Special concerns in defining, studying, and treating dystonia in children.

Dystonia is movement disorder with many diverse underlying etiologies. Some of those etiologies manifest at specific stages of development or at specific ages. Others may present early in life and evolve as the individual develops. The appearance of symptoms during a time of nervous system development poses special challenges to the neurologist. Normal functions change appearance, dysfunction may manifest in an age-dependent manner, and age-dependent differences in beneficial and toxic effects of treatments all introduce complexities to the process of diagnosis, functional assessment, and therapeutics. Consideration of these developmental differences is essential in assuring a universal definition of dystonia, and for developing valid and reliable assessment tools that can be compared across the lifespan, and more effective therapeutics. © 2013 Movement Disorder Society.