The 'essentials' of essential palatal tremor: a reappraisal of the nosology.

Essential palatal tremor (EPT) is an uncommon disorder, distinct from symptomatic palatal tremor (SPT), but characterized by superficially similar rhythmic movements of the soft palate. While the pathophysiology of SPT has been relatively well defined, this is not the case in EPT. Based on an analysis of 103 published cases, we reviewed EPT in the context of other movement disorders with similar features and outline possible pathophysiological mechanisms. Phenomenologically it remains best classified as a tremor. Four major causes, including a central generator, peripheral/mechanical, voluntary/special skill and psychogenic, appear to account for the majority of cases of EPT, although there is considerable overlap in the pathogenic mechanisms underlying these categories. Among the cases reviewed, a large proportion fit into the latter two categories, although there are others where multiple mechanisms are likely at play. Based on our reappraisal, we suggest a change in designation to 'isolated palatal tremor', with primary and secondary subtypes. This retains the distinction from SPT and emphasizes the non-uniform, heterogeneous nature of the disorder.