Re: Involentary Muscle Twitches - WHAT IS THIS!!!

July 29, 2000

http://nuaserver1.swmed.edu/pearls/pearl9/pearl9.htm

No. 9

Fasciculations

Do you ever experience involuntary muscle twitching, especially around the

eyes (orbicularis oculi) or in the intrinsic muscles of the hands?

Fasciculations, which most people experience occasionally, are visible as

rapid, small amplitude twitches of a small portion of a muscle and usually

not producing movement at a joint. However, fasciculations can indicate

serious neurological disease. When should the physician be concerned if the

patient complains of muscle twitching?

Fasciculations are spontaneous contractions of one or several motor units. A

motor unit is a neuron and all the muscle fibers it innervates. The number of

muscle fibers in a motor unit varies with the muscle. Small, precise muscles,

such the extraocular muscles, contain only a few muscle fibers in each motor

unit, allowing finer control over the movements; larger muscles, such as the

quadriceps, contain hundreds of muscle fibers in each motor unit.

Electrically, fasciculations are large compound action potentials that can be

detected electrically even if they produce no visible movement. One of the

functions of electromyography in patients with apparent isolated muscle

twitches is to determine whether there are subclinical fasciculations at

other sites, indicating more widespread disease.

When accompanied by weakness, atrophy, and reduced stretch reflexes,

fasciculations usually indicate disease of the cell body of the motor unit.

Disorders of nerve roots or peripheral nerve axons may also produce

fasciculations, but, for reasons that are unclear, disorders of the nerve

fiber produce fasciculations less often than anterior horn cell diseases. The

most common (and severe) neurological condition associated with widespread

fasciculations is amyotrophic lateral sclerosis (ALS, or Lou Gehrig's

disease). This is a disease of unknown etiology in which the pathology is in

the anterior horn cells and the corticospinal tracts.

Benign fasciculations are usually precipitated by fatigue or stress. When a

motor unit is overworked, it may start to twitch. A new exercise regimen can

produce fasciculations in the overworked muscle for hours. Students sometimes

note that the muscles in their hands or around their eyes start to twitch the

night before an important exam. Fasciculations can also be precipitated or

exacerbated by anticholinesterase medications, caffeine, and smoking.

Several clues help the physician distinguish benign fasciculations from the

ominous fasciculations of motor neuron disease. In the patient with motor

neuron disease, the muscle twitch often occurs once or twice in one muscle,

then in another muscle, and then in different spots in the limb. These

" migratory " fasciculations are sometimes difficult to find, because they move

from place to place before the examiner can observe them. Benign

fasciculations tend to remain in the same area. Also, benign fasciculations

are almost always first noticed by the patient. However, patients with motor

neuron disease usually come to the doctor complaining about weakness in an

arm or leg. During physical examination, the doctor notes that there are

muscle twitches in the limbs or tongue. When questioned about the twitches,

the patient indicates that he or she has not noticed them before, even if

they are extremely prominent on examination. Migratory fasciculations, of

which the patient is unaware, are much more worrisome for a malignant process

although they also may occasionally be benign. Fasciculations are common and

usually innocuous. However, even when unaccompanied by neurological disease,

they mimic one of the symptoms experienced by people with ALS, one of the

most serious neurological diseases.

W. , Assistant Professor, Department of Neurology

July 29, 2000