD patients find conversations difficult, which compromises both work and social function.…”

“…BT as an SD treatment has been approved in Australia and some Central and South American countries, but not in the United States, Europe, or Asian countries such as Japan. As a result, many patients were unable to benefit from effective SD therapy in Japan [5]. Therefore, we performed a multicenter, placebo-controlled, randomized, double-blinded, parallel-group comparison/ open-label clinical trial (the BOtulinum toxin Injection therapy for Spasmodic dySphonia [BOISS], study) with the aim of obtaining approval for BT therapy for SD in Japan.…”

Post‐treatment clinical course following botulinum toxin injection therapy for adductor spasmodic dysphonia: Analysis of data from a placebo‐controlled, randomized, double‐blinded clinical trial in Japan

“…Among them, 80‐95% are adductor SD (ADSD) followed by abductor SD (ABSD) and mixed SD. 3 , 4 , 5 In ADSD, intermittent glottal closure blocks expiratory airflow during phonation causing voice breaks, which makes the voice strained and strangled. SD may affect females more, with a 1.1:1 to 4.1:1 female: male ratio.…”