Investigations
1st investigations to order
clinical diagnosis
Test
Most people presenting with cramps have idiopathic cramps, which are usually diagnosed following clinical exam. Further investigations are only required if the cramp has atypical features or other associated conditions are suspected.
Result
commonly diagnosed on history and clinical exam
Investigations to consider
serum or urine hCG
Test
Performed to verify or rule out pregnancy as a possible association with muscle cramps.
Result
elevated in pregnancy
fasting serum metabolic panel
Test
Possible derangements include elevated or low potassium, sodium, magnesium, or calcium. Check ionised calcium if serum albumin is low.
Hyperphosphataemia in patients with end-stage renal disease enhances cramps, particularly during dialysis sessions in patients undergoing haemodialysis.
Elevated fasting blood sugar seen in diabetes.
Result
may show electrolyte abnormality or diabetes
thyroid-stimulating hormone (TSH)
Test
Indicated to verify hypo- or hyperthyroidism. Further thyroid function tests may be warranted.
Elevated TSH is consistent with primary hypothyroidism.
Suppressed TSH is consistent with hyperthyroidism.
Both are occasionally associated with cramping illness.
Result
abnormal in thyroid dysfunction
HbA1c
Test
May be suggestive but not confirmatory for hypoglycemia.
Result
lower than expected value in relation to observed control via fingerstick blood glucose may suggest hypoglycaemia in diabetes
serum liver function tests
Test
Performed to assess degree of hepatic impairment.
Cramps are associated with presence of advanced cirrhosis (e.g., Child-Pugh class C liver disease).
Result
elevated liver enzymes in hepatic disease; may be normal in advanced cirrhosis
prothrombin time (PT) and INR
Test
Performed in people with suspected or known liver disease and cramps.
Prolonged PT and elevated INR are associated with severe cirrhotic liver disease, which is associated with cramps.
Result
will usually be abnormal in severe hepatic disease
serum myoglobin and urinalysis
Test
Elevated serum myoglobin with myoglobinuria, presenting with prominent muscle pain, should be considered in the differential diagnosis.
Urinalysis will help to determine whether a urine myoglobin test is needed (i.e., haem-positive with no RBCs on microscopy).
Result
present if muscle pain associated with myoglobin release and excretion
serum creatine kinase (CK)-MM
Test
Indicated only if history and/or physical examination suggests a potential primary muscle disease or patient is taking a statin.
In idiopathic muscle cramps, this should be normal. However, muscle cramps alone can precipitate increased serum CK concentrations. This does not necessarily imply a primary muscle disease as the aetiology.[83]
May be high levels of serum CK-MM in severe EAMC disease.
Elevated CK during statin therapy may indicate genetic predisposition to malignant hyperthermia.[84]
Chronic elevation of serum CK is not uncommon in familial muscle contraction syndromes (particularly glycogen storage disease, muscular dystrophy) and haemodialysis, both of which are commonly associated with muscle cramps.[85][86]
Beta-blockers with intrinsic sympathomimetic activity (such as pindolol, carteolol) can cause a chronic elevation of CK. These agents are among the drugs most frequently associated with causing muscle cramps. However, no correlation is seen between muscle cramp frequency/severity and the serum CK concentrations associated with them.[51]
Result
normal; may be elevated in severe exercise-associated muscle cramps (EAMC)
serum alpha-tocopherol (vitamin E)
Test
May be performed if considering preventative therapy in people with cramps associated with cirrhosis.
Result
may be low in cirrhosis
serum zinc
Test
May be performed if considering preventative therapy in people with cramps associated with cirrhosis.
Result
may be low in cirrhosis
electromyogram
Test
Performed only in difficult-to-diagnose cases or if lower motor neuron disease is suspected.
Result
motor unit hyperactivity
nerve conduction studies
Test
Performed if lower motor neuron disease suspected.
Result
lower motor neuron disease: may show loss of amplitude of maximal compound muscle action potential or slowed conduction velocity or conduction block; sensory nerves are unchanged
serum aldolase
Test
Indicated only if history and/or physical examination suggests a potential primary muscle disease.
In idiopathic muscle cramps should be normal.
Result
normal
muscle biopsy
Test
Indicated only if history and/or physical examination suggests a potential primary muscle disease.
A normal biopsy demonstrates fibres roughly equal in size, tightly opposed to each other, no fibrous tissue separating them, nuclei peripherally situated.[87]
Result
usually normal; lower motor neuron disease: may be evidence of denervation, group atrophy, fibre type grouping; may be evidence of primary muscle disease
genetic studies
Test
Generally requested only when a patient's symptoms are particularly difficult to diagnose or a familial cramping syndrome is suspected (e.g., muscular dystrophy, congenital myotonia, glycogen storage disease, continuous muscle fibre activity syndrome, Satoyoshi's syndrome, Schwartz-Jampel syndrome, or Brody's disease).
Result
normal or genetic abnormality of associated familial cramping condition
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