Investigations

The diagnosis of Duchenne's muscular dystrophy is suggested by the finding of serum creatine kinase 30 to 200 times higher than normal, myopathic changes on electromyography and characteristic findings on muscle biopsy. Note that the serum creatine kinase is raised before the muscular weakness becomes clinically evident.

Note that the serum creatinine is also slightly raised in female carriers.

It is possible to do chromosomal analysis of the deleted part of the genome - chromosome Xp21 - and get a genetic confirmation of the disease

• approximately 70% of DMD cases are caused by a single or multi-exon deletion or duplication detectable by multiplex ligation dependent probe amplification (MLPA)
  • full sequencing of the dystrophin gene can detect small genetic changes, such as point mutations, when DMD is still suspected but MLPA has failed to identify an abnormality

Notes:

• a mildly raised creatine kinase level of 1-2 times the normal range should be confirmed through a repeated test and followed up
  • a normal creatine kinase result excludes DMD - however not all neuromuscular conditions are associated with elevated creatine kinase (2)
    • guidance suggests that if you suspect a muscle problem but creatine kinase levels are within the normal range, a referral to a neuromuscular specialist may still be warranted

Reference:

• Rodger S et al. Adult care for Duchenne muscular dystrophy in the UK. J Neurol. 2015; 262(3): 629–6
• Fox H et al. Duchenne muscular dystrophy. BMJ 2020;368:l7012
• Lisak RP, Truong DD, Carroll W, Bhidayasiri R (2011). International Neurology. Wiley. p. 222. ISBN 9781444317015.