eMedicine Specialties > Rheumatology > Systemic Rheumatic Disease
Polymyositis: Differential Diagnoses & Workup
Updated: Nov 6, 2009
- Overview
- Differential Diagnoses & Workup
- Treatment & Medication
- Follow-up
- Multimedia
Differential Diagnoses
| Cushing Syndrome | Polymyalgia Rheumatica |
| Fibromyalgia | Sarcoidosis |
| Hyperthyroidism | Systemic Lupus Erythematosus |
| Hypothyroidism | Trichinosis |
Other Problems to Be Considered
- Other idiopathic inflammatory myopathies
- Inclusion body myositis
- Eosinophilic myositis
- Myositis ossificans
- Focal myositis
- Giant cell myositis
- Amyotrophic lateral sclerosis
- Diabetic polyradiculopathy
- Drug-induced myopathy
- Alcohol
- Antimalarials
- Clofibrate
- Colchicine
- Ketoconazole and other azole antifungal agents
- Statin/3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors
- D-penicillamine
- Vincristine
- Zidovudine (AZT)
- Metabolic myopathy
- Muscular dystrophy
- Myasthenia gravis
- Overlap connective-tissue diseases
Workup
Laboratory Studies
- Serum creatine kinase (CK) levels are usually elevated in persons with polymyositis, ranging from 5-50 times the reference range. Serum CK levels, along with careful physical examination, may be used to monitor myositis activity. However, serum CK levels may be within reference ranges despite increased disease activity (eg, in cases of chronic and late-stage polymyositis [PM]). CK levels are usually minimally elevated or within the reference range in patients with inclusion body myositis. CK levels are within the reference range in patients with corticosteroid-induced myopathy.
- Other muscle enzymes may be elevated.
- Lactic dehydrogenase
- Aspartate aminotransferase
- Alanine aminotransferase
- Aldolase
- Nonspecific markers of inflammation include the following:
- CBC count may show leukocytosis or thrombocytosis.
- The erythrocyte sedimentation rate or C-reactive protein level is elevated in 50% of patients with polymyositis.
- Antinuclear antibody assay findings are positive in one third of patients with polymyositis and in only 15% of patients with inclusion body myositis.
- Myositis-specific antibodies are associated with polymyositis.
- Antisynthetase antibodies, such as anti-Jo-1 antibodies, are associated with certain clinical features. Antisynthetase syndrome may manifest as idiopathic inflammatory myopathy, interstitial lung disease, arthritis, Raynaud phenomenon, fever, and/or mechanic's hands.
- Approximately 4% of patients with polymyositis have antibodies to signal recognition particles (SRPs), which are associated with acute onset of severe weakness, increased incidence of cardiac involvement, and higher mortality rates.
- Perform age-appropriate evaluation for malignancy.
Imaging Studies
- Muscle-imaging techniques such as MRI and ultrasonography may be useful to document and localize the extent of muscle involvement (see Image 1).
MRI of thighs showing increased signal in the quadriceps muscles bilaterally consistent with inflammatory myositis.
- Chest radiography and high-resolution CT scanning of the chest are helpful for evaluation of interstitial lung disease.
- Barium swallow studies are helpful for evaluation of dysphagia or dysphonia.
Other Tests
- EMG findings are abnormal in almost all patients (90%) with polymyositis. Various abnormalities consistent with polymyositis may be found, depending on the stage of disease. In patients with inclusion body myositis, both myopathic and neuropathic changes may be present.
- Evidence of membrane irritability, increased insertional activity, fibrillation potentials, positive sharp waves at rest
- Myopathic changes of motor unit action potential, decreased amplitude and duration, increased polyphasic potentials, bizarre high-frequency repetitive discharges
- Chronic changes, evidence of denervation-reinnervation
- Pulmonary function tests and diffusion capacity for evaluation of interstitial lung disease may be appropriate.
Procedures
- Muscle biopsy is crucial in helping diagnose polymyositis and in excluding other rare muscle diseases. MRI can be used to guide the site of biopsy. Avoid biopsy of sites recently studied by EMG by using the contralateral side.
Histologic Findings
Muscle biopsy shows muscle fibers in varying stages of inflammation, necrosis, and regeneration (see Images 2-3). Findings include focal endomysial infiltration by mononuclear cells (consisting of mostly CD8+ T lymphocytes and macrophages), capillary obliteration, endothelial cell damage, and increased amounts of connective tissue. Later in the course of polymyositis, muscle-cell degeneration, fibrosis, and regeneration may be observed. Inclusion body myositis is histologically similar to polymyositis with the additional presence of intracytoplasmic inclusion bodies observed on electron microscopy. Dermatomyositis shows inflammatory changes, predominantly in the perimysial and perivascular regions with CD4+ T and B lymphocytes. Corticosteroid-induced myopathy causes no inflammatory changes. Type II fiber atrophy is the characteristic feature.
Histopathology of polymyositis showing endomysial mononuclear inflammatory infiltrate and muscle fiber necrosis.
Close view of muscle biopsy, showing chronic inflammatory infiltrate consisting of T lymphocytes, especially CD8+ T lymphocytes.
More on Polymyositis |
| Overview: Polymyositis |
 Differential Diagnoses & Workup: Polymyositis |
| Treatment & Medication: Polymyositis |
| Follow-up: Polymyositis |
| Multimedia: Polymyositis |
| References |
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References
Bohan A. History and classification of polymyositis and dermatomyositis. Clin Dermatol. Apr-Jun 1988;6(2):3-8. [Medline].
