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

From the Parkinson’s Institute (C.M., C.M.T.), Sunnyvale; Northern California Kaiser Permanente Medical Care Plan (S.K.V.d.E., R.D.F., K.S.B.-A., J.K., A.D.L., N.R., A.J.K., A.L.B.), Oakland; University of California–San Francisco (N.R.); Department of Health Research and Policy (L.M.N.), Stanford University, Palo Alto, CA; and Morton and Gloria Shulman Movement Disorders Centre (C.M.), Toronto Western Hospital, and Department of Medicine, University of Toronto, Ontario, Canada.

Address correspondence and reprint requests to Dr Tanner, Parkinson’s Institute, 1170 Morse Ave., Sunnyvale, CA 94089 ctanner{at}thepi.org

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.

Supported in part by the following sources: grants from the Dystonia Medical Research Foundation and NIH 1 RO1 NS046340 to Dr. Tanner and a CIHR clinical research training award and a Parkinson Society of Canada clinical research fellowship to Dr. Marras.

Disclosure: The authors report no conflicts of interest.

Received May 22, 2006. Accepted in final form March 15, 2007.