Essential tremor

Definition and epidemiology. Essential tremor is the most common tremor disorder and the most common movement disorder, with prevalence up to 3% in the general population and up to 5% in adults over 60, rising to as high as 21.7% in adults over 95.

Pathophysiology. Tremor arises from dysfunction in networks involving the inferior olive, cerebellum, thalamus, basal ganglia and cortex. The basal ganglia network triggers the onset of tremor while the cerebellar network — predominantly affected in essential tremor — modulates its amplitude.

Clinical presentation. A bilateral action-induced (postural and kinetic) tremor of the upper limbs, which may involve head and voice. It may be asymmetric but is usually not unilateral. An intention tremor and a kinetic tremor of greater amplitude than the postural tremor make ET more likely; rest tremor is not typical and suggests parkinsonism. A family history of tremor is common; ethanol may improve and caffeine and smoking may worsen the tremor.

Differential diagnosis. Parkinsonian tremor (rest tremor with rigidity, bradykinesia, postural instability, hypomimia); dystonic tremor (isolated head tremor, unilateral tremor, abnormal posturing or thumb flexion, torticollis, geste antagoniste, arrhythmic and directional head tremor); cerebellar tremor (intention tremor with dysmetria, scanning speech, truncal ataxia); functional tremor (variability, distractibility, entrainment, suggestibility); drug-induced tremor — caffeine, ethanol, nicotine, beta-agonists, tricyclics, lithium, SSRIs, neuroleptics, valproate, amiodarone, ciclosporin, tacrolimus, metoclopramide; and hyperthyroidism, orthostatic tremor and late-onset Wilson's disease. The spiral test is a useful bedside discriminator — ET spirals have one clear axis, dystonic tremor spirals have multiple or no clear axes.

Investigation. In most elderly patients no further workup is required, as clinical assessment is sufficient. Liver function tests and thyroid studies can at times be helpful; EMG is very beneficial for orthostatic tremor; DaTSCAN is normal in essential tremor and abnormal in parkinsonism; MRI with and without contrast is indicated if cerebellar tremor is suspected. Misdiagnosis is frequent and leads to inadequate therapy.

Treatment. There is no curative therapy, and the indication for symptomatic therapy depends solely on the functional and social impairment the patient experiences. First line: propranolol and primidone, which give a 30–70% reduction in tremor amplitude but frequently have to be discontinued for side effects — bradycardia with propranolol; nausea, dizziness and drowsiness with primidone. Second line: topiramate, gabapentin and benzodiazepines. Surgery — deep brain stimulation of the ventral intermediate (Vim) nucleus of the thalamus, gamma knife surgery or focused ultrasound thalamotomy — gives greater amplitude reduction but is reserved for severe medication-refractory tremor.

Staged bilateral MR-guided focused ultrasound thalamotomy is now approved. The FDA approved staged bilateral MRgFUS thalamotomy for essential tremor, with the second side treated at least nine months after the first; the pivotal open-label trial was published by Kaplitt and colleagues in JAMA Neurology 2024. A 2025 Movement Disorders analysis found efficacy comparable to bilateral DBS, with two target "sweet spots" (dorsal Vim–Vop border and ventral Vim/posterior subthalamic area), while prospective series confirm gait and balance impairment as the principal adverse effects — a significant consideration for falls risk in older patients.