AUTHOR AND EDITOR INFORMATION

Section 1 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

INTRODUCTION

Section 2 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

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 PM or DM exist; however, Bohan and Peter proposed the criteria most widely cited. These criteria include the typical rash of DM, 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.

PM and DM 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 DM reveal each as a distinct clinical entity.

Although classified as an inflammatory myopathy, IBM 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. IBM will not be discussed further in this article.

Pathophysiology

In both PM and DM, immune-mediated muscle inflammation and vascular damage occur. In PM, the immune system is primed to act against previously unrecognized muscle antigens. In DM, 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

PM and DM are more common among blacks. Estimated black-to-white incidence for PM is 5:1 and for DM is 3:1.

Sex

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

Age

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

CLINICAL

Section 3 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

History

The history of patients with PM or 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 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 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.

DIFFERENTIALS

Section 4 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

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

Section 5 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Lab 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.
• 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.

TREATMENT

Section 6 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Emergency Department Care

• Generally, the disease is insidious and has a gradual progression.
• Acute treatment requires an awareness of PM 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

Section 7 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

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, and tapering begins at 1-3 months, depending on the clinical response.

Drug Category: 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.

Drug Category: Immunosuppressants

These agents are useful in the treatment of autoimmune disease.

Drug Name	Methotrexate (Folex)
Description	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.
Adult Dose	7.5 mg PO initially; increase by 2.5 mg/wk to a total of 20 mg/wk
Pediatric Dose	5-15 mg/m2/wk PO/IM single dose or divided tid with doses 12 h apart
Contraindications	Documented hypersensitivity; alcoholism, hepatic insufficiency, documented immunodeficiency syndromes, preexisting blood dyscrasias (eg, bone marrow hypoplasia, leukopenia, thrombocytopenia, significant anemia)
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
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

Drug Category: Immunoglobulins

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

FOLLOW-UP

Section 8 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Further Outpatient Care

• Physical therapy should begin early in the course of illness 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 PM and 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.
• 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

Section 9 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Medical/Legal Pitfalls

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

REFERENCES

Section 10 of 10

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

• Amato AA, Barohn RJ. Idiopathic inflammatory myopathies. Neurol Clin. Aug 1997;15(3):615-48. [Medline].
• 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].
• Chahin N, Engel AG. Correlation of muscle biopsy, clinical course, and outcome in PM and sporadic IBM. Neurology. Sep 26 2007;[Medline].
• Christopher-Stine L, Plotz PH. Myositis: an update on pathogenesis. Curr Opin Rheumatol. Nov 2004;16(6):700-6. [Medline].
• Dalakas MC, Hohlfeld R. Polymyositis and dermatomyositis. Lancet. Sep 20 2003;362(9388):971-82. [Medline].
• 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].
• 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.
• Mastaglia FL, Ojeda VJ. Inflammatory myopathies: Part 1. Ann Neurol. Mar 1985;17(3):215-27. [Medline].
• 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].
• Olsen NJ, Park JH. Inflammatory myopathies: issues in diagnosis and management. Arthritis Care Res. Jun 1997;10(3):200-7. [Medline].

Article Last Updated: Nov 28, 2007