eMedicine Specialties > Emergency Medicine > Allergy & Immunology
Polymyositis: Differential Diagnoses & Workup
Updated: Aug 25, 2009
- Overview
- Differential Diagnoses & Workup
- Treatment & Medication
- Follow-up
- Multimedia
Differential Diagnoses
Other Problems to Be Considered
Vasculitis
Progressive systemic sclerosis
Infectious myositis
Muscular dystrophy
Eaton-Lambert syndrome
Drug-induced myopathies - Corticosteroids, statins, zidovudine
Electrolyte disorders
Inherited myopathies
Workup
Laboratory Studies
- Creatine kinase, aldolase, myoglobin, lactate dehydrogenase, aspartate aminotransferase, and alanine aminotransferase levels may be elevated.
- In practice, usually only the creatine kinase and aldolase levels are determined. The creatine kinase level is the most sensitive and specific; it usually is 5-50 times above the reference level. A level greater than 100 times the reference level is rare and is a signal of other diagnoses.
- The erythrocyte sedimentation rate usually is elevated.
- Myoglobinuria may be present.
- Positive rheumatoid factor results are found in more than 50% of patients.
- Positive antinuclear antibody results are found in fewer than 50% of patients.
- Leukocytosis is present in more than 50% of patients.
Imaging Studies
- MRI examination
- MRIs show signal intensity abnormalities of muscle due to inflammation, edema, or scarring.
- Images may be used to guide muscle biopsy.
- Many clinicians choose the biopsy site on the basis of findings at electromyography and clinical examination and believe that MRIs are not required.
MRI of thighs showing increased signal in the quadriceps muscles bilaterally consistent with inflammatory myositis.
- Chest radiography - Radiographs may show evidence of pulmonary involvement or associated malignancy.
- Consider mammography and pelvic ultrasonography in screening for associated malignancy.
- Testing for associated malignancy is based on age and sex and may also include upper and lower gastrointestinal endoscopy.
Other Tests
- Electromyographs reveal characteristic myopathic abnormalities.
- Electrocardiography may reveal arrhythmias or conduction disturbances.
Procedures
- Inflammatory changes are seen at muscle biopsy (eg, deltoid or quadriceps femoris). Findings occasionally may be normal because of patchy involvement. A biopsy should not be performed on muscle that has undergone electromyography. Diagnostic errors are minimized by combining muscle biopsy results with clinical and laboratory findings.
Hematoxylin and eosin paraffin section shows polymyositis. Patient had dense endomysial inflammation that contains an abundance of plasma cells, which can be observed in patients with chronic polymyositis. Two necrotic myofibers, characterized by dense eosinophilic staining, are observed. Focal fatty infiltration of the muscle is present in the lower left quadrant of the photomicrograph. Image courtesy of Roberta J. Seidman, MD.
Hematoxylin and eosin paraffin section shows polymyositis. Photomicrograph illustrates attack on a nonnecrotic myofiber by autoaggressive T lymphocytes. On the left, the central myofiber is intact. On the right, it is obliterated by a segmental inflammatory attack. If immunohistochemistry were performed, expected findings would include an admixture of CD8 T lymphocytes and macrophages in the inflammatory process. Image courtesy of Roberta J. Seidman, MD.
Hematoxylin and eosin paraffin shows dermatomyositis. In dermatomyositis, inflammation is characteristically perivascular and perimysial. Vessel oriented approximately vertically in the center has a mild perivascular chronic inflammatory infiltrate. The endothelium is plump. The wall is not necrotic. A few lymphocytes in the wall of the vessel are probably in transit from the lumen to the external aspect of the 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.
More on Polymyositis |
| Overview: Polymyositis |
 Differential Diagnoses & Workup: Polymyositis |
| Treatment & Medication: Polymyositis |
| Follow-up: Polymyositis |
| Multimedia: Polymyositis |
| References |
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References
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Hengstman GJ, van Engelen BG. Polymyositis, invasion of non-necrotic muscle fibres, and the art of repetition. BMJ. Dec 18 2004;329(7480):1464-7. [Medline]. [Full Text].
Koopman WJ. Polymyositis/dermatomyositis classification criteria. In: Arthritis and Allied Conditions. 1997:17-8.
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Nirmalananthan N, Holton JL, Hanna MG. Is it really myositis? A consideration of the differential diagnosis. Curr Opin Rheumatol. Nov 2004;16(6):684-91. [Medline].
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Further Reading
Keywords
polymyositis, PM, dermatomyositis, DM, inclusion body myositis, idiopathic inflammatory myopathy, inflammatory muscle disease, immune-mediated muscle inflammation, proximal muscle weakness, dysphagia, aspiration, arthralgias, muscle atrophy, heliotrope rash, purple-red edematous periorbital eruption, scaly purple-erythematous papular eruption over knuckles, Gottron sign, conduction defects, arrhythmias, myocarditis, interstitial lung disease, aspiration pneumonia, skeletal muscle disease
