Tremor syndromes: A review

Among the involuntary movement disorders, tremor is a common phenomenology seen in clinical practice. The important factors that need to be determined while assessing a patient with tremor include the phenomenology of tremor, presence or absence of other neurologic signs, and the effect of medications or alcohol. Tremor can broadly be classified based on the circumstances under which it occurs, i.e., rest or action. The basal ganglia-cerebello-thalamic and dentate-olivary circuits are involved in the generation of tremor. Experimental data have suggested the olivocerebellar system as the site of the central oscillator in essential tremor. Generation of tremor in Parkinson's disease results from loss of dopaminergic neurons of the retrorubral area causing dysfunction of the globus pallidus, which finally leads to abnormal firing pattern of the ventrolateral posterior neurons of the thalamus. Involvement of the cerebello-thalamic pathways leads to orthostatic tremor. Palatal tremor is thought to be generated by the cells of the inferior olive. Holmes tremor usually results from the disruption of the dentate-rubro-thalamic circuit and also the nigro-striatal circuit. Multiple drugs can cause tremors. Demyelinating neuropathies are associated with tremors. Involvement of the deep cerebellar nuclei, cerebellar outflow tracts and the cerebrocerebellar loops has been postulated in the cerebellar tremor production. Electrophysiological methods are valuable in characterizing tremors. In addition to the pharmacological therapy including botulinum toxin therapy, surgical therapies in form of DBS or lesional surgeries are beneficial in reducing the symptoms.