AUTHOR AND EDITOR INFORMATION

Section 1 of 11  

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

INTRODUCTION

Section 2 of 11  

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

Background

In 1863, Wagner first recognized dermatomyositis/polymyositis. In 1891, Unverricht provided the first description of dermatomyositis. Dermatomyositis and polymyositis have been classified into the following clinical groups, as Walton and Adams originally proposed:

• Primary polymyositis (idiopathic, adult)
• Dermatomyositis (idiopathic, adult)
• Childhood dermatomyositis or myositis with necrotizing vasculitis
• Polymyositis associated with connective tissue disorder (ie, overlap syndrome)
• Polymyositis or dermatomyositis associated with neoplasia

Inflammatory myopathies are acquired muscle diseases characterized by primary muscle weakness, endomysial inflammation, and elevated levels of serum muscle enzymes. Polymyositis and dermatomyositis, along with inclusion-body myositis, are the most common diseases of the striated muscle, skin, and surrounding connective tissue that clinicians observe. Each has unique clinical and histologic features. The pathology of both polymyositis and dermatomyositis have an underlying autoimmune basis, but the mechanisms for the 2 conditions differ.

Pathophysiology

Polymyositis

Polymyositis is presumed to be an autoimmune-mediated disease secondary to defective cellular immunity, which may be due to diverse causes that may occur alone or in association with viral infections, malignancies, or connective-tissue disorders. Evidence suggests that a T cell–mediated cytotoxic process is directed against unidentified muscle antigens. Supporting this conclusion are CD8 T cells, which, along with macrophages, initially surround healthy nonnecrotic muscle fibers and eventually invade and destroy them.

The factors triggering a T cell–mediated process in polymyositis are unclear. Viruses have been implicated; however, so far, only the human retroviruses HIV and human T-cell lymphotrophic virus type I (HTLV-I), the simian retroviruses, and coxsackievirus B have been etiologically connected with the disease. These viruses may directly invade the muscle tissue, damaging the vascular endothelium and releasing cytokines, which then induce abnormal expression of the major histocompatibility complex (MHC) and which render the muscle susceptible to destruction.

An autoimmune response to nuclear and cytoplasmic autoantigens is detected in about 60-80% of patients with polymyositis and dermatomyositis. Some serum autoantibodies are shared with other autoimmune diseases (ie, myositis-associated antibodies [MAA]), and some are unique to myositis (ie, myositis-specific antibodies [MSA]). The MSA are found in approximately 40% of patients with polymyositis and dermatomyositis, whereas MAA are found in 20-50%.

Myositis-specific antibodies

The identified MSA targets include 3 distinct groups of proteins: aminoacyl–transfer RNA (tRNA) synthetases (anti-Jo-1), nuclear Mi-2 protein, and components of the signal-recognition particle (SRP).

Most of the anti-tRNA synthetase antibodies are directed toward functional and highly conserved domains of the enzyme. As many as 6 of 20 aminoacyl-tRNA synthetases have been described, but anti-histidyl-tRNA synthetase (Jo-1) is most common (20-30%). Autoantibodies directed toward the other synthetases specific for alanine (anti-PL12), glycine (anti-EJ), isoleucine (anti-OJ), threonine (anti-PL7), and asparagine (anti-KS) have been reported in only about 1% of patients. Anti-Jo-1 autoantibodies were originally described as precipitating autoantibodies in sera of patients with polymyositis. Later, the anti-Jo-1 antibodies were recognized to be specific for patients with polymyositis. The target for the anti-Jo-1 antibodies was one of a family of distinct cellular enzymes: the aminoacyl-tRNA synthetases.

The Jo-1 antigen is histidyl-tRNA synthetase. This enzyme is partially responsible for attaching tRNA to their cognate ribosomal RNA (rRNA). The Jo-1 antigen migrates as a 53-kd protein on sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE).

The presence of autoantibodies against the Jo-1 antigen has been reported in up to 23% of polymyositis patients by immunodiffusion. Anti–Jo-1 antibodies are almost completely specific for myositis and are more common in polymyositis than in dermatomyositis and rare in children. The presence of anti-Jo-1 antibodies defines a distinct group of polymyositis patients with interstitial lung disease, arthritis, and fevers. The anti–Jo-1 response appears to be self-antigen driven, having a broad spectrotype over time and undergoing isotype switching. Anti–Jo-1 antibodies also inhibit the function of histidyl-tRNA synthetase in humans more than they do in other species.

