Tremor disorder (shaking)

Tremor is one of the most common symptoms in neurology and the most common movement disorder. Tremor describes an involuntary, oscillatory movement of one or more parts of the body, which usually occurs in the hands but can also affect the head, voice, or legs, among other things. Depending on the conditions under which the tremor occurs, a distinction is made between a resting tremor, which occurs when the body part is relaxed, and an action tremor. Action tremor is further divided into postural tremor, which occurs when holding against gravity, movement tremor, which occurs during movement, and intention tremor, which occurs during purposeful movements and increases as the target is approached. A tremor can occur as an independent clinical picture (primary tremor disorders) or as a symptom of another disease (secondary tremor disorders, e.g., in the context of another neurological disease such as Parkinson's disease or multiple sclerosis, as well as in internal diseases such as hyperthyroidism).

Even in healthy people, a slight, usually barely visible tremor can be observed when holding out the arms or legs. This tremor is not indicative of any disease and is referred to as physiological tremor.  Increased physiological tremor, on the other hand, is usually visible and can be situational or permanently disruptive. This tremor can be triggered by tension, anxiety, caffeine, or fatigue. Other causes can include adverse drug reactions or metabolic disorders.

The most common form of primary tremor disorders is essential tremor, which by definition occurs in both hands but can also affect other parts of the body as the disease progresses. Essential tremor has a familial clustering, meaning that other family members are usually also affected.

Orthostatic tremor causes high-frequency vibrations in the leg muscles when standing, which improve when walking or sitting. Orthostatic tremor leads to unsteadiness when standing. Externally, tremors are often not noticeable, but the typical high frequency of the tremor (14-18 Hz) can be measured using surface electromyography in tremor analysis.

Cerebellar tremor occurs in the context of various diseases of the cerebellum, such as multiple sclerosis or neurodegenerative diseases such as hereditary ataxia. It often manifests as intention tremor of the extremities, less commonly of the trunk.