Muscle Cramps

Muscle cramps are sudden, involuntary, painful contractions of a muscle or part of a muscle, lasting seconds to minutes, usually in the calf, foot or hand, often at night and relieved by stretching, with the muscle palpably hard and sometimes sore for hours afterwards.

• Very common: about 30 to 60 percent of adults over 60 have nocturnal leg cramps; also common in pregnancy (up to 50 percent, mostly in the second and third trimester), in athletes, and in dialysis patients (up to 90 percent).
• Mechanism involves hyperexcitability of the motor nerve terminals and spinal motor circuits; fatigue and altered reflex inhibition are important in exercise associated cramps.
• Most cramps are idiopathic and benign; secondary cramps indicate an underlying disorder.
• Causes (secondary): electrolyte disorders (low potassium, magnesium, calcium or sodium), dehydration, drugs (diuretics, salbutamol and other beta agonists, statins, calcium channel blockers, lithium, levothyroxine excess, penicillamine, nicotinic acid, raloxifene, laxatives, cimetidine, long acting oestrogen), chronic kidney disease and dialysis, cirrhosis, hypothyroidism, diabetes, peripheral neuropathy, motor neurone disease, radiculopathy, peripheral arterial disease, pregnancy, heavy alcohol use, and heat exposure.

• Sudden painful tightening, typically of the calf, hamstrings, quadriceps, feet or hands; the muscle is visibly contracted and hard; lasts from seconds to up to 10 minutes; recurrent episodes during sleep.
• Persistent soreness for several hours after a severe cramp.
• Distinguish from: restless legs (urge to move legs relieved by movement, evening), nocturnal leg pain in peripheral arterial disease, tetany (carpopedal spasm with hypocalcaemia and positive Chvostek and Trousseau signs), fasciculations, myotonia, stiff person syndrome and neuromyotonia.
• Red flags suggesting a secondary cause: progressive weakness, muscle wasting, fasciculations, dysphagia, dark urine (rhabdomyolysis), sensory loss, jaundice, ascites, limb ischaemia, symptoms of hypothyroidism or hypocalcaemia.
• Medication history is key (including recent changes) as well as alcohol, exercise and dietary history.

• Clinical in typical idiopathic nocturnal or exercise related cramps with normal examination.
• Tests when cramps are frequent, severe, persistent, or atypical: urea, electrolytes, creatinine and eGFR; calcium, magnesium, phosphate; glucose or HbA1c; TSH; liver function; creatine kinase; FBC; vitamin D and parathyroid hormone when calcium is low.
• Peripheral pulses and ankle brachial index if vascular disease is suspected.
• Nerve conduction studies and EMG when weakness, wasting, fasciculations or neuropathy are present.
• Differentials: restless legs syndrome, peripheral arterial disease, neuropathy, radiculopathy, hypocalcaemic tetany, myopathy, rhabdomyolysis, stiff person syndrome, deep vein thrombosis, Baker cyst rupture.

Immediate relief

• Passive stretching: for calf cramps, dorsiflex the foot by pulling the toes towards the knee with the leg straight, or stand and put weight on the affected leg; massage and warmth.

Prevention

• Stretching the calves and hamstrings for 10 minutes before bed (hold each stretch 15 to 30 seconds, 3 repetitions) reduces frequency in older adults.
• Maintain hydration; limit alcohol and caffeine; regular exercise; avoid plantar flexed sleeping posture (keep the bed covers loose), and wear supportive footwear.
• For exercise associated cramps: progressive conditioning, adequate fluids and sodium during prolonged activity, and warm up.

Treat causes

• Review and stop or reduce offending drugs: for diuretic induced cramps, check potassium and magnesium and correct (for example oral magnesium glycerophosphate 4 mmol twice daily or magnesium citrate 300 mg daily; oral potassium replacement according to the measured deficit with monitoring).
• Correct hypocalcaemia, hypothyroidism, and diabetes; manage dialysis (adjust dry weight and ultrafiltration).
• Optimise treatment of neuropathy, radiculopathy, and vascular disease.

Medicines (for frequent, disabling cramps after non-drug measures)

• Magnesium supplementation has little proven benefit in idiopathic cramps, but is reasonable in pregnancy: magnesium citrate 300 mg daily or magnesium lactate/citrate 5 mmol twice daily.
• Quinine sulfate 200 to 300 mg orally at night, for a 4 week course only if cramps are severe and frequent and all other measures failed; stop if no benefit within 4 weeks; avoid in QT prolongation, thrombocytopenia, myasthenia gravis, tinnitus, optic neuritis and G6PD deficiency; risk of thrombocytopenia, haemolytic uraemic syndrome, arrhythmia and drug interactions (digoxin, warfarin, flecainide, macrolides). Check FBC.
• Mexiletine 150 mg orally twice daily, increasing to 200 mg three times daily, for refractory cramps in selected patients, including neuromuscular disorders, with ECG; contraindicated in second or third degree heart block and structural heart disease.
• Baclofen 5 mg orally at night, increasing by 5 mg every 3 to 7 days to 10 to 20 mg (especially for cirrhosis; reduce dose in renal impairment; avoid sudden withdrawal).
• Carbamazepine or phenytoin are rarely used; gabapentin 300 mg at night for neuropathic contributions.
• Avoid routine use of calcium channel blockers, vitamin E and B complex preparations, which have little supporting evidence.

Follow up

• Review at 4 weeks; investigate further and refer if cramps persist with weakness, wasting or abnormal tests.

Special groups

• Pregnancy: stretching, hydration, magnesium citrate 300 mg daily; check calcium and magnesium; avoid quinine (teratogenic risk and fetal thrombocytopenia).
• Cirrhosis: baclofen 5 mg at night increasing slowly; avoid NSAIDs and quinine; correct albumin where low; zinc replacement if deficient.
• Haemodialysis: reduce ultrafiltration rate, adjust dry weight, use higher dialysate sodium, and give carnitine if deficient (levocarnitine 20 mg/kg after dialysis) under specialist supervision.
• Children: stretching and hydration; investigate for electrolyte disturbances, metabolic myopathies, and drugs.