Anti-Mi-2 antibodies recognize a major protein of a nuclear complex formed by at least 7 proteins that is involved in the transcription process. Autoantibodies recognizing Mi-2 are considered specific serologic markers of dermatomyositis. They are detected in about 20% of patients with myositis and are associated with relatively acute onset, a good prognosis, and a good response to therapy.

Anti-SRP antibodies are directed towards an RNA-protein complex that consists of 6 proteins and a 300-nucleotide RNA molecule (7SL RNA). Patients with anti-SRP antibodies have acute polymyositis with cardiac involvement, a poor prognosis, and a poor response to therapy.

Myositis-associated antibodies

The MAA are found in the sera of 20-50% of patients and are commonly encountered in other connective tissue diseases. The most important antigenic targets of the MAA are the PM/Scl nucleolar antigen, the nuclear Ku antigen, the small nuclear ribonucleoproteins (snRNP), and the cytoplasmic ribonucleoproteins (RoRNP). The anti-PM/Scl autoantibodies are generally found in patients affected by polymyositis overlapping with scleroderma. Anti-Ku antibodies are found in patients with myositis overlapping with other connective tissue diseases. Antibodies directed against snRNP are frequently found in patients with myositis and in patients with connective tissue–disease overlap syndrome, whereas antibodies toward Ro/SSA 60 kd, Ro/SSA 52 kd, and La/SSB protein components of the RoRNP complex are almost exclusively found in patients with Sjögren syndrome and systemic lupus erythematosus (SLE).

Dermatomyositis

Dermatomyositis is likely the result of a humoral attack on the muscle capillaries and small arterioles. Complement c5b-9 membrane-attack complex is deposited and is needed in preparing the cell for destruction in antibody-mediated disease. B cells and CD4 (helper) cells are also present in abundance in the inflammatory reaction associated with the blood vessels. As the disease progresses, the capillaries are destroyed, and the muscles undergo microinfarction. Perifascicular atrophy occurs in the beginning; however, as the disease advances, necrotic and degenerative fibers are present throughout the muscle.

Frequency

International

The incidence of polymyositis and dermatomyositis is 5-10 cases per 100,000 individuals.

Mortality/Morbidity

The active period of the disease is approximately 2-3 years in both children and adults. The duration is greater for patients with cardiac or pulmonary complications than for others; approximately 20% of the patients recover completely. The mortality rate after several years of the disease is approximately 15%; the rate is increased in patients with dermatomyositis with connective tissue diseases and malignancy.

Race

No racial predilection is observed.

Sex

A female preponderance has been reported in all age groups, with a female-to-male ratio of 2:1.

Age

• Most patients present with polymyositis when aged 30-60 years, with a small peak in people aged 15 years.
• Dermatomyositis affects children and adults equally. The peak incidence is observed in individuals aged 45-64 years, with a small peak in children aged 5-14 years.

CLINICAL

Section 3 of 11  

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

History

• Polymyositis
• • Polymyositis is a disease of exclusion with acute or subacute onset. It is best defined as an inflammatory myopathy of subacute onset (ie, weeks to months) and steady progression occurring in adults who develop diffuse weakness, which is more severe proximally than distally.
  • The weakness is painless in two thirds of the patients. A rash is not present.
  • Eye muscles are not involved, and facial muscles are involved only with severe disease.
  • Family history of neuromuscular disease, endocrinopathy, or exposure to myotoxic drugs or toxins is absent.
  • The disease may exist for several months before the patient seeks medical advice, and all the muscles of the thighs, trunk, shoulders, hips, and upper arms are usually involved.
  • Symptoms include difficulty getting up from a chair, climbing steps, stepping onto a curb, lifting objects, and combing hair. Fatigue, myalgias, and muscle cramps may also be present.
  • In contrast, fine motor movements that depend on the strength of distal muscles, such as buttoning a shirt, sewing, knitting, or writing are affected only late in the disease.
• Dermatomyositis
• • Dermatomyositis occurs in children as well as adults. It is characterized by the muscle weakness.
  • Extramuscular manifestations of the disease may include the following:
    • General systemic disturbances, fever, arthralgia, malaise, weight loss, Raynaud phenomenon
    • Dysphagia, similar to that of scleroderma
    • Atrioventricular defects, tachyarrhythmias, dilated cardiomyopathies
    • Gastrointestinal (GI) ulcers and infections
    • Contracture of joints
    • Pulmonary involvement due to weakness of thoracic muscles, interstitial lung disease
    • Subcutaneous calcifications
  • Dermatomyositis in children resembles the adult form. Children commonly develop a tiptoe gait secondary to flexion contracture of the ankles in early childhood.
  • Children tend to have extramuscular manifestations, especially GI ulcers and infections, more frequently than adults do.

