Investigations
1st investigations to order
serum creatine kinase (CK)
genetic testing
Test
Genetic testing is an essential component for the diagnosis of DMD, other muscular dystrophies, and spinal muscular atrophy.[1][3][10][18][21][23]
When DMD is suspected, testing for deletion or duplication of the dystrophin-encoding DMD gene is carried out first, preferably using multiplex ligation-dependent probe amplification or array comparative genome hybridisation. If no mutation is detected, this is followed by detailed genetic sequencing to analyse other, less common mutations associated with DMD.[11][24]
Genetic testing should also be offered to family members, with appropriate pre- and post-test counselling.[23]
Result
Xp21 mutation may be present in DMD and Becker muscular dystrophy
Investigations to consider
electromyogram (EMG)
Test
If DNA studies for DMD are negative, EMG and muscle biopsy may be considered. EMG can usually distinguish between neuropathic and myopathic pathology. After a myopathic EMG, muscle biopsy is usually the next step in diagnosis. A neurogenic EMG usually leads to consideration of spinal muscular atrophy and polyneuropathies.
Result
myopathic reading with fast firing, short duration but polyphasic and decreased amplitude motor units with early recruitment in the affected muscles
muscle biopsy
Test
When DNA analysis does not identify the mutation and the mother or other family members are unavailable for linkage studies, muscle biopsy can establish the diagnosis. This is not routinely needed but is used often when genetics are negative, when the phenotype does not fit with the genetic change detected.
Routine histochemistry, immunohistochemistry (assessing dystrophin, sarcoglycans, alpha dystroglycan, merosin, caveolin 3, dysferlinA), and immunoblot testing (for dystrophin, dysferlin, and caplain) are performed on muscle biopsy specimens.[25]
Other proteins may be tested for in selected cases (e.g., emerin for Emery-Dreifuss muscular dystrophy, or dystroglycans in dystroglycanopathies).[1]
Result
absence of dystrophin with DMD; diminished quantity or quality of dystrophin with Becker muscular dystrophy; other specific defective or absent glycoproteins in the membrane of the muscle wall with other muscular dystrophies
muscle MRI
Test
Helpful for diagnosis of some muscular dystrophies. May also be used to assess disease progression.[1]
Result
shows distinctive pattern of selective muscle involvement
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