Muscle Cramps and Stiffness
Stiffness: continuous muscle contraction at rest.
Cramps (spasms): transient, painful, involuntary contraction of muscle or group of muscles; lasts seconds to minutes. Causes listed in Table 130.1.
Ordinary Muscle Cramps
Provoked by trivial movement or by contracting already shortened muscle. Predisposing factors: during or after vigorous exercise, pregnancy, hypothyroidism, uremia, profuse sweating or diarrhea, hemodialysis, lower motor neuron disorders (especially anterior horn cell diseases); often occur in bed at night or on waking in the morning.
EMG: brief, periodic bursts of motor unit potentials discharging at 200 to 300 Hz. Activity arises within anterior horn cell, distally along motor nerve, or both.
Treatment: stretching affected muscle usually terminates cramp; e.g., walking for gastrocnemius cramp. Nocturnal leg cramps prevented by bedtime dose of quinine, phenytoin, carbamazepine, or diazepam. Frequent daytime cramps: carbamazepine or phenytoin.
Benign fasciculation with cramps (Denny-Brown, Foley syndrome): inordinately frequent cramps, often with fasciculations. No weakness or upper motor neuron signs; almost never transforms to motor neuron disease.
Contracture: painful shortening of muscle with no electrical activity on EMG. Seen in McArdle disease (phosphorylase deficiency); attributed to depletion of adenosine triphosphate (ATP).
Table 130.1 Motor Unit Disorders Causing Cramps and Stiffness | ||||||||||||||||||||||||||||||||||||||||||||||||||||
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