Muscular Dystrophy Workup

Updated: Jul 01, 2021
  • Author: Twee T Do, MD; Chief Editor: Jeffrey D Thomson, MD  more...
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Workup

Laboratory Studies

A creatine phosphokinase (CPK) determination is the most specific test for muscular dystrophy (MD). Elevated CPK levels are indicative of muscle disease. Because the concentration of CPK is not significant in red blood cells, CPK levels are not affected by hemolysis. CPK is not affected by liver dysfunction, as are the other tested enzymes (eg, transaminases, aldolase, lactate dehydrogenase). High CPK levels represent leakage of the enzyme from the muscle cells only. This change is not exactly correlated with the severity of the disease.

All MDs result in some CPK elevation during the active phase of the disease. The finding of three elevated levels obtained 1 month apart is diagnostic for MD. Early in the disease process, CPK levels are 50-300 times greater than normal levels, but the levels tend to decrease as the muscle mass decreases. The CPK level is highest in Duchenne MD, with less elevation noted in Becker MD.

Enzyme levels that may be elevated but can be altered by liver dysfunction include the following:

  • Transaminase levels
  • Lactate dehydrogenase levels
  • Aldolase levels

The multiplex polymerase chain reaction (PCR) assay may be useful. PCR was developed by Chamberlain et al, [31] who noted that deletions of the dystrophin gene tend to cluster around two hot-spot regions: at exons 3-30 and at exons 44-55. [32]  The PCR method rapidly screens for deletions of the dystrophin gene by applying PCR to amplify the DNA in the hot-spot regions and by simultaneously using a number of appropriate primers that flank these hot-spot regions. PCR can be used to detect more than 98% of existing deletions, and it can be performed within 24 hours.

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Imaging Studies

Ultrasonography (US) is a relatively noninvasive technique that is used for screening patients with MD; this modality is rapidly replacing electromyography (EMG) in centers that have appropriately trained staff. Even in the early stages of MD, US shows increased echogenicity in the affected muscles, with a corresponding reduction in the underlying bone echo. US has the advantage of noninvasiveness, and it is reliable for continued monitoring of the disease course over time.

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Other Tests

Electrocardiography (ECG) is expected to show a right ventricular strain, tall R waves, deep Q waves, and inverted T waves. A cardiologist should be consulted preoperatively because cardiac management may be necessary in the postoperative care of dystrophic patients.

Pulmonary function tests (PFTs), including an analysis of arterial blood gases, and a hematologic workup are necessary as part of the preoperative workup. A pulmonologist may be consulted preoperatively because he or she can be helpful in managing the patient's airway in the postoperative period.

EMG usually demonstrates short-duration, polyphasic, motor-unit action potentials with decreased amplitudes. It should be kept in mind that this finding is common with all myopathic processes and does not specifically identify MDs.

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Biopsy

Until the advent of molecular biology techniques, muscle biopsy was the definitive test for diagnosing and confirming muscular disease. Histologic changes depend on the stage of disease and the muscle selected. The optimal site for biopsy is the vastus lateralis, accessed via a small lateral thigh incision.

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Histologic Findings

Histologic specimens from muscle biopsy samples obtained early in the muscular dystrophy disease show only variations in muscle fiber sizes with focal areas of degenerating or regenerating fibers. In later stages of MD, the changes are more obvious, with marked variations in muscle fiber sizes, degeneration, and regeneration. Rounded opaque fibers, internal nuclei, splitting of fibers, and a proliferation of connective and adipose tissues are also present. As the disease progresses, fewer and fewer regenerative fibers are seen. In the end phase, the muscle is mostly replaced by adipose tissue, with residual islets of muscle fibers in a sea of fat.

Histochemical staining with the standard adenosine triphosphatase (ATPase) reaction shows a predominance of type I muscle fibers, with loss of clear-cut distinction into the various fiber types. Electron microscopy demonstrates nonspecific degeneration of the fibers, and immunocytochemical techniques show a persistence of fetal and slow myosin in many of these fibers. (See the images below.)

Gomori trichrome–stained section in patient with m Gomori trichrome–stained section in patient with myofibrillar myopathy. Note the abnormal accumulations of blue-red material in several muscle fibers.
Left: The photomicrograph is a muscle biopsy with Left: The photomicrograph is a muscle biopsy with normal emerin immunostaining. Right: The micrograph is from a patient with X-linked Emery-Dreifuss muscular dystrophy. Note the absence of nuclear staining as well as the hypertrophied and atrophied muscle fibers.
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