Definition
Tremor is a symptom that results from the rapid alternation of muscle contraction and relaxation. This determines an involuntary and rhythmic oscillation, of one or more parts of the body, with respect to an axis of equilibrium. This symptom is often evident in the hands, tongue and head.
The movements that characterize the tremor can be fine or coarse, rapid or slow. The oscillations can also be evoked by particular actions or postures; based on the moment in which it appears, the tremor can be at rest or kinetic (it manifests itself in the movement aimed at a definitive purpose). Resting tremor is an early sign of Parkinson's disease (usually begins with the hands). The intentional or kinetic form, however, it is present in multiple sclerosis and in some cerebellum diseases.
The tremor can also be classified as physiological (if it falls within a normal range), as a primary disorder (essential tremor) or as a pathological sign of lesions of the central nervous system (eg stroke).
The benign essential tremor has a family basis and tends to worsen with advancing age; it shows an accentuation of the tremor which mainly affects the upper limbs and the head.
The dysfunction or neurological lesions responsible for the tremor can result from trauma, ischemic insults, tumors, infections and demyelinating pathologies. Other causes include endocrinological, metabolic and toxic alterations, such as hyperthyroidism, hypoglycemia, hepatic and anoxic encephalopathy, heavy metal poisoning, hyperparathyroidism and pheochromocytoma.
The occasional tremor can manifest itself, instead, in conditions of stress, intense physical effort, anxiety, fear, fever, cold, intake of caffeine or alcohol. Furthermore, it can represent the effect of drugs, such as sympathomimetics, antidepressants, phenothiazine, lithium and valproic acid.
The tremor can also be induced by the abrupt withdrawal of nicotine in the habitual smoker or drugs in the addict (withdrawal syndrome).