Physical

• Polymyositis
• • Nothing is characteristic about the muscle weakness. It is not painful, although a minority of patients report aches or cramps.
  • The weakness may fluctuate from week to week and from month to month.
  • Ocular muscles remain normal even in advanced untreated cases.
  • Facial muscles remain normal except in rare advanced cases.
  • The pharyngeal and neck flexor muscles are often involved, causing dysphagia and difficulty in holding up the head.
  • In advanced cases and rarely in acute cases, respiratory muscles are affected. Severe weakness is almost always associated with muscular wasting.
  • Sensation remains normal.
  • On occasion, the muscle may be sore to palpation and may have a nodular and grainy feel.
  • The tendon reflexes are preserved, but they may be absent in severely weakened or atrophied muscles.
  • Primary cardiac abnormalities due to myocarditis may be present in a few patients. These abnormalities mainly manifest as atrioventricular conduction defects, tachyarrhythmias, low ejection fraction, dilated cardiomyopathy, or congestive heart failure.
  • General systemic disturbances, such as fever, malaise, weight loss, arthralgia, and Raynaud phenomenon, may occur when polymyositis is associated with a connective-tissue disorder.
• Dermatomyositis
• • The rash consists of a heliotrope (ie, blue-purple) discoloration on the upper eyelids; a flat, red rash involving the face and upper trunk; and a raised, violaceous, scaly eruption on the knuckles (ie, Gottron rash).
  • The erythematous lesions may result in scaling, pigmentation, and depigmentation of the skin, producing a shiny appearance.
  • The rash may involve other body surfaces, including knees, elbows, neck, anterior chest (ie, V sign), or back and shoulders (ie, shawl sign); sun exposure can exacerbate the rash.
  • Dilated capillary loops at the base of the fingernail are characteristic of dermatomyositis. The cuticles may be irregular and thickened, and the palmar and lateral surfaces of the fingers may become rough and cracked.
  • Myopathy in dermatomyositis is more proximal than distal.
  • The degree of weakness may range from mild to moderate to severe. Sometimes, quadriparesis are observed.
  • Muscle pain and tenderness are observed early in the course of the disease.
  • Sensation is normal, and tendon reflexes are preserved unless the muscle is severely weak and atrophic.

Causes

The causes of idiopathic polymyositis and dermatomyositis are not known. An autoimmune process is implicated (as discussed above) because these conditions may be associated with other autoimmune diseases, such as myasthenia gravis, Hashimoto thyroiditis, scleroderma, Waldenström macroglobulinemia, and others and because they respond to immunosuppressive medication.

DIFFERENTIALS

Section 4 of 11  

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

Other Problems to be Considered

Polymyositis is a diagnosis of exclusion.

Groups of diseases that should be excluded

Familial neuromuscular diseases
Systemic metabolic muscle diseases, eg, endocrinopathies and mitochondriopathies
Systemic medical illness, eg, malabsorption syndromes, alcoholism, cancer, vasculitis, granulomatous disease, sarcoidosis, or treatment with various known myotoxic drugs or toxins
Biochemical muscle diseases (eg, enzyme deficiencies)
Inclusion-body myositis (excluded by histologic findings)

Diseases differentiated by skin changes

The rash and subcutaneous calcifications are so characteristic of dermatomyositis that the diagnosis of dermatomyositis is very rarely in doubt. Some of the diseases from which it must be differentiated on the basis of skin changes are as follows:

SLE: The skin changes in the phalanges must be distinguished from dermatomyositis because, in SLE, the phalanges are involved and the knuckles are spared; in dermatomyositis, the reverse is true.

