Orthostatic myoclonus: a contributor to gait decline in selected elderly.

BACKGROUND

We encountered 15 patients with a newly recognized clinical phenomenon that we term orthostatic myoclonus. We conducted a retrospective chart review to better understand the clinical context and importance of this phenomenon.

OBJECTIVE

To describe the clinical picture of orthostatic myoclonus.

METHODS

The Mayo Clinic Rochester Movement Disorders Laboratory database was searched for all patients diagnosed electrophysiologically with orthostatic myoclonus (2002 through 2006). Medical records and laboratory data of all patients were retrospectively reviewed.

RESULTS

Fifteen patients with orthostatic myoclonus were identified, all seniors (64 to 81 years). Seven of the patients had a CNS degenerative disorder and two had a systemic illness known to be associated with myoclonus. In the remaining six patients no known CNS disorder contributed to the phenomenon. The onset of orthostatic myoclonus was accompanied by complaints of leg jerking or observed leg jerking in 13 of 15 patients during upright posture. An insidious deterioration of gait that was often described as "apraxia" or "gait initiation difficulty" accompanied the myoclonus in 13 of 15 patients. Clinicians frequently suspected normal pressure hydrocephalus or orthostatic tremor syndrome. Surface EMG studies revealed short duration myoclonic bursts that occurred predominately with the assumption of an upright posture. Some patients improved on clonazepam.

CONCLUSIONS

Orthostatic myoclonus is a unique clinical and physiologic phenomenon that accompanies a slowly progressive and eventually disabling gait disorder in the elderly. This phenomenon often arises in the company of more widespread CNS disease.