neurologic disorders
Tremor
Pathophysiology of Tremor
Various lesions in the brain stem, extrapyramidal system, or cerebellum can cause tremors. Neural dysfunction or lesions that cause tremor may result from injury, ischemia, metabolic abnormalities, or a neurodegenerative disorder. Sometimes tremor is a familial condition (eg, essential tremor). Tremor is classified primarily based on when it occurs: Resting tremorsare visible at rest and occur when a body part is completely supported against gravity. Resting tremors are minimal or absent during activity. They occur at a frequency of 3 to 6 cycles/seconds (hertz [Hz]). Action tremorsare maximal when a body part is moved voluntarily. Action tremors may or may not change in severity as a target is reached; they can occur at very different frequencies, but the frequency is always < 13 Hz. Action tremorsinclude kinetic, intention, and postural tremors. Kinetic tremorsappear in the last part of a movement toward a target; amplitude is low. Intention tremorsoccur during voluntary movement toward a target, but amplitude is high and frequency is low during the complete movement, while the tremor worsens as the target is reached (as seen in finger-to-nose testing); they occur at a frequency of 3 to 10 Hz. are maximal when a limb is maintained in a fixed position against gravity (eg, holding the arms stretched out); they occur at a frequency of 5 to 8 Hz. Sometimes they are modified by specific positions or tasks, which may indicate their origin; for example, Dystonias may trigger a tremor (dystonic tremor). Complex tremors can have components of more than one type of tremor. Tremor can also be classified based on whether it is Physiologic (within the range of normal) A primary disorder (essential tremor, Parkinson disease) Secondary to a disorder (eg, stroke) Tremor is usually described based on frequency of oscillations (rapid or slow) and amplitude of movement (fine [low amplitude] or coarse [high amplitude]). 