Differentials
Tetany
SIGNS / SYMPTOMS
Produces a characteristic motor posture known as carpopedal spasm.
Hypocalcaemic tetany: tingling begins around the mouth and in the peripheral extremities then increases in intensity and spreads proximally. A sensation of spasm or tension follows the same pattern as the tingling, eventually producing a tonic spasm. If severe, proximal and paraspinal muscles may be involved. Laryngeal muscles are commonly involved early. On examination, positive Trousseau's sign and Chvostek's sign are suggestive of neural hyperexcitability.
INVESTIGATIONS
Typical clinical findings with an associated electrolyte abnormality (either hypocalcaemia, hypomagnesaemia, or alkalosis).
There may also be hypokalaemia or hyperkalaemia.
Electromyogram findings: individual motor units discharge independently at a rate of 5 to 25 Hz (each discharge is a group of ≥2 identical potentials).
Tetanus
SIGNS / SYMPTOMS
Primary symptoms are muscular rigidity and spasms. Trismus and dysphagia are typical.
The spasms, which are extremely painful, are caused by sudden, involuntary contractions of opposing muscles that last for only a few seconds but occur repeatedly for minutes.
Spasms are localised or generalised and can be triggered by sensory stimuli, movement, or emotion.
In some cases, spasms are severe enough to cause muscle injury or to fracture bones.
INVESTIGATIONS
Diagnosed clinically.
No specific change found in blood, urine, or cerebrospinal fluid.
No specific confirmatory laboratory test (absence of serum tetanus toxin or a negative result from clostridial culture testing does not rule out infection).
Occupational cramps
SIGNS / SYMPTOMS
Muscular contractions without pain.
A type of dystonia and not cramp.
Task-specific, arising due to repetitive or skilled use of a body part (e.g., hands [hairstylists, musicians, court reporters], mouth [musicians playing wind instruments]).
Begin in adulthood.[88]
INVESTIGATIONS
No distinguishing tests.
Restless legs syndrome
SIGNS / SYMPTOMS
Urge to move legs with or without paresthesias when relaxing or attempting to sleep. Resolves when patient begins activity.[89] Muscle hardening is not usually present.
INVESTIGATIONS
No differentiating tests.
Growing pains
SIGNS / SYMPTOMS
Not associated with palpable/visible hardening of muscle usually seen with cramps.
Most common sites of pain are shins and calves.
Pain lasts between a few minutes and a few hours.
Occurs at night and usually disappears by the morning.[90]
INVESTIGATIONS
No differentiating tests.
Neuromyotonia (e.g., Isaac's syndrome)
SIGNS / SYMPTOMS
Predisposes to true muscle cramps.
However, other clinical manifestations of this disorder of continuous muscle fibre activity are usually even more prominent.
All cases of neuromyotonia have visible continuous muscle 'worm-like movements' (myokymia).
Abnormal limb posturing, identical to carpal or pedal spasm, are characteristic and may be persistent or intermittent.
There is difficulty in relaxing the muscle (which differs from true myotonia), a lack of percussion myotonia, and increased rather than decreased stiffness with continued activity.
In children and young adults it progresses insidiously.
INVESTIGATIONS
Associated with the presence of serum antibodies to voltage-gated potassium channels.
Continuous muscle fibre activity syndromes (not neuromyotonia)
SIGNS / SYMPTOMS
Slow muscle relaxation after contraction as well as non-muscular findings (autonomic findings [e.g., hyperhidrosis, hypersalivation, and hyperlacrimation]).
May be associated with autoimmune phenomena such as myasthenia gravis and thymoma.[91]
INVESTIGATIONS
Electromyogram demonstrates myokymic and neuromyotonic discharges.
Autoantibodies to antigens on peripheral motor neurons and autonomic fibres.
Multiple sclerosis
SIGNS / SYMPTOMS
Common symptoms include visual disturbance, sensory phenomena (e.g., sensations of wetness or burning, hemibody sensory loss or tingling, Lhermitte’s sign [electric shock-like sensations extending down the cervical spine radiating to the limbs]), progressive limb weakness, gait difficulty, ataxia, sphincter and sexual dysfunction, fatigue.
INVESTIGATIONS
Brain MRI with gadolinium enhancement typically shows areas of demyelination; sagittal fluid-attenuated inversion recovery images are the most sensitive.
Cerebrospinal fluid (CSF) analysis: oligoclonal bands and elevated CSF IgG and IgG synthesis rate may be present.
Somatosensory, visual evoked, and brainstem auditory evoked potentials are prolonged.
Dystrophinopathies (e.g., Duchenne's or Becker's muscular dystrophy)
SIGNS / SYMPTOMS
May be a family history of the condition.
Loss of ability to walk by about 12 years old (Duchenne's).
Contractures of hips, knees, ankles. Severe scoliosis.[87]
INVESTIGATIONS
DNA studies may detect deletion of dystrophin gene.
Abnormal electrocardiogram due to degeneration and fibrosis of posterolateral aspect of left ventricular wall.
Echocardiogram may show abnormal valve and wall motion, cardiomyopathy.
Serum creatine kinase levels are markedly increased.
Electromyogram may reveal myopathic changes.
Muscle biopsy may show variation in fibre sizes, fibrosis, and basophilic and hyaline fibres in groups.
Myotonic dystrophies
SIGNS / SYMPTOMS
Myotonia is characterised by slowing in the relaxation of muscles after voluntary contraction or electrical stimulation.
Dystrophies characterised by weakness of hand, feet, neck muscles; hollowing of temples due to masseter and temporalis atrophy.
Shoulder, hip, leg weakness can lead to repeated falls.
Demonstration of myotonia by sharp percussion of muscle with reflex hammer or after firm voluntary contraction.
Cardiomyopathy; excessive daytime somnolence and cataracts.[87]
INVESTIGATIONS
DNA studies may detect mutations of myotonic muscular dystrophy protein kinase (DMPK) gene.
Muscle biopsy may show variability in fibre size, fibrosis, and ring fibres.
Electromyogram may show myotonic discharges (repetitive firing of muscle fibres at 20 to 80 Hz with waxing/waning of the amplitude/frequency).
Satoyoshi's syndrome
SIGNS / SYMPTOMS
Alopecia, diarrhoea, endocrinopathy with amenorrhoea, and secondary skeletal abnormalities, in addition to painful muscle spasms.[92]
Syndrome usually develops between 6 and 15 years of age, with alopecia and leg spasms initially.
INVESTIGATIONS
Clinical diagnosis.
Brody's disease
SIGNS / SYMPTOMS
Difficulty with walking and climbing stairs.
Enhanced fatigueability during exercise.
Painless contractures (stiffness) during exercise.
Increased exercise intolerance in cold environment.[93][94][95]
INVESTIGATIONS
Muscle biopsy may be sent for analysis of microsomal calcium uptake, which shows a significant decrease compared with controls.
Electromyogram shows impaired relaxation of agonist muscles, with substantial electrical activity of antagonist muscles at the same time.
DNA analysis detects deficiency of gene for sarcoplasmic reticulum adenosine triphosphate-dependent calcium pump.
Swartz-Jampel syndrome
SIGNS / SYMPTOMS
Facial malformations (microstomia, micrognathia, retrognathia, short palpebral fissures, low-set ears, short neck).
Musculoskeletal signs, including myopathy, myotonia, muscle hypertrophy, restricted joint mobility, kyphosis, scoliosis, pectus carinatum, anterior bowing of long bones.
Areflexia or hyporeflexia, cognitive dysfunction.[96]
INVESTIGATIONS
DNA analysis for gene causing abnormal proteoglycan of basement membranes.
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