Marinos C Dalakas

Neuromuscular Diseases Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA

1. Introduction

Dermatomyositis (DM) is one of the three main inflammatory myopathies, the other two being poly-myositis and inclusion-body myositis (Dalakas, 1991; Dalakas, 2003). Although, it may have been recognized earlier by Wagner (1863), the first definitive description of DM was reported by Unverricht (1891). Before the extensive use of immunosuppressive drugs, DM was the cause of considerable disability and mortality, especially in children. During the last 30 years, the extensive use of these drugs and the better understanding of the immunopathology of the disease have significantly improved the prognosis. DM, a disease affecting skin and muscle, is cared for not only by neurologists but also by rheumatologists and dermatologists. The role of the physician is essential to exclude other diseases associated with skin and muscle pathologies, to establish the cause of the symptoms, to confirm the immune-basis of the disease, and supervise the immunotherapeutic interventions.

2. Epidemiology/Prevalence

The exact incidence of DM is unknown. Along with the other two forms of inflammatory myopathies

*Corresponding author.

Neuromuscular Diseases Section, NINDS, NIH, Building 10, Room 4N248, 10 Center Dr. MSC 1382, Bethesda, MD, 20892-1382, USA.

Tel.: +1-301-496-9979; Fax: + 1-301-402-0672. E-mail address: [email protected] (M.C. Dalakas).

(polymyositis and inclusion-body myositis), they occur in approximately 1 in 100,000 adults.

3. Etiology

3.1. Overlap syndromes

''Overlap syndrome'' defines a disorder that shares the characteristics of two usually distinct disorders. As such, DM truly overlaps with two connective tissue disorders, scleroderma and mixed connective tissue disease. Specific signs of systemic sclerosis or mixed connective tissue disease such as sclerotic thickening of the dermis, contractures, esophageal dysmotility, microangiopathy, and calcium deposits are present only in DM but not in other inflammatory myopathies. Conversely, signs of rheumatoid arthritis, systemic lupus ery-thematosus, or Sjogren syndrome are very rare in DM. Patients with the overlap syndrome of DM/systemic sclerosis may have an antinuclear autoantibody, the anti-polymyositis/Scl, directed against a nucleolar protein complex.

3.2. Viruses

Coxsackie viruses, influenza, vaccinations, or even retroviruses have been proposed as possible causes of DM. However, there are no signs to indicate that they play a pathogenic role in the disease, and their association has been peripheral and circumstantial. All attempts to isolate viruses, including retroviruses, from the patients' muscle or amplify viral products by polymerase chain reaction have been unsuccessful.

3.3. Cancer

The incidence of malignancies is increased in patients with DM (Buckbinder et al., 2001; Hill et al., 2001). Ovarian cancer is most frequent, followed by intestinal, breast, lung, and liver cancer. In Asian populations, nasopharyngeal cancer is more common. In general, however, the cancer sites correspond to those occurring more frequently at the patient's age (Callen, 2002). Because tumors are often uncovered at autopsy or on the basis of abnormal findings on medical history and physical examination, blind radiologic searches are rarely fruitful. A complete annual physical examination with breast, pelvic, and rectal examinations (including colonoscopy in high-risk patients), urinalysis, complete blood-cell count, blood chemistry tests, and chest X-ray, is usually sufficient and is highly recommended especially during the first 3 years.

3.4. Myotoxic drugs

There are anecdotal reports that some cholesterol lowering drugs may cause disease resembling DM. Three cases, one with pravastatin, another with simvastatin, and a third with atorvastatin (Schalke et al., 1992; Khattak et al., 1994; Noel et al., 2001) suggest that these agents are not only myotoxic but they can also affect the skin in a DM-like pattern and induce an inflammatory response in susceptible individuals.

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