Descriptive epidemiology of cervical dystonia

Abstract

Background: Cervical dystonia (CD), the most common form of adult-onset focal dystonia, has a heterogeneous clinical presentation with variable clinical features, leading to difficulties and delays in diagnosis. Owing to the lack of reviews specifically focusing on the frequency of primary CD in the general population, we performed a systematic literature search to examine its prevalence/incidence and analyze methodological differences among studies.

Methods: We performed a systematic literature search to examine the prevalence data of primary focal CD. Sixteen articles met our methodological criteria. Because the reported prevalence estimates were found to vary widely across studies, we analyzed methodological differences and other factors to determine whether true differences exist in prevalence rates among geographic areas (and by gender and age distributions), as well as to facilitate recommendations for future studies.

Results: Prevalence estimates ranged from 20-4,100 cases/million. Generally, studies that relied on service-based and record-linkage system data likely underestimated the prevalence of CD, whereas population-based studies suffered from over-ascertainment. The more methodologically robust studies yielded a range of estimates of 28-183 cases/million. Despite the varying prevalence estimates, an approximate 2:1 female:male ratio was consistent among many studies. Three studies estimated incidence, ranging from 8-12 cases/million person-years.

Discussion: Although several studies have attempted to estimate the prevalence and incidence of CD, there is a need for additional well-designed epidemiological studies on primary CD that include large populations; use defined CD diagnostic criteria; and stratify for factors such as age, gender, and ethnicity.

Keywords: Cervical dystonia; epidemiology; incidence; prevalence.

Conflict of interest statement

Financial disclosures: G.D. has received honoraria for services as a consultant for GlaxoSmithKline, Novartis, and UCB Pharma. J.J. has received honoraria for services as a consultant or an advisory committee member from Allergan, Inc.; Auspex Pharmaceuticals, Inc.; EMD Serono; Lundbeck, Inc.; Merz Pharmaceuticals; the Michael J. Fox Foundation for Parkinson Research; Neurocrine Biosciences; Neurotoxin Institute; and Teva Pharmaceutical Industries, Ltd. He has also received research support from Allergan, Inc.; Allon Therapeutics; Biotie Therapies, Inc.; Ceregene, Inc.; CHDI Foundation; Chelsea Therapeutics; Diana Helis Henry Medical Research Foundation; EMD Serono; the Huntington's Disease Society of America; the Huntington Study Group; Impax Pharmaceuticals; Ipsen Limited; Lundbeck, Inc.; the Michael J Fox Foundation for Parkinson Research; Medtronic; Merz Pharmaceuticals; the National Institutes of Health; the National Parkinson Foundation; Neurogen; St. Jude Medical; Teva Pharmaceutical Industries, Ltd.; University of Rochester; and the Parkinson Study Group. He has also received royalties from Cambridge, Elsevier, Hodder Arnold, Lippincott Williams and Wilkins, and Wiley Blackwell. J.L.G. is an employee of Evidence Scientific Solutions, which was contracted to assist in the development of the manuscript. S.P. was an employee of Allergan, Inc. when this study was initiated. He is currently employed at Pfizer, Inc. in Cambridge, Massachusetts.

Conflict of Interests: J.J. has served on the following editorial boards without financial compensation: Medlink: Neurology, Expert Review of Neurotherapeutics, and Neurology in Clinical Practice and has served as an associate editor of The Botulinum Journal, Therapeutic Advances in Neurological Disorders, Neurotherapeutics, Tremor and Other Hyperkinetic Movements, Journal of Parkinson's Disease, and UpToDate.

Figures

Figure 1. Diagram of literature sorting to identify articles that fit the search criteria.