Diagnosis

Diagnosis of McArdle's disease is based on :

(i) clinical picture

(ii) absence of increased venous lactate during forearm ischaemic exercise test

(iii) low or absent myophosphorylase activity on histochemical or biochemical examination of muscle biopsy

(iv) genetic testing

DNA analysis should allow diagnosis of the disease from peripheral lymphocytes thus rendering the muscle biopsy obsolete.

Notes:

• transient, repetitive hyper-CKaemia associated with pyrexia may be caused by several myopathies
• the differential diagnosis includes:
  • metabolic myopathies such as mitochondrial myopathy
  • glycogen storage myopathy
  • impaired fatty acid and organic acid metabolism
  • endocrine myopathies such as thyroid myopathy
  • preclinical stage or carrier for muscular dystrophy
  • congenital myopathies
  • inflammatory myopathies
  • malignant hyperthermia.