eMedicine Specialties > Emergency Medicine > Allergy & Immunology

Polymyositis

Henry Rosenkranz, MD, Assistant Professor, Department of Emergency Medicine, Tufts University, New England Medical Center

Updated: Aug 25, 2009

Introduction

Background

Polymyositis (PM), dermatomyositis (DM), and inclusion body myositis (IBM) are the major members of a group of skeletal muscle diseases called the idiopathic inflammatory myopathies. Clinical features, characteristic muscle biopsy findings, immune markers, and histopathologic findings differentiate these illnesses. No strictly defined diagnostic criteria for polymyositis or dermatomyositis exist; however, Bohan and Peter proposed the criteria most widely cited. These criteria include the typical rash of dermatomyositis, findings at history and physical examination that reveal symmetric proximal muscular weakness, elevated serum muscle enzyme levels, electromyographic evidence of myopathic abnormalities, and characteristic findings at muscle biopsy.

Histopathology of polymyositis showing endomysial mononuclear inflammatory infiltrate and muscle fiber necrosis.

Polymyositis and dermatomyositis have many shared clinical features. Both are inflammatory myopathies that present as symmetric muscle weakness that develops over weeks to months. Initial treatment with corticosteroids usually produces a response; however, nonresponders require further treatment. Both conditions may be associated with malignancies. Despite these similarities, muscle biopsy findings and characteristic skin findings of dermatomyositis reveal each as a distinct clinical entity.

Although classified as an inflammatory myopathy, inclusion body myositis shows minimal evidence of inflammation. This is the most common inflammatory myopathy in patients older than 50 years. It presents as an asymmetric, distal weakness and also has distinct biopsy findings. Studies so far have not yielded significant response to treatment. Inclusion body myositis is not be discussed further in this article.

Pathophysiology

In both polymyositis and dermatomyositis, immune-mediated muscle inflammation and vascular damage occur. In polymyositis, the immune system is primed to act against previously unrecognized muscle antigens. In dermatomyositis, complement-mediated damage to endomysial vessels and microvasculature of the dermis occurs.

Frequency

United States

Overall, the annual incidence of inflammatory myopathy is 1 case per 100,000 persons per year.

Mortality/Morbidity

• The 5-year mortality rate is 20%.
• Mortality is most often related to associated malignancy or pulmonary complications; however, elderly patients with cardiac involvement or dysphagia also have a higher mortality rate.
• Outcome of treatment varies widely and is related to clinical and histologic features.

Race

Polymyositis and dermatomyositis are more common among blacks. Estimated black-to-white incidence for polymyositis is 5:1 and for dermatomyositis is 3:1.

Sex

Both polymyositis and dermatomyositis are more common in females, with an approximate 2:1 ratio.

Age

• Polymyositis is a disease of adults, and it is rare in persons younger than 20 years.
• Although dermatomyositis is primarily a disease of adults, it also is observed in children, usually those aged 5-14 years.

Clinical

History

The history of patients with polymyositis (PM) or dermatomyositis (DM) typically includes the following:

• Symmetric proximal muscle weakness with insidious onset
• Muscles usually painless (Myalgias occur in fewer than 30% of patients.)
• Dysphagia (30%) and aspiration, if pharyngeal and esophageal muscles are involved
• Arthralgias may be associated
• Difficulty kneeling, climbing or descending stairs, raising arms, and arising from a seated position; weak neck extensors cause difficulty holding the head up; involvement of pelvic girdle usually greater than upper body weakness
• Characteristic rash of face, trunk, and hands seen in DM only
• Family history and medication history are important in excluding other causes of myopathy.

Physical

Findings at physical examination may include the following:

• Muscle tenderness on palpation
• Normal sensory test results and reflexes (Reflexes may be abnormal with advanced disease.)
• Muscle atrophy
• In dermatomyositis (DM), a characteristic heliotrope rash preceding or accompanying muscle weakness
  • The heliotrope rash is a symmetric, confluent, purple-red, macular eruption of the eyelids and periorbital tissue. Edema may also be present.
  • Other rashes seen with DM include erythematous nail beds and a scaly, purple erythematous papular eruption over the dorsal metacarpophalangeal and interphalangeal joints (Gottron sign).
  • Violaceous erythematous confluent macular eruption over the deltoids, posterior part of the shoulders, and the neck is known as the shawl sign. A similar eruption of the V area of the anterior part of the neck and the upper part of the chest is known as the V sign.
• Extramuscular manifestations
  • Cardiac - Congestive heart failure (CHF), arrhythmia
  • Lung - Interstitial lung disease, pneumonia/aspiration
  • Gastrointestinal - Dysphagia
  • Joints - Arthralgias, symmetric arthritis

Causes

The specific etiology of polymyositis is unknown but is thought to be autoimmune.

