Dermatomyositis Workup

Updated: Sep 26, 2018
  • Author: Alisa N Femia, MD; Chief Editor: Herbert S Diamond, MD  more...
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Workup

Approach Considerations

The workup for dermatomyositis may include selected laboratory tests and diagnostic imaging (eg, magnetic resonance imaging [MRI], chest radiography, ultrasonography, electromyography [EMG], or computed tomography [CT]), as well as muscle and skin biopsy and other tests as appropriate.

In adult patients with dermatomyositis, assessment for malignancy should be performed upon initial diagnosis and repeated at least annually for 3 years. The risk of malignancy increases with age. The exact testing order should be based on the patient's sex, age, and race; however, testing beyond age-appropriate screening is most often recommended.

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Laboratory Studies

Muscle enzyme levels are often abnormal during the course of dermatomyositis, except in patients with amyopathic dermatomyositis (ADM). The most sensitive/specific enzyme abnormality is elevated creatine kinase (CK), but aldolase studies and other tests (eg, for aspartate aminotransferase [AST] or lactic dehydrogenase [LDH]) may also yield abnormal results.

At times, the elevation of the enzymes precedes the appearance of clinical evidence of myositis. Thus, if a patient who is presumably stable develops an elevation of an enzyme that was previously within the reference range, the clinician should assess the possibility of a flare of the muscle disease.

Several serologic abnormalities have been identified and may be helpful in the classification of subtypes for prognosis, but they are not used for routine diagnosis. As a group, these antibodies have been termed myositis-specific antibodies (MSAs). These autoantibodies occur in about 30% of all patients with dermatomyositis or polymyositis.

A positive antinuclear antibody (ANA) finding is common in patients with dermatomyositis, but is not necessary for diagnosis.

Anti–Mi-2 antibodies are highly specific for dermatomyositis, but sensitivity is low; only 25% of patients with dermatomyositis demonstrate these antibodies. These autoantibodies are associated with acute-onset classic dermatomyositis, including the V-neck sign and shawl rash (poikiloderma), as well as a relatively good prognosis.

Anti–Jo-1 (antihistidyl transfer RNA [t-RNA] synthetase) antibodies are more common in patients with polymyositis, but may occur in patients with dermatomyositis. They are associated with pulmonary involvement (interstitial lung disease), Raynaud phenomenon, arthritis, and mechanic's hands in the setting of the anti-synthetase syndrome.

Other MSAs include anti-signal recognition protein (anti-SRP), which is associated with severe myositis; anti–PM-Scl and anti-Ku, which are associated with overlapping features of myositis and scleroderma; and anti-NXP-2, which is associated with calcinosis in the juvenile population, and more recently, in the adult population as well. [42]

An autoantibody directed against a 155-kd protein known as anti-p155/140 or antitranscription intermediary factor (TIF)-1γ, has been associated with malignancy in dermatomyositis. [49, 50, 51] Subsequently, the presence of anti-p155/140 antibodies targeting TIF-1α in addition to TIF-1γ, rather than TIF-1γ alone, was shown to be associated with malignancy. [52] Although these findings may be used to help prognosticate patients with dermatomyositis in the future, these antibodies may be found in patients without cancer, [52] and serology is not currently used routinely to help diagnose cancer-associated dermatomyositis.

A 140-kd polypeptide autoantibody, known as anti-CADM140 or antimelanoma differentiation antigen (MDA)–5, has been associated with clinically amyopathic dermatomyositis (CADM) and rapidly progressive interstitial lung disease, especially, but not exclusively, in the Asian population. [53, 54, 55, 56, 57, 58] In the United States population, skin and mucosal ulcerations and/or tender palmar papules (which are likely due to vasculopathy), along with hair loss, hand swelling, and arthritis/arthralgias, have been associated with circulating anti-MDA5 antibodies. [59]

A study of 11 patients with CADM suggests that levels of anti-MDA5 antibodies may fluctuate over time and may correlate with disease activity. [60] In addition, in the juvenile dermatomyositis population, anti-(MDA)-5 antibodies were recently found to be associated with skin and oral ulceration, arthritis, and milder muscle involvement in a cohort of United Kingdom patients. [61]

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Imaging Studies

MRI may be useful in assessing for the presence of an inflammatory myopathy in patients without weakness. It can assist in differentiating steroid myopathy from continued inflammation and may serve as a guide in selecting a muscle biopsy site. Ultrasonography of the muscles has also been suggested for evaluation but has not been widely accepted.

