Paroxysmal non-kinesigenic dyskinesia: pathophysiological investigations

The paroxysmal dyskinesias constitute a heterogeneous group of disorders whose pathophysiologies and nosologies are still generally unknown. In a boy with severe, paroxysmal non-kinesigenic dyskinesia (PNKD), an invasive video-electrographic study demonstrated that his PNKD did not originate from the cortex, while a discharge was registered from the caudate nuclei. An 18FDG PET scan failed to show metabolic anomalies. A 18FDOPA and a 11C raclopride PET scans revealed a marked reduction in the density of presynaptic dopa decarboxylase activity in the striatum, together with an increased density of postsynaptic dopamine D2 receptors. These findings may suggest a chronic upregulation of postsynaptic dopa receptors, either because of an increase in their numbers or changes in their affinity. It remains unknown if these are secondary to reduced dopamine synthesis or altered release, or if the changes in striatal dopamine receptor binding are a primary or a compensatory mechanism.