Tremor

Tremor is an involuntary, rhythmic, oscillating movement of one or more body parts produced by alternating or synchronous contractions of opposing muscle groups. It is the most common movement disorder and can occur as the primary manifestation of a neurological condition — as in essential tremor and Parkinson's disease — or as a secondary feature of many other diseases, medications, and metabolic states. Characterizing tremor accurately is essential for diagnosis: the clinical distinction between a rest tremor (present when the limb is fully supported and relaxed) and an action tremor (occurring during voluntary movement or while maintaining a posture against gravity) significantly narrows the differential diagnosis and guides appropriate investigation and treatment.

Tremor arises from abnormal neural oscillation at one or more levels of the motor system — from the cerebral cortex and thalamus through the basal ganglia and cerebellum to the spinal cord and peripheral nerve. Common causes include:

• Essential tremor — the most common cause; an action tremor predominantly affecting the hands and arms, often with a positive family history and a characteristic response to alcohol and propranolol.
  
  
• Parkinson's disease — characterized by a rest tremor of the hand, often starting unilaterally, accompanied by bradykinesia, rigidity, and gait changes; the combination of these features distinguishes it from essential tremor.
  
  
• Dystonic tremor — an irregular tremor superimposed on dystonic posturing; may affect the head, neck, or hands in cervical dystonia or focal hand dystonia.
  
  
• Cerebellar tremor — an intention tremor (tremor that worsens as the limb approaches its target) reflecting cerebellar pathway dysfunction; may occur with cerebellar tumors, multiple sclerosis, or cerebellar stroke.
  
  
• Physiological and enhanced physiological tremor — the fine tremor of the hands present in all people under stress, fatigue, caffeine, or certain medications (bronchodilators, lithium, valproate, thyroid hormone); generally fine, fast, and symmetric.
  
  
• Drug-induced tremor — dopamine-blocking medications, lithium, valproate, and stimulants are common culprits; medication review is essential in all new tremor presentations.

Not all tremor requires immediate medical attention, but evaluation by a neurologist or movement disorder specialist is recommended in the following circumstances:

• New-onset tremor that interferes with daily activities — such as eating, writing, or using a phone — regardless of the presumed cause.
  
  
• Tremor combined with other neurological symptoms — such as slowness of movement, balance problems, rigidity, speech change, or cognitive difficulties — which may suggest Parkinson's disease or another movement disorder requiring specific treatment.
  
  
• Tremor at rest — rest tremor is unusual in essential tremor and warrants evaluation to exclude Parkinson's disease or other basal ganglia disorders.
  
  
• Tremor with a progressive course — worsening over weeks to months deserves specialist assessment and, in some cases, neuroimaging.
  
  
• Tremor in a person with known brain or cerebellar pathology — which may indicate disease progression or a treatment effect