Myopathy

Last updated: Friday, 21, January, 2011
CausesAppropriate Tests

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

See also Myoglobinuria

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

Inflammatory

FBC, blood film; CRP

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

Metabolic

 

 

 


Magnesium

Endocrine disorders

 

 

 

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 genetics) is available for some disorders.

  • Muscular dystrophy
  • Glycogen storage and glycolytic defects
  • Carnitine palmityl transferase deficiency
  • Carnitine deficiency
  • Periodic paralysis
    • Hypokalaemic
    • Hyperkalaemic
  • Mitochondrial myopathies
  • Congenital myopathy
    • Malignant hyperthermia
    • Central core disease

 

See Glycogen storage diseases

 

Measure potassium during episode of paralysis.

 

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