Myopathy

Causes

Appropriate Tests

 

Review clinical features especially associated disease; drug therapy; presence of myotonia, myasthenia or cardiomyopathy; history of red-brown urine (myoglobinuria). 

See also Myoglobinuria.

Creatine kinase is usually elevated but the degree of elevation does not necessarily correlate with the severity of muscle weakness.

Inflammatory

  • Polymyositis / dermatomyositis
  • Connective tissue diseases
  • Malignancy
  • Sarcoidosis

Full blood count, Blood film; C-Reactive protein

Extractable nuclear antigen Ab, Jo-1 Ab. Muscle biopsy (consult pathologist prior to procedure).

Metabolic

  • Alcoholism
  • Hypokalaemia
  • Hyperkalaemia
  • Hypocalcaemia
  • Hyponatraemia
  • Hypermagnesaemia

 

 

 


Magnesium

Endocrine disorders

  • Hypothyroidism
  • Hyperthyroidism
  • Cushing's syndrome
  • Diabetes mellitus
  • Addison's disease

 

 

 

See under Adrenocortical insufficiency

Drug reactions

  • Penicillamine
  • Clofibrate
  • HMGCoA reductase inhibitors
  • Corticosteroids

 

Muscle wasting secondary to severe, systemic illness

 

Hereditary

Muscle biopsy, including chemical pathology studies, may be helpful (consult pathologist prior to procedure as special collection techniques are required for open biopsies).

Prenatal diagnosis (including Molecular genetic analysis) is available for some disorders.

  • Muscular dystrophy
 
  • Glycogen storage and glycolytic defects

See Glycogen storage diseases

  • Carnitine palmityl transferase deficiency
  • Carnitine deficiency

 

Periodic Paralysis

  • Hypokalaemic
  • Hyperkalaemic

Measure Potassium during episode of paralysis.

  • Mitochondrial myopathies
  • Congenital myopathy
    • Malignant hyperthermia
    • Central core disease

See Mitochondrial disorders
Muscle biopsy assists in identification of most types, but cannot specifically identify malignant hyperthermia.