Patients with
Parkinson's disease (PD) often complain of unsteadiness. This can occur as the result of various neurological dysfunctions, including changes in postural adjustments, loss of postural reflexes, axial akinesia and rigidity, freezing and/or
postural hypotension. In some cases these symptoms remain unexplained, and rare cases of unsteadiness have been attributed to
tremor on standing. To delineate this condition, we investigated 11 consecutive PD patients with unexplained unsteadiness because of
tremor on standing, seen in our department over a 6-year period. All the patients had detailed clinical and electrophysiological investigations based on surface polygraphic electromyographic recordings. Four patients had fast orthostatic
tremor (13-18 Hz), one had intermediate orthostatic
tremor (8-9 Hz), and three had slow orthostatic
tremor (4-6 Hz). The remaining 3 patients had orthostatic
myoclonus, a condition that has not previously been reported in PD. Patients with fast
tremor improved on
clonazepam. Patients with slow
tremor and
myoclonus improved on
levodopa and sometimes benefited further when
clonazepam was added. These observations show the usefulness of neurophysiological investigations for diagnosing and treating unexplained unsteadiness in
Parkinson's disease.