Prevalence of focal dystonias in the western area of Tottori Prefecture in Japan.

We evaluated the prevalence of focal dystonias in the western area of Tottori Prefecture in Japan. The population of the area was 244,935 on October 1, 1992. Because four patients with blepharospasm and three patients with writer's cramp did not visit any hospitals or clinics in 1993 and did not reply to our question letter, we could not confirm their present condition: with or without focal dystonia in 1993. Four patients with facial dystonia including blepharospasm and oromandibular dystonia, seven with spasmodic torticollis, and four with writer's cramp were observed. The prevalence of focal dystonias was 6.12 per 100,000 persons, which may be lower than that in western countries. Although the reasons for this difference are still unclear, a genetic factor may be one implication.