This is the most common movement disorder. The tremor of ET must be distinguished from early Parkinson's disease (Table 54-1). The pathophysiology of ET is unknown. Approximately 50% of cases have a positive family history with autosomal dominant inheritance; linkage studies have implicated several loci, and recently a mutation in the fused in sarcoma (FUS) gene, previously implicated in familial ALS, was identified in one ET family. The oligodendrocyte gene LINGO1 has been suggested in association studies, especially in early onset familial cases. Many pts with ET have mild symptoms and require no treatment.

• When activities of daily living such as eating and writing are impaired, therapy with propranolol (20-120 mg/d) or primidone (12.5-750 mg/d) leads to benefit in 50% of pts.
• Surgical therapies targeting the thalamus may be effective in refractory cases.