Minimum incidence of primary cervical dystonia in a multiethnic health care population.

BACKGROUND: The two existing estimates of the incidence of primary cervical dystonia were based on observations in relatively ethnically homogeneous populations of European descent.
OBJECTIVE: To estimate the minimum incidence of primary cervical dystonia in the multiethnic membership of a health maintenance organization in Northern California.
METHODS: Using a combination of electronic medical records followed by medical chart reviews, we identified incident cases of cervical dystonia first diagnosed between 1997 and 1999.
RESULTS: We identified 66 incident cases of cervical dystonia from 8.2 million person-years of observation. The minimum estimate of the incidence of cervical dystonia in this population is 0.80 per 100,000 person-years. Ethnicity-specific incidence rates were calculated for individuals over age 30. Incidence was higher in white individuals (1.23 per 100,000 person-years) than in persons of other races (0.15 per 100,000 person-years, p < 0.0001). The minimum estimated incidence was 2.5 times higher in women than in men (1.14 vs 0.45 per 100,000 person-years, p = 0.0005). The average age at diagnosis was higher in women (56 years) than in men (45 years, p = 0.0004). There was no significant difference in reported symptom duration prior to diagnosis between women and men (3.9 vs 5.3 years).
CONCLUSION: The estimated incidence of diagnosed cervical dystonia among white individuals in this Northern Californian population is similar to previous estimates in more ethnically homogeneous populations of largely European descent. The incidence in other races, including Hispanic, Asian, and black appears to be significantly lower. The incidence is also higher in women than in men.