• Muscle inflammation is immune mediated.
• Various hypotheses exist; some believe that a viral trigger causes autoimmune injury or that illness may reflect a paraneoplastic syndrome.

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.

Treatment

Emergency Department Care

• Generally, polymyositis is insidious and has a gradual progression.
• Acute treatment requires an awareness of polymyositis so that appropriate studies such as analyses of creatine kinase levels, aldolase levels, and erythrocyte sedimentation rates are performed.
• Complications, such as aspiration pneumonia, may be the presenting illness.

Consultations

• A neurologist or rheumatologist is the primary consultant.
• These disorders also often require the involvement of a dermatologist and internist. 

Medication

Therapy is based on immune suppression with steroids. If this is not successful, other immunosuppressive agents are used. Steroids are started at a high dose,¹ and tapering begins at 1-3 months, depending on the clinical response.

Corticosteroids

These agents have anti-inflammatory properties and may cause profound and varied metabolic effects. In addition, these agents modify the body's immune response to diverse stimuli.

Prednisone (Deltasone, Orasone, Meticorten)

Useful in the treatment of inflammatory and allergic reactions. May decrease inflammation by reversing increased capillary permeability and suppressing PMN activity.

Dosing

Adult

0.05-2 mg/kg PO divided bid/qid; taper over 2 wk as symptoms resolve

Pediatric

4-5 mg/m²/d PO; taper over 2 wk as symptoms resolve

Interactions

Coadministration with estrogens may decrease prednisone clearance; concurrent use with digoxin may cause digitalis toxicity secondary to hypokalemia; phenobarbital, phenytoin, and rifampin may increase metabolism of glucocorticoids (consider increasing maintenance dose); monitor for hypokalemia with coadministration of diuretics

Contraindications

Documented hypersensitivity; viral infection, peptic ulcer disease, hepatic dysfunction, connective tissue infections, and fungal or tubercular skin infections; GI disease

Precautions

Pregnancy

B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals

Precautions

Abrupt discontinuation of glucocorticoids may cause adrenal crisis; hyperglycemia, edema, osteonecrosis, myopathy, peptic ulcer disease, hypokalemia, osteoporosis, euphoria, psychosis, myasthenia gravis, growth suppression, and infections may occur with glucocorticoid use

Immunosuppressants

These agents are useful in the treatment of autoimmune disease.

Azathioprine (Imuran)

Antagonizes purine metabolism and inhibits synthesis of DNA, RNA, and proteins. May decrease proliferation of immune cells, which results in lower autoimmune activity. Second-line agent occasionally used with steroids to allow a lower steroid dose. Also used if relapse of disease occurs during tapering of steroids. Treatment for 6 mo may be required.

Dosing

Adult

Starting dose: 2-5 mg/kg/d PO
Maintenance dose: 1-2 mg/kg/d PO

Pediatric

Administer as in adults

Interactions

Toxicity increases with allopurinol; concurrent use with ACE inhibitors may induce severe leukopenia; may increase levels of methotrexate metabolites and decrease effects of anticoagulants, neuromuscular blockers, and cyclosporine

Contraindications

Documented hypersensitivity

Precautions

Pregnancy

D - Fetal risk shown in humans; use only if benefits outweigh risk to fetus

Precautions

Increases risk of neoplasia; caution with liver disease and renal impairment; hematologic toxicities may occur

Methotrexate (Folex)

The mechanism of action of methotrexate in the treatment of inflammatory reactions is unknown. It may affect immune function and usually ameliorates the symptoms of inflammation (eg, pain, swelling, stiffness). Second-line agent when no response to prednisone occurs.