Schnabel A, Hellmich B, Gross WL. Interstitial lung disease in polymyositis and dermatomyositis. Curr Rheumatol Rep. Apr 2005;7(2):99-105. [Medline].
Cherin P, Pelletier S, Teixeira A, et al. Results and long-term followup of intravenous immunoglobulin infusions in chronic, refractory polymyositis: an open study with thirty-five adult patients. Arthritis Rheum. Feb 2002;46(2):467-74. [Medline].
Kumar A, Teuber SS, Gershwin ME. Intravenous immunoglobulin: striving for appropriate use. Int Arch Allergy Immunol. 2006;140(3):185-98. [Medline].
Hengstman G, Van den Housen F, Van Engelen B. Anti-TNF-blockade with infliximab (Remicade) in polymyositis and dermatomyositis. Arthritis and Rheumatology. 2000;43(9):S193.
Levine TD. Rituximab in the treatment of dermatomyositis: an open-label pilot study. Arthritis Rheum. Feb 2005;52(2):601-7. [Medline].
Alexanderson H. Exercise: an important component of treatment in the idiopathic inflammatory myopathies. Curr Rheumatol Rep. Apr 2005;7(2):115-24. [Medline].
Adams EM, Plotz PH. The treatment of myositis. How to approach resistant disease. Rheum Dis Clin North Am. Feb 1995;21(1):179-202. [Medline].
Aleksza M, Szegedi A, Antal-Szalmás P, Irinyi B, Gergely L, Ponyi A, et al. Altered cytokine expression of peripheral blood lymphocytes in polymyositis and dermatomyositis. Ann Rheum Dis. Oct 2005;64(10):1485-9. [Medline].
Amato AA, Barohn RJ. Idiopathic inflammatory myopathies. Neurol Clin. Aug 1997;15(3):615-48. [Medline].
Bohan A, Peter JB. Polymyositis and dermatomyositis (first of two parts). N Engl J Med. Feb 13 1975;292(7):344-7. [Medline].
Bohan A, Peter JB. Polymyositis and dermatomyositis (second of two parts). N Engl J Med. Feb 20 1975;292(8):403-7. [Medline].
Briani C, Doria A, Sarzi-Puttini P, et al. Update on idiopathic inflammatory myopathies. Autoimmunity. May 2006;39(3):161-70. [Medline].
[Best Evidence] Choy EH, Hoogendijk JE, Lecky B, et al. Immunosuppressant and immunomodulatory treatment for dermatomyositis and polymyositis. Cochrane Database Syst Rev. Jul 20 2005;CD003643. [Medline].
Dalakas MC. Polymyositis, dermatomyositis and inclusion-body myositis. N Engl J Med. Nov 21 1991;325(21):1487-98. [Medline].
Hicks JE. Rehabilitating patients with idiopathic inflammatory myopathy. Musculoskel Med. 1995;12:4-54.
Hill CL, Zhang Y, Sigurgeirsson B, et al. Frequency of specific cancer types in dermatomyositis and polymyositis: a population-based study. Lancet. Jan 13 2001;357(9250):96-100. [Medline].
Marie I, Hachulla E, Cherin P, et al. Opportunistic infections in polymyositis and dermatomyositis. Arthritis Rheum. Apr 15 2005;53(2):155-65. [Medline].
O'Rourke KS. Myopathies in the elderly. Rheum Dis Clin North Am. Aug 2000;26(3):647-72, viii. [Medline].
Oddis CV. Idiopathic inflammatory myopathies: a treatment update. Curr Rheumatol Rep. Dec 2003;5(6):431-6. [Medline].
Plotz PH, Miller F, Hoffman E, et al. Workshop on inflammatory myopathy Bethesda, 5-6 April 2000. Neuromuscul Disord. Jan 2001;11(1):93-5. [Medline].
Plotz PH, Rider LG, Targoff IN, et al. NIH conference. Myositis: immunologic contributions to understanding cause, pathogenesis, and therapy. Ann Intern Med. May 1 1995;122(9):715-24. [Medline].
Reimers CD, Finkenstaedt M. Muscle imaging in inflammatory myopathies. Curr Opin Rheumatol. Nov 1997;9(6):475-85. [Medline].
Salomonsson S, Lundberg IE. Cytokines in idiopathic inflammatory myopathies. Autoimmunity. May 2006;39(3):177-90. [Medline].
Spiera R, Kagen L. Extramuscular manifestations in idiopathic inflammatory myopathies. Curr Opin Rheumatol. Nov 1998;10(6):556-61. [Medline].
Targoff IN. Update on myositis-specific and myositis-associated autoantibodies. Curr Opin Rheumatol. Nov 2000;12(6):475-81. [Medline].
Henes JC, Heinzelmann F, Wacker A, Seelig HP, Klein R, Bornemann A, et al. Antisignal recognition particle-positive polymyositis successfully treated with myeloablative autologous stem cell transplantation. Ann Rheum Dis. Mar 2009;68(3):447-8. [Medline].
Further Reading
Keywords
polymyositis, PM, primary idiopathic polymyositis, idiopathic inflammatory myopathy, dermatomyositis, DM, inclusion body myositis, IBM, virus-mediated muscle injury, microvascular insult, collagen vascular disease