Electromyography (EMG) is a means of detecting muscle inflammation and damage and has, at times, been useful in selecting a muscle biopsy site. Since the introduction of muscle MRI, EMG has been obtained less commonly in this setting.

A barium swallow allows evaluation of esophageal dysmotility.

CT scanning of the chest, abdomen, and pelvis is useful in the evaluation of potential malignancy that might be associated with dermatomyositis.

Transvaginal ultrasonography of the pelvis is particularly important for malignancy screening in women, given the strong association between ovarian cancer and dermatomyositis. Mammography is also useful in women for the evaluation of a potential malignancy.

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Other Studies

Other tests may include the following:

  • Muscle biopsy

  • Pulmonary function studies with diffusion capacity

  • Electrocardiography (ECG)

  • Esophageal manometry (in selected patients)

  • Age-related colonoscopy and fecal-occult blood testing for malignancy screening

  • Papanicolaou smear in women for malignancy screening

  • Cancer antigen 125 (CA-125) and CA-19-9 for malignancy screening

Muscle biopsy, either open or via needle, may enhance the clinician's ability to diagnose dermatomyositis. The biopsy results may be useful in differentiating steroid myopathy from active inflammatory myopathy when patients have been on corticosteroid therapy but are still weak.

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Histologic Findings

Skin biopsy reveals an interface dermatitis that is difficult to differentiate from lupus erythematosus (see the image below). [62] Vacuolar changes of the columnar epithelium and lymphocytic inflammatory infiltrates at the dermal-epidermal junction basement membrane can occur. Mucin deposition in the dermis is also characteristic.

Histopathology of dermatomyositis is interface der Histopathology of dermatomyositis is interface dermatitis.

Findings on muscle biopsy can be diagnostic. Muscle biopsy in patients with dermatomyositis reveals perivascular and interfascicular inflammatory infiltrates with adjoining groups of muscle fiber degeneration/regeneration (see the image below). This contrasts with polymyositis infiltrates, which are mainly intrafascicular (endomysial inflammation) with scattered individual muscle fiber necrosis.

Histopathology of dermatomyositis showing inflamma Histopathology of dermatomyositis showing inflammatory myopathic changes with a predominantly perivascular chronic inflammatory infiltrate.

Although inflammation is the histologic hallmark of dermatomyositis, polymyositis, and inclusion-body myositis, dermatomyositis is the only 1 of the 3 that shows perifascicular atrophy. In addition, many fibers undergo degeneration and necrosis that cause them to lose their staining ability; therefore, they are termed ghost fibers. When these changes are associated with collections of inflammatory cells around the blood vessels, the diagnosis of dermatomyositis is certain (see the images below).

Hematoxylin and eosin paraffin shows dermatomyosit Hematoxylin and eosin paraffin shows dermatomyositis. In dermatomyositis, inflammation is characteristically perivascular and perimysial. Vessel oriented approximately vertically in center has mild perivascular chronic inflammatory infiltrate. Endothelium is plump; wall is not necrotic. A few lymphocytes in wall of vessel are probably in transit from lumen to external aspect of vessel. Some observers may interpret this finding as vasculitis, but it is certainly neither necrotizing vasculitis nor arteritis. Image courtesy of Roberta J. Seidman, MD.
Hematoxylin and eosin frozen section shows perifas Hematoxylin and eosin frozen section shows perifascicular atrophy in dermatomyositis. Fascicles in this sample show atrophy, predominantly at periphery, along connective-tissue border. Ischemia is considered to cause perifascicular atrophy. This finding is characteristic of dermatomyositis, mostly associated with juvenile form but also observed in adult form. Image courtesy of Roberta J Seidman, MD.
Immunofluorescence for membrane attack complex of Immunofluorescence for membrane attack complex of complement (MAC) in dermatomyositis. Bright ring of yellow-green fluorescence at center represents MAC in wall of microvessel. Finding was not present after treatment with steroids. Image courtesy of Roberta J Seidman, MD.
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Other Tests

The Cutaneous Dermatomyositis Disease Area and Severity Index (CDASI) is a clinical tool used to assess disease activity in cutaneous dermatomyositis. The CDASI has been validated for use by dermatologists, and more recently has also been shown to be a reliable measure when used by rheumatologists. [63]

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