Dosing

Adult

7.5 mg PO initially; increase by 2.5 mg/wk to a total of 20 mg/wk

Pediatric

5-15 mg/m²/wk PO/IM single dose or divided tid with doses 12 h apart

Interactions

Oral aminoglycosides may decrease absorption and blood levels of concurrent oral methotrexate; charcoal lowers levels; coadministration with etretinate may increase hepatotoxicity of methotrexate; folic acid or its derivatives contained in some vitamins may decrease response; coadministration with NSAIDs may elevate methotrexate levels and can be fatal, used with caution when taking high dose methotrexate; may decrease phenytoin serum levels; probenecid, procarbazine, and sulfonamides, including TMP-SMZ, may increase effects and toxicity; may increase plasma levels of thiopurines

Contraindications

Documented hypersensitivity; alcoholism, hepatic insufficiency, documented immunodeficiency syndromes, preexisting blood dyscrasias (eg, bone marrow hypoplasia, leukopenia, thrombocytopenia, significant anemia)

Precautions

Pregnancy

D - Fetal risk shown in humans; use only if benefits outweigh risk to fetus

Precautions

Has particularly toxic effects on bone marrow, liver, lungs, and kidneys; monitor CBCs monthly and liver and renal function q1-3mo during therapy (monitor more frequently during initial dosing, dose adjustments, or with risk of elevated level, such as with dehydration); discontinue if significant drop in blood count occurs; aspirin, NSAIDs, or low-dose steroids may be administered concomitantly with caution

Immunoglobulins

These agents are used to neutralize antibodies that may be associated with autoimmune diseases.

Intravenous immunoglobulin (Gamimune, Gammagard)

Neutralize circulating myelin antibodies through anti-idiotypic antibodies; down-regulates proinflammatory cytokines, including INF-gamma; blocks Fc receptors on macrophages; suppresses inducer T and B cells and augments suppressor T cells; blocks complement cascade; promotes remyelination; may increase CSF IgG (10%). IVIG has been used for treatment in patients who have refractory disease. Reports about its effectiveness conflict.

Dosing

Adult

2 g/kg/d IV slowly for 3-5 d; repeat at monthly intervals

Pediatric

Administer as in adults

Interactions

Increases toxicity of live virus vaccine (MMR); do not administer within 3 mo of vaccine

Contraindications

Documented hypersensitivity; IgA deficiency; anti-IgE/IgG antibodies

Precautions

Pregnancy

C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus

Precautions

Check serum IgA level before use (use an IgA-depleted product, eg, Gammagard S/D); infusions may increase serum viscosity and thromboembolic events; infusions may increase risk of migraine attacks, aseptic meningitis (10%), urticaria, pruritus, or petechiae (2-30 d after infusion); increases risk of renal tubular necrosis in elderly patients and in patients with diabetes, volume depletion, and preexisting kidney disease; lab result changes associated with infusions include elevated antiviral or antibacterial antibody titers for 1 mo, 6-fold increase in ESR for 2-3 wk, and apparent hyponatremia

Follow-up

Further Outpatient Care

• Physical therapy should begin early in the course of polymyositis to maintain mobility and strength.
• Findings from continuing clinical assessment and muscle enzyme abnormalities guide the duration of treatment.

Complications

• Pneumonia
• Infection
• Myocardial infarction
• Carcinoma (especially in the breast and lung)
• Severe dysphagia
• Interstitial lung disease
• Aspiration pneumonitis
• Steroid myopathy or other complications of steroid therapy

Prognosis

• Overall, the 5-year mortality rate for polymyositis (PM) and dermatomyositis (DM) is 20%.
• Significant morbidity is associated with these diseases, and medications used in treating them may also cause significant side effects.
• Death is closely related to presence of malignancy or respiratory/pulmonary involvement.²
• Residual weakness occurs in approximately 30% of patients.
• Persistent active disease is present in approximately 20% of patients.
• Survival is less likely in women and African American patients.
• Most patients improve with therapy.
• Full recovery is expected in 50% of patients.

Patient Education

• The Myositis Association of America Web site is an excellent resource for patients with inflammatory myopathies, their families, and the medical community.

Miscellaneous

Medicolegal Pitfalls

• Failure to consider an underlying malignancy when diagnosing DM or PM

Multimedia

Media file 1: MRI of thighs showing increased signal in the quadriceps muscles bilaterally consistent with inflammatory myositis.

