Epidemiology of primary and secondary dystonia

During the last decade, dystonia has been increasingly recognized. However, the body of work concerning the epidemiology of this condition is not extensive. In the past, barriers to epidemiologic study have included perceptions that dystonia is rare and associated with relatively low morbidity. In addition, the absence of validated diagnostic markers for dystonia has limited the careful classification of subjects with this hyperkinetic movement disorder. A further difficulty has arisen because dystonia is a heterogeneous condition that is classified according to the age of onset (early-and late-onset dystonia), body distribution (focal, segmental, multifocal, generalized, and hemidystonia), and etiology (primary and secondary dystonia) (1). Lastly, the evolution of numerous molecular and clinical subtyping systems has lead to some variation in neurologist attitudes in the recognition and treatment of dystonia (2).