Diagnostic Tests For Dermatomyositis

There are no specific lab tests at this point in time. However, there is a constellation of a number of blood tests that helps to make the diagnosis of dermatomyositis in combination with the clinical signs and symptoms. As in other connective tissue disease the ESR (sedimentation rate) is often elevated.

If other connective tissue diseases are also present, then the ANA titer is often positive. One other immunological test that has been useful in recent years is the Jo-1 antibody test. These are autoantibodies against thymus antigens, which can be detected with an ELISA type screening test (Ref.2).

The literature has shown that these types of autoantibodies seem to be present more often in patients who develop pulmonary complications (interstitial pneumonitis), polyarthritis symptoms or subcutaneous calcifications (Ref. 3 and 4). The muscle enzymes (transaminases, creatinine kinase (CK), aldolase) are often markedly elevated and are useful to follow to monitor the success of treatment (Ref. 1, p.435).

If the physician finds that there are still doubts about the diagnosis a muscle biopsy can be obtained, which is always reliable and is the most definitive test. Electromyography studies, also called EMG tests, can aid in the diagnosis as there are fairly characteristic changes visible on this test. Occasionally an MRI scan can help to identify an area with edematous and inflammatory changes where a muscle biopsy can then lead to the definitive diagnosis of dermatomyositis. Even though only 15% of male patients will have an occult cancer, in all patients with dermatomyositis cancer screening should be done, just to play it safe.

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Disclaimer:

This outline is only a teaching aid to patients and should stimulate you to ask the right questions when seeing your doctor. However, the responsibility of treatment stays in the hands of your doctor and you.

References:

1.The Merck Manual, 7th edition, by M. H. Beers et al., Whitehouse Station, N.J., 1999. Chapter 50.

2. WA Schmidt et al. Clin Rheumatol 2000;19(5):371-377.

3. A Sauty et al. Eur Respir J 1997 Dec;10(12):2907-2912.

4. R Queiro-Silva et al. J Rheumatol 2001 Jun;28(6):1401-1404.

5. J Wada et al. Clin Exp Immunol 2001 May;124(2):282-289.

Last Modified: Jan. 30, 2007