eMedicine Specialties > Rheumatology > Systemic Rheumatic Disease

Dermatomyositis: Differential Diagnoses & Workup

Author: Jeffrey P Callen, MD, Professor of Medicine, Chief, Division of Dermatology, University of Louisville School of Medicine
Contributor Information and Disclosures

Updated: Apr 14, 2009

Differential Diagnoses

Graft Versus Host Disease
Hypothyroidism
Multicentric Reticulohistiocytosis
Sarcoidosis

Other Problems to Be Considered

Calcinosis cutis, Raynaud phenomenon, esophageal motility disorder, sclerodactyly, and telangiectasia (CREST) syndrome
Inclusion body myositis
Lichen myxedematosus
Lichen planus
Systemic lupus erythematosus
Discoid lupus erythematosus
Subacute cutaneous lupus erythematosus
Morphea
Parapsoriasis
Pityriasis rubra pilaris
Polymorphous light eruption
Plaque psoriasis
Rosacea
Tinea corporis
Chronic urticaria

Workup

Laboratory Studies

  • Muscle enzyme levels are often abnormal during the course of dermatomyositis (DM), except in patients with the amyopathic variant. The most sensitive/specific enzyme is elevated creatine kinase (CK), but aldolase studies and other tests (eg, aspartate aminotransferase [AST], lactic dehydrogenase [LDH]) may also yield abnormal results. At times, the elevation of the enzymes precedes clinical evidence of myositis. Thus, if a patient who is presumably stable develops an elevation of an enzyme 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 ANA finding is common in patients with dermatomyositis.
    • Anti–Mi-2 antibodies are highly specific for dermatomyositis but lack sensitivity because only 25% of the patients with dermatomyositis demonstrate them. They are associated with acute-onset classic dermatomyositis with the V-shaped and shawl rash (poikiloderma) and a relatively good prognosis.
    • Anti–Jo-1 (antihistidyl transfer RNA [t-RNA] synthetase) is more common in patients with polymyositis than in patients with dermatomyositis. It is associated with pulmonary involvement (interstitial lung disease), Raynaud phenomenon, arthritis, and mechanic's hands.
    • Other MSAs include antisignal recognition protein (anti-SRP), associated with severe polymyositis, and anti–PM-Scl and anti-Ku, which are associated with overlapping features of myositis and scleroderma.

Imaging Studies

  • MRI
    • MRI may be useful in assessing for the presence of an inflammatory myopathy in patients without weakness.
    • MRI is useful in differentiating steroid myopathy from continued inflammation.
    • MRI may serve as a guide in selecting a muscle biopsy site.
  • Chest radiography should be obtained at the time of diagnosis and when symptoms develop.
  • A barium swallow allows evaluation of esophageal dysmotility.
  • Ultrasonography of the muscles has been suggested for evaluation but has not been widely accepted.
  • Electromyography is a means of detecting muscle inflammation and damage and, at times, has been useful in selecting a muscle biopsy site. This test is obtained less commonly since the introduction of muscle MRI.
  • CT scanning is useful in the evaluation of potential malignancy that might be associated with inflammatory myopathy.

Other Tests

  • Pulmonary function studies
  • Electrocardiography
  • Esophageal manometry - May be obtained in select patients

Procedures

  • Muscle biopsy, either open or 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.

Histologic Findings

Skin biopsy reveals an interface dermatitis that is difficult to differentiate from LE. Vacuolar changes of the columnar epithelium and lymphocytic inflammatory infiltrates at the dermal-epidermal junction basement membrane can occur.

The histopathology of dermatomyositis is an inter...

The histopathology of dermatomyositis is an interface dermatitis.

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The histopathology of dermatomyositis is an inter...

The histopathology of dermatomyositis is an interface dermatitis.


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

Histopathology of dermatomyositis showing inflamm...

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

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Histopathology of dermatomyositis showing inflamm...

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


More on Dermatomyositis

Overview: Dermatomyositis
Differential Diagnoses & Workup: Dermatomyositis
Treatment & Medication: Dermatomyositis
Follow-up: Dermatomyositis
Multimedia: Dermatomyositis
References
Further Reading
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References

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Further Reading

The reader is referred to articles by Callen and Wortmann (2006), 18 Iorizzo and Joizzo (2008), 19 and Krathen et al (2008) 20 for further reading.

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Keywords

dermatomyositis, idiopathic inflammatory myopathy, IIM, dermatomyositis sine myositis, amyopathic dermatomyositis, ADM, juvenile dermatomyositis, childhood dermatomyositis, DM, polymyositis, PM, DM-sine myositis, myositis with malignancy, childhood DM, childhood PM, myositis, postmyopathic DM, postmyopathic dermatomyositis, complement-mediated vascular inflammation, terminal attack complex, calcinosis, heliotrope rash, Gottron papules

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Contributor Information and Disclosures

Author

Jeffrey P Callen, MD, Professor of Medicine, Chief, Division of Dermatology, University of Louisville School of Medicine
Jeffrey P Callen, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Dermatology, American College of Physicians, and American College of Rheumatology
Disclosure: Amgen Honoraria Consulting; Abbott Honoraria Consulting; Electrical Optical Sciences Honoraria Consulting; Centocor Honoraria Consulting; Genetech Honoraria Consulting; Celgene Honoraria Consulting

Medical Editor

Kristine M Lohr, MD, MS, Program Director, Professor, Department of Internal Medicine, Division of Rheumatology and Women's Health, University of Kentucky School of Medicine
Kristine M Lohr, MD, MS is a member of the following medical societies: American College of Physicians, American College of Rheumatology, and American Medical Women's Association
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: Nothing to disclose.

Managing Editor

Lawrence H Brent, MD, Associate Professor of Medicine, Thomas Jefferson University; Chair, Program Director, Department of Medicine, Division of Rheumatology, Albert Einstein Medical Center
Lawrence H Brent, MD is a member of the following medical societies: American Association of Immunologists, American College of Physicians, and American College of Rheumatology
Disclosure: Genentech Honoraria Speaking and teaching; Genentech Grant/research funds Other; Amgen Honoraria Speaking and teaching; Wyeth Honoraria Speaking and teaching; Abbott Immunology Honoraria Speaking and teaching

CME Editor

Alex J Mechaber, MD, FACP, Associate Dean for Undergraduate Medical Education, Associate Professor of Medicine, University of Miami Miller School of Medicine
Alex J Mechaber, MD, FACP is a member of the following medical societies: Alpha Omega Alpha, American College of Physicians-American Society of Internal Medicine, and Society of General Internal Medicine
Disclosure: Nothing to disclose.

Chief Editor

Herbert S Diamond, MD, Professor of Medicine, Temple University School of Medicine; Chairman Emeritus, Department of Internal Medicine, Western Pennsylvania Hospital
Herbert S Diamond, MD is a member of the following medical societies: Alpha Omega Alpha, American College of Physicians, American College of Rheumatology, American Medical Association, and Phi Beta Kappa
Disclosure: medifocus Honoraria Review panel membership; health dialogs Honoraria Consulting; West Penn Allegheny Health System None Board membership

 
 
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