A large number of patients with Parkinson's disease were reported to have abnormal visual-evoked potentials (VEPs) and spatiotemporal contrast sensitivity (STCS) suggesting dopaminergic deficiency in the visual pathway, probably the retina. Until now, VEPs and STCS have not been studied in multiple system atrophy (MSA). We investigated 12 patients with idiopathic Parkinson's disease (IPD) and 12 patients with MSA. The age medians were 64.5 years for IPD and 63.5 years for MSA. None of the patients showed any ocular disease that could interfere with the results. Checkboard VEPs and STCS measurements to horizontal sinusoidal gratings were evaluated. Statistical analysis was performed, including Student's t test and two- or three-way analysis of variance. A significant interocular difference in spatial contrast sensitivity was observed in IPD, which was not present in MSA. VEPs were not delayed in MSA, whereas latency of the major component and the second negative deflection were increased in IPD. VEPs and STCS measurements might provide useful help for distinguishing IPD from MSA.
Action tremor has been described in cerebellar, task-specific, dystonic, or Holmes tremor. We report 2 patients who developed unilateral kinetic or isometric action tremor of the upper extremity, following cervical spondylotic myelopathy and capsular ischemic stroke. Slight motor weakness and spasticity with exaggerated tendon jerks and passive stretch-induced clonus were present on the same limb. The central motor pathways lesions might have been responsible for a hyperexcitability of the stretch-reflex arc and an enhancement of the coactivation of skeletal muscles through a loss of the descending or segmental control of the spinal reflexes. The unusual topography of the symptoms, their occurrence during motion, and the similar frequency of the passive clonus and the action tremor, led us to hypothesize that both patients had prolonged action-induced clonus, mimicking action tremor. Lesions of the central motor pathways lesions might be responsible for action tremor under certain conditions.
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