Dystonia musculorum deformans: a 'critical phenomenon' model involving nigral dopaminergic and caudate pathways.

In physical systems, a 'critical phenomenon' is a macroscopic occurrence which arises from a change in the relative magnitudes of two or more physical influences whose action is expressed purely in microscopic terms. This concept is potentially valuable in describing the clinical symptomatology of dystonia musculorum deformans (DMD) and other movement disorders. The lateral inhibitory network of Spiny I caudate cells and the profuse neostriatal projection of dopaminergic neurons from the substantia nigra are proposed as anatomic substrates for two short-range neostriatal influences whose interaction contributes to the onset and progression of global dystonic spasm in DMD. Such spasm may be explainable as a critical phenomenon, suggesting new directions for research into the etiology and treatment of this disorder.