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Primary Orthostatic Tremor and Orthostatic Myoclonus

Timothy C. Hain, MD Last updated September 21, 2010

Primary orthostatic tremor (OT) consists of rhythmical muscle contractions causing discomfort or unsteadiness while standing. It was first described by Heilman in 1984. The tremor is typically 12 to 18 Hz, with partial or complete cessation while walking or sitting. Persons with orthostatic tremor feel very unsteady but rarely fall (Fung et al, 2001)

It is presently controversial whether OT is a variant of essential tremor, a consequence of unsteadiness (Sharott et al, 2003) or a diagnostic entity in its own right (Gabellini, 1990). Findings similar to OT can be induced in normal persons made unsteady through vestibular stimulation(Sharott et al, 2003) Occasionally OT is found in association with essential tremor, and it can follow head injury (Sinitate et al, 1993)

Orthostatic myoclonus (OM) is an nearly, or perhaps completely identical disorder recently reported by by authors at the Mayo clinic in 2007 (Glass et al, 2007). Similar to OT, this condition is typlified by muscle contractions associated with upright stance, and diagnosed using surface EMG. Exactly similar to OT, there are bursts of muscle contraction. In OM, the bursts are irregular, while in OT, they are regular. Again identical to OT, the treatment proposed is klonapin. In the author's opinion, OM and OT are the same condition.

Diagnosis

Diagnosis is usually obtained based on clinical evaluation combined with surface electromyogram (EMG). Surface EMG contains a high-frequency component -- 16 to 18 Hz. Misdiagnosis is common and many patients are initially thought to have a non-organic (psychogenic) balance disorder. Frequency domain analysis of surface EMG or sway traces can diagnose this condition (Yarrow et al, 2001). As a similar tremor can be induced in normal persons via vestibular stimulation (Sharott et al, 2003), conditions that cause imbalance should be considered in addition.

Treatment

According to Pradalier and associates(2002), clonzepam is the preferred treatment for orthostatic tremor. This is also the medication recommended by Glass and associates for orthostatic myoclonus. Other drugs that may be effective include primidone(Mysoline) as well as it's relative phenobarbital (Cabrera, 1991) and gabapentin (Neurontin) (Evidente et al, 1998; Onofrj et al, 1998). Dopamine agonists such as Pramipexole (mirapex) and Levodopa may be worth trying (Finkel, 2000; Wills et al, 1999). Although beta-blockers are often useful in essential tremor, they have been reported not to be effective in OT (Wee, 1986)

References

Copyright October 6, 2013 , Timothy C. Hain, M.D. All rights reserved. Last saved on October 6, 2013