Paroxysmal non-kinesigenic dyskinesia: pathophysiological investigations

The paroxysmal dyskinesias constitute a heterogeneous group of disorders wh ose pathophysiologies and nosologies are still generally unknown. In a boy with severe, paroxysmal non-kinesigenic dyskinesia (PNKD), an invasive vide o-electrographic study demonstrated that his PNKD did not originate from th e cortex, while a discharge was registered from the caudate nuclei. An (18) FDG PET scan failed to show metabolic anomalies. A (18)FDOPA and a C-11 rac lopride PET scans revealed a marked reduction in the density of presynaptic dopa decarboxylase activity in the striatum, together with an increased de nsity of postsynaptic dopamine D-2 receptors. These findings may suggest a chronic upregulation of postsynaptic dopa receptors, either because of an i ncrease in their numbers or changes in their affinity. it remains unknown i i these are secondary to reduced dopamine synthesis or altered release, or if the changes in striatal dopamine receptor binding are a primary or a com pensatory mechanism.