Media file 2: Histopathology of polymyositis showing endomysial mononuclear inflammatory infiltrate and muscle fiber necrosis.

Media file 3: Hematoxylin and eosin frozen section shows polymyositis. Endomysial chronic inflammation is present among intact myofibers that are remarkable only for increased variability of fiber size. Image courtesy of Roberta J. Seidman, MD.

Media file 4: 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.

Media file 5: 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.

Media file 6: 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.

References

1. Hengstman GJ, van den Hoogen FH, van Engelen BG. Treatment of the inflammatory myopathies: update and practical recommendations. Expert Opin Pharmacother. May 2009;10(7):1183-90. [Medline].

2. Bronner IM, van der Meulen MF, de Visser M, Kalmijn S, van Venrooij WJ, Voskuyl AE. Long-term outcome in polymyositis and dermatomyositis. Ann Rheum Dis. Nov 2006;65(11):1456-61. [Medline].

3. Amato AA, Barohn RJ. Idiopathic inflammatory myopathies. Neurol Clin. Aug 1997;15(3):615-48. [Medline].

4. Chahin N, Engel AG. Correlation of muscle biopsy, clinical course, and outcome in PM and sporadic IBM. Neurology. Sep 26 2007;[Medline].

5. Christopher-Stine L, Plotz PH. Myositis: an update on pathogenesis. Curr Opin Rheumatol. Nov 2004;16(6):700-6. [Medline].

6. Dalakas MC, Hohlfeld R. Polymyositis and dermatomyositis. Lancet. Sep 20 2003;362(9388):971-82. [Medline].

7. Dalakas MC, Sivakumar K. The immunopathologic and inflammatory differences between dermatomyositis, polymyositis and sporadic inclusion body myositis. Curr Opin Neurol. Jun 1996;9(3):235-9. [Medline].

8. 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].

9. Koopman WJ. Polymyositis/dermatomyositis classification criteria. In: Arthritis and Allied Conditions. 1997:17-8.

10. Mastaglia FL, Ojeda VJ. Inflammatory myopathies: Part 1. Ann Neurol. Mar 1985;17(3):215-27. [Medline].

11. 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].

12. Olsen NJ, Park JH. Inflammatory myopathies: issues in diagnosis and management. Arthritis Care Res. Jun 1997;10(3):200-7. [Medline].

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

Contributor Information and Disclosures

Author

Henry Rosenkranz, MD, Assistant Professor, Department of Emergency Medicine, Tufts University, New England Medical Center
Henry Rosenkranz, MD is a member of the following medical societies: American Academy of Emergency Medicine and American College of Emergency Physicians
Disclosure: Nothing to disclose.

Medical Editor

Michael S Beeson, MD, MBA, FACEP, Professor of Emergency Medicine, Northeastern Ohio Universities College of Medicine; Program Director, Emergency Medicine Residency, Summa Health System
Michael S Beeson, MD, MBA, FACEP is a member of the following medical societies: American College of Emergency Physicians, Council of Emergency Medicine Residency Directors, National Association of EMS Physicians, and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: eMedicine Salary Employment

Managing Editor

Gino A Farina, MD, Program Director, Associate Professor of Clinical Emergency Medicine, Department of Emergency Medicine, Long Island Jewish Medical Center, Albert Einstein College of Medicine
Gino A Farina, MD is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.

CME Editor

John D Halamka, MD, MS, Associate Professor of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center; Chief Information Officer, CareGroup Healthcare System and Harvard Medical School; Attending Physician, Division of Emergency Medicine, Beth Israel Deaconess Medical Center
John D Halamka, MD, MS is a member of the following medical societies: American College of Emergency Physicians, American Medical Informatics Association, Phi Beta Kappa, and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.

Chief Editor

Robert E O'Connor, MD, MPH, Professor and Chair, Department of Emergency Medicine, University of Virginia Health System
Robert E O'Connor, MD, MPH is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, American College of Physician Executives, American Heart Association, American Medical Association, Medical Society of Delaware, National Association of EMS Physicians, Society for Academic Emergency Medicine, and Wilderness Medical Society
Disclosure: Nothing to disclose.

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