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Author: Michael H. Brook

A brief review.

Inspection of the limbs may reveal changes of muscle bulk: wasting of muscles, which is more common in the denervating diseases, or enlargement of muscles, as is seen in some of the dystrophies. Abnormal twitching of the muscles may be noted at rest. This may be either fasciculation or myokymia.

A fasciculation is a brief involuntary contraction of a small area of the muscle, not sufficient to move the joint but noticeable to the naked eye. Profuse fasciculations may accompany amyotrophic lateral sclerosis and some other denervating disorders. Often, they are present in all limbs and are easy to spot. More difficult is knowing how to interpret the isolated fasciculation.

Fasciculations by themselves may have little significance. Most of us experience these small twitches from time to time. They are exacerbated by fatigue, either physical or mental, and by caffeine or the consumption of other stimulants. Even in the healthy individual, they may become quite widespread and persistent for a period of time.

In the context of other signs of neuromuscular involvement, fasciculations do imply a denervating process, particularly anterior horn cell disease. In the absence of any other abnormalities, occasional fasciculations may have no significance.

Myokymia may be very hard to differentiate from fasciculations, and the only reliable way to do it is with the EMG. Myokymic twitches are longer in duration and are often more frequent than fasciculations, giving the muscle surface a roiling, rippling aspect like the wind blowing across a field of grain. Myokymia is an irritative phenomenon in the nerve, producing trains of tetanic activity. Although it may be seen in diabetes, in hypocalcemia, or during recovery from nerve entrapment or a pressure palsy, it may also arise spontaneously.

Michael H. Brook, 1999
Section Last Modified:
8/22/2010 11:12 PT