Eosinophilia myalgia syndrome: This was caused by the ingestion of contaminated L-tryptophan and has not been observed since the contaminated product was identified. The skin can be tight and shiny, but it is not erythematous. Joint contractures are common. Although the inflammatory process is confined mostly to the subcutaneous tissue, inflammation can spread to the muscle and cause myopathic muscle weakness.

Shulman syndrome (eosinophilic fasciitis): Patients with this syndrome present with joint contractures and thickening of the skin and subcutaneous tissue.

Other conditions

Other conditions that must be kept in mind when considering polymyositis and dermatomyositis are as follows:

Overlap syndromes: Polymyositis and, less commonly, dermatomyositis can be associated with other collagen-vascular diseases (ie, overlap syndromes). SLE, systemic sclerosis, rheumatoid arthritis, and Sjögren syndrome all may have weakness as a facet of the disease complex. Muscular weakness and atrophy are greater than what arthritis alone can account for. They are characterized by elevated titers of anti–U1/U2-ribonucleoprotein antibodies, PM-Scl antibodies or SSA antibodies in scleroderma, Sjögren syndrome, SLE, or mixed connective tissue disease. Dermatomyositis is rarely associated with other collagen-vascular diseases except for scleroderma.

Carcinoma with polymyositis or dermatomyositis: Polymyositis and especially dermatomyositis may be a part of paraneoplastic syndromes. About 10-20% of patients with dermatomyositis have neoplasms. In elderly patients with dermatomyositis, associated neoplasm is frequently found. Cancers of breast, lung, ovary, and stomach are most commonly implicated.

WORKUP

Section 5 of 11  

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

Lab Studies

• Polymyositis
• • The diagnosis of polymyositis is established by using serum enzyme levels and electromyography (EMG) studies and confirmed by means of diagnostic muscle biopsy.
  • The most sensitive enzyme is creatine kinase (CK). In the presence of disease, levels can be elevated as much as 50 times the reference level. The CK level usually parallels disease activity. In active polymyositis, it is rarely in the reference range. The level may also be in the reference range in some patients with polymyositis associated with connective-tissue disease.
  • Anti-Jo-1 antibodies are present in one fifth of patients.
  • Along with CK, levels of aldolase, serum aspartate aminotransferase (AST, or glutamic-oxaloacetic transaminase [SGOT]), serum alanine aminotransferase (ALT, or glutamic-pyruvic transaminase [SGPT]), and lactate dehydrogenase (LDH) may also be elevated. If AST levels are higher than ALT levels, a myogenic cause should be suspected.
• Dermatomyositis
• • Levels of serum CK are usually, though not always, elevated. Levels may be as high as several 100s to 1000 U/mL.
  • AST, ALT, LDH, and aldolase levels may also be elevated.
  • Cancer antigen 125 (CA125) and cancer antigen 19-9 (CA19-9) may be useful markers of the risk of tumors in patients with dermatomyositis and polymyositis. Therefore, tests of these markers should be included in the search for cancer in patients with dermatomyositis/polymyositis, especially those without interstitial lung disease

Imaging Studies

• MRI may show increased signal intensity in the affected muscles and surrounding tissues.
• Because of the lack of sensitivity and specificity, MRI is not helpful in diagnosing the disease; however, it can help in monitoring its progress, and it may be used to guide decisions regarding muscle biopsy.

Procedures

• EMG may be helpful in diagnosis, though findings can be normal in 15% of patients. It shows a typical myopathic pattern with irritability, although it is not specific for the condition. These findings are most consistently observed in weak proximal muscles. EMG also is helpful in selecting a muscle for biopsy.
• Specific findings are as follows:
• • In polymyositis, needle EMG shows myopathic potentials characterized by short-duration, low-amplitude polyphasic units on voluntary activation and increased spontaneous activity with fibrillations, complex and repetitive discharges, and positive and sharp waves, along with early recruitment.
  • In dermatomyositis, needle EMG shows myopathic features with indications of muscle irritability. The myopathic potentials are characterized by short-duration, low-amplitude, polyphasic units and increased spontaneous activity with fibrillations, complex repetitive discharges, and positive sharp waves. Recruitment pattern shows early recruitment.
• Single-fiber EMG (SFEMG)
• • In 1 study, SFEMG were recorded from the extensor digitorum communis of 34 patients with polymyositis or dermatomyositis and compared with findings on routine EMG, serum CK determination, and muscle biopsy.
  • SFEMG recordings were abnormal in all 34 patients. The prominent feature was markedly increased fiber density with normally or mildly increased jitter.
  • SFEMG is of great value in diagnosis and in evaluating the disease process to understand inflammatory myopathies in patients with clinically suspected disease but normal findings on routine EMG, CK determination, and muscle biopsy.

