Adult-onset focal dystonias: To lump or split.

The adult-onset focal dystonias are a group of clinically heterogeneous disorders that affect different regions of the body. Although they affect different regions with different clinical manifestations, there is evidence that etiopathogenesis is shared at the anatomical, physiological, and genetic levels. However, there is also evidence that etiopathogenesis varies. This chapter summarizes the evidence for lumping or splitting these apparently different clinical phenotypes. It also includes some potential explanations to explain the similarities and differences.