tremor

Tremor is an involuntary rhythmic oscillation of a body part produced by alternating activity in opposing muscles. It is commonly described by its frequency, amplitude, distribution, and the context in which it occurs. In healthy individuals, a small physiologic tremor can be seen, which may be amplified by fatigue, stress, caffeine, or certain medications.

Tremors are classified by context as rest tremor, which occurs while the muscle is not voluntarily activated, and action tremor, which occurs with posture or movement. Action tremors are further divided into postural tremor (holding a position), kinetic tremor (during movement), and intention tremor (increasing in amplitude toward a target, often indicating cerebellar involvement). Several syndromes are recognized, including physiologic tremor, enhanced physiologic tremor, essential tremor, Parkinsonian tremor, cerebellar tremor, dystonic tremor, and psychogenic (functional) tremor.

Common causes range from benign to disease-related. Physiologic tremor can become prominent with anxiety, fatigue, or stimulants. Pathologic tremors arise from neurological conditions such as essential tremor (typically bilateral, mostly hands and forearms, may involve the head), Parkinsonian tremor (often a resting, pill-rolling tremor with asymmetry), cerebellar tremor (intention-type, related to cerebellar disease), dystonia-related tremor, or psychogenic tremor. Metabolic and drug-induced tremors (e.g., thyroid disorders, lithium or valproate, certain antidepressants) are also recognized contributors.

Diagnosis relies on clinical history and examination, sometimes aided by tremor-rating scales, accelerometry, or electromyography to characterize frequency and amplitude and to distinguish tremor types. Imaging and laboratory tests may be used to identify underlying causes.

Treatment targets the underlying condition and symptom burden. For essential tremor, options include propranolol or primidone, with alternatives such as topiramate or alcohol restriction; advanced cases may benefit from deep brain stimulation or focused therapies. Parkinsonian tremor is managed by dopaminergic therapy, while focal tremors may respond to botulinum toxin injections; physical therapy can help improve function.