Muscle Cramps

Muscle cramps are very common and 'cramp' is usually taken to mean "a spasmodic, painful, involuntary contraction of skeletal muscle"¹, and there are many causes. This transient, involuntary episode of pain is usually brief (<10 minutes). The lower limbs are almost invariably involved. However, no single accepted definition of muscle cramp exists and many classifications of muscular cramps have been attempted. Cramps can be grouped according to their underlying aetiology:

• Paraphysiological cramps
• Symptomatic cramps
• Idiopathic cramps

When patients complain of cramps it is important to clarify exactly what they mean as the term is frequently used to describe any muscular 'tightness'.

Groups at increased risk:

• The elderly - prevalence increases with age: about a third of people over 60 and half of those over 80 complain of cramps.² The problem is often distressing, impacting on sleep, and has an adverse effect on quality of life.
• Pregnant women - 45% in one survey had suffered from leg cramps during pregnancy, particularly during the third trimester.³
• Children over 12 years, peaking in incidence between 16-18 years.⁴
• Those with metabolic disorders; for example, 50% of patients with uraemia and 20-50% of those with hypothyroidism complain of muscle cramps.⁵
• Athletes and individuals working under hot conditions, e.g. firemen.

Find out what the patient means by cramps:

• Where do they occur? When do they occur? How often?
• How long do they last?
• Is there any other relevant medical history such as thyroid disease or CVD?
• Are drugs taken? For example, diuretics, salbutamol, nifedipine.
• Ask about alcohol consumption.
• Ask about sport.

Most often cramps involve the calf or thigh muscles and small muscles of the foot. Of these, the most commonly affected is the calf and it tends to be unilateral.

Cramps occur at rest and usually at night. The most likely explanation is that leg cramps occur when a muscle that is already in a shortened position is involuntarily stimulated. This commonly happens at night where the plantar flexed foot places the calf and ventral foot muscles in the most shortened and vulnerable position. The cramp may last seconds or minutes but post-cramp tenderness may last up to 24 hours.

• During an attack the affected muscle or group is hard and tender.
• Between attacks examination is unlikely to be rewarding.
• The muscle may be tender for up to 24 hours after the last attack.
• In the elderly, or where peripheral vascular disease is suspected, check for peripheral pulses and capillary refill.
• Look for signs of neurological disease, e.g. muscle wasting and fasciculations, altered reflexes, sensory or power loss.

• Paraphysiological cramps occur in healthy people in response to a physiological stimulus. They are very common and may occur during sport or in unaccustomed exercise. They are especially likely to occur during endurance sports.
• They are thought to result from hydro-electrolyte imbalance following repeated and chronic use of the same muscle group, producing increased excitation of the neuromuscular nerve endings.⁶
• It is thought that low levels of magnesium and other electrolytes may also play a part.
• They are also very common in pregnancy. The aetiology in pregnancy is unknown: pressure on nerves and blood vessels, circulatory changes and low levels of calcium and magnesium have all been suggested.
• They may also occur in healthy individuals as a result of a sustained posture over a prolonged period of time.

Cramps may also occur in association with metabolic disturbance, including:

• Hyponatraemia
• Hypokalaemia and hyperkalaemia
• Hypocalcaemia
• Hypomagnesaemia
• Hypoglycaemia

One or more of these may be the underlying aetiology in many of the causes listed below. Blood tests measure the extracellular environment but do not reflect the intracellular fluid which is probably more important.

• Arterial insufficiency
• Acute or chronic diarrhoea
• Excessive heat and sweating causing Na⁺ depletion
• Hypothyroidism (associated with weakness, enlarged muscles and painful muscle spasms)
• Hyperthyroidism (associated with myopathy)
• Lead poisoning
• Sarcoidosis
• Hyperparathyroidism (hypercalcaemia)
• Heavy alcohol ingestion and cirrhosis
• Hyperventilation-induced respiratory alkalosis
• Haemodialysis
• Parenteral nutrition
• Lower motor neurone disorders including amyotrophic lateral sclerosis, polyneuropathies, recovered poliomyelitis, peripheral nerve injury and nerve root compression

This is a diagnosis of exclusion but represents the majority of sufferers. Familial forms exist which appear to have an autosomal dominant mode of transmission.⁸ This group also contains conditions such as idiopathic nocturnal cramps and fasciculation-cramp syndrome.

Includes:

• Restless legs (Ekbom's syndrome)
• Intermittent claudication and ischaemic rest pain
• Muscle injury or strain
• Hypnagogic muscle jerking (when falling asleep)
• Lumbar nerve root entrapment
• Ruptured Baker's cyst
• Deep vein thrombosis or thrombophlebitis
• Peripheral neuropathy
• Occupational cramps, e.g. writer's cramp or musician's cramp (focal dystonias, usually affecting the upper limb)
• Causes of generalised muscle pain, e.g. polymyositis, toxoplasmosis, alcohol-related myopathy, Guillain–Barré syndrome, polymyalgia rheumatica, Parkinsonism, fibromyalgia

Usually no investigation is indicated. They may be performed if an underlying cause is suspected.

Potential investigations include:

• U & Es
• Liver function tests
• Thyroid function tests
• Serum calcium or magnesium
• Creatine kinase
• Lead levels

General

• In most cases the aetiology is benign and the patient needs to be reassured of this whilst steps are taken to help alleviate the problem. Exclude known causes of muscle cramps without excessive and unnecessary investigation.
  
  
• Management depends upon the cause of the problem. Review drugs. Address any correctable problems, e.g. use of diuretics and electrolyte imbalance.
• The severity of symptoms and their impact on sleep, mood, and quality of life will determine whether treatment is required. Asking patients to keep a sleep and cramp diary may be helpful to assess progress.⁹
• The evidence base for management of this common but usually benign condition is not strong.

Non-drug

Advise:

• Passive stretching and massage of the affected muscle will help ease the pain of an acute attack - e.g. for calf cramping, straighten the leg with dorsiflexion of the ankle or heel walk until the acute pain resolves.
• Regular stretching of the calf muscles throughout the day may help to prevent acute attacks. Some people recommend stretching 3 times daily whilst others advocate stretching before going to bed.
• Using a pillow to raise the feet through the night, or raising the foot of the bed may help to prevent attacks in some people.

Drugs

• Quinine sulphate has been the most frequently used drug in the UK for the treatment of leg cramps in non-pregnant individuals who have not responded to conservative measures. However, it is not generally recommended due to the poor benefit-to-risk ratio. The FDA in America has banned the use of quinine for this indication. Quinine has an extensive side-effect profile, including thrombocytopenia as an important but rare complication. Evidence for its long-term efficacy is lacking.
  However, a n=1 trial approach¹³ may be used where self-care measures fail and leg cramps are frequent and affecting the person's quality of life:⁵
  • Prescribe 200–300 mg nocte for 4–6 weeks.
  • Monitor using a sleep and cramp diary.
  • If helpful, continue treatment for 3 months, then stop to reassess ongoing need.
  • If ongoing treatment is required, regular medication reviews should occur every 3–6 months.
  Quinine can frequently be stopped without a recurrence of troublesome symptoms.¹⁴
• Potential drug alternatives to quinine include verapamil and gabapentin in the general population and vitamin E or L-carnitine in the dialysis population.^15,16
• Avoid quinine in pregnancy and concentrate on non-drug measures where possible. Calcium lactate is ineffective but magnesium supplements may help relieve the symptoms in pregnant women who have not responded to conservative measures.¹⁷
• Traditionally, sodium chloride has been thought to be beneficial, although the trial evidence is old and the potential of added salt to cause hypertension may cause concern.