Primary orthostatic tremor and unsteadiness

✍ Scribed by Pierre Jedynak; Yves Agid

• Publisher: John Wiley and Sons
• Year: 2004
• Tongue: English
• Weight: 75 KB
• Volume: 19
• Category: Article
• ISSN: 0885-3185
• DOI: 10.1002/mds.20192

✦ Synopsis

We read with interest the article by Sharott and colleagues 1 in which they suggest that "the core abnormality in primary orthostatic tremor may be an exaggerated sense of unsteadiness when standing still." This original hypothesis is based on the proposition that "a physiological system is involved in organizing postural responses under circumstances of imbalance. . .characterized by a highly synchronized output at approximately 16 Hz". 1 This idea, although interesting, is difficult to accept. The 16-Hz tremor is independent of the postural response of patients, because it disappears when the subject leans against a wall or when significant pressure is applied to the soles of the feet. 2 As shown in a patient with orthostatic tremor (Fig. 1), 16-Hz rhythmic activities alternate between the left and right quadriceps when the patient walks in place. The tremor is only observed in the limb on which weight is placed. It disappears when weight is shifted to the other leg. This finding indicates that orthostatic tremor is caused by pressure.

For primary orthostatic tremor to result from unsteadiness, the instability needs to have a cause. To our knowledge, such instability does not result from additional frontal, cerebellar, proprioceptive, or vestibular dysfunctions. Furthermore, other causes of postural instability are not accompanied by 16-Hz tremors. It is, indeed, difficult to believe that postural instability results solely from the existence of a 16-Hz tremor. An alternative hypothesis is that orthostatic tremor is triggered by the weight of the body when standing still and that the slight imbalance which ensues aggravates the tremor.