[Primary orthostatic tremor: slow harmonic component as responsible of inestability]

Orthostatic tremor (OT) is clinically defined as a tremor of the lower limbs and trunk on walking. It bears a significant functional impairement. Although the term orthostatic tremor was first used by Heilman in 1984, Pazzaglia et al had previously described some cases in 1970. Despite the fact that the pathophysiology of this entity is not fully known, the presence of a central oscillator is generally accepted as being responsible. A high frecuency tremor, between 13 and 18 Hz, constitutes an almost patognomonic finding, and treatment with clonazepam usually improves the symptoms.

We present a patient who described his symptoms as "cramps" in lower limbs and trunk on standing up, which were relieved on walking or resting.

This clinical presentation together with a neurophysiological recording of the tremor showing an activity of lower frequency (8 Hz) combined with the usual higher frequency (16 Hz) and above all the clear amelioration of symptoms when treated with gabapentin, i.e. resolution of the low frequency tremor without changes in the 16 Hz tremor, were the peculiar features of this case which merits discussion.

The slow component of the orthostatic tremor is crucial in this case. The improvement with gabapentin is explained by the disappearance of this slow c