trembling

Trembling, or tremor, is an involuntary, rhythmic oscillation of a body part produced by alternating or synchronous contraction of opposing muscle groups. It is often visible in the hands but can involve the head, voice, legs, or trunk. Tremor is different from spasticity, clonus, or fasciculations, and it may occur at rest, during posture, or with movement.

Tremors are commonly classified by their context and origin. Physiological tremor is a normal, usually subtle tremor that can be amplified by fatigue, caffeine, or cold. Pathological tremors are caused by neurological disease or other medical conditions and are further categorized as rest tremor (most evident when the limb is at rest), postural tremor (maintained against gravity), or intention/kinetic tremor (increasing with purposeful movement, often toward a target). Common examples include essential tremor, Parkinsonian tremor, dystonic tremor, cerebellar tremor, and tremor due to thyroid disease or drug effects.

Causes include aging-related changes in the nervous system, neurodegenerative disorders, metabolic disorders, medications, anxiety, and withdrawal from substances. Mechanistically, tremor results from abnormal signaling in brain circuits that control movement, especially the basal ganglia, cerebellum, and thalamus, with contributions from peripheral muscle and autonomic factors.

Diagnosis is based on history and examination, focusing on tremor type, distribution, and triggers. Tests may include blood work for thyroid function and metabolic abnormalities, drug history, and sometimes neuroimaging or electrophysiological studies to clarify the source.

Management targets the underlying cause and symptom relief. Treatments for significant tremor may include medications (beta-blockers, anticonvulsants, or dopaminergic therapy depending on cause), physical or occupational therapy, and, in severe cases, surgical interventions such as deep brain stimulation. Many tremors are controllable or stable with appropriate care, but some progressive conditions warrant ongoing medical management.