Histologic Findings

Polymyositis

Muscle biopsy is the definitive test not only for establishing the diagnosis of polymyositis but also for excluding other neuromuscular diseases. In polymyositis, inflammation is the histologic hallmark of the disease. The endomysial infiltrates are mostly in foci in the fascicles, initially surrounding healthy muscle fibers and finally invading these cells and resulting in phagocytosis and necrosis. Because the inflammatory infiltrates can be small and multifocal, they can be missed in a small muscle-biopsy specimen. Perifascicular atrophy or prominent perivascular infiltrates are not present, and the blood vessels are normal. When the disease becomes chronic, the connective tissue increases. The diagnosis of polymyositis is definite when a patient has subacute elevated levels of serum CK and findings on muscle biopsy consistent with the histologic features of polymyositis (see Images 1-4).

Dermatomyositis

Findings on muscle biopsy can be diagnostic. Although inflammation is the histologic hallmark of dermatomyositis, polymyositis, and inclusion-body myositis, dermatomyositis is the only disease that shows perifascicular atrophy. In addition, many fibers undergo degeneration and necrosis that cause them to lose their staining ability; therefore, they are termed ghost fibers. When these changes are associated with collections of inflammatory cells around the blood vessels, the diagnosis of dermatomyositis is certain (see Images 5-7).

TREATMENT

Section 6 of 11  

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

Medical Care

The goal of therapy is to improve muscle strength to improve function in activities of daily living. Improvement in strength is usually accompanied by a decrease in the serum CK level, a change that must be interpreted with caution because most immunosuppressive therapies decrease levels of serum muscle enzymes without necessarily improving muscle strength.

Consultations

• Consultation with an occupational and rehabilitation therapist may help patients with ambulation by providing necessary equipment.
• A swallowing evaluation for dysphagia is recommended.
• Proper emotional support is also important.

Diet

Advise patients who are receiving steroid therapy to follow a strict low-salt, low-carbohydrate, and high-protein diet to avoid weight gain and hypertension.

Activity

Physical therapy helps to preserve muscle function and prevents disuse atrophy of the weak muscles or joint contractures; therefore, consider it in the initial stage of the disease.

MEDICATION

Section 7 of 11  

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

Of all the treatments that are available, prednisone remains the drug of choice. If treatment with steroids is not successful, other lines of treatment are considered, such as intravenous immunoglobulins (IVIG), antineoplastic agents, and antimetabolites.

Drug Category: Systemic corticosteroids

Corticosteroids act as anti-inflammatory and immunosuppressive agents and are the first-line drug for treating both polymyositis and dermatomyositis.

Drug Category: Antineoplastic agents

These drugs inhibit cell growth and proliferation. Cyclophosphamide has shown promising results. The drug may be helpful in a subset of patients with interstitial lung disease. Methotrexate (MTX), an antagonist of folate metabolism, has been used frequently despite disappointing results.

Drug Name	Methotrexate (Folex PFS, Rheumatrex)
Description	Unknown mechanism of action in treatment of inflammatory reactions. Ameliorates symptoms of inflammation (eg, pain, swelling, stiffness). May affect immune function, including inhibition of production of proinflammatory cytokines. Adjust dose gradually to attain satisfactory response. Children who do not respond to high-dose prednisone should be treated with MTX immediately.
Adult Dose	7.5 mg/wk PO/SC as single dose qwk; depending on clinical response, increase dose 2.5-5 mg/wk to maximum of 25 mg/wk; may also administer IV
Pediatric Dose	Usually started with single weekly dose of 0.25 mg/kg/wk PO/SC, followed by weekly increase to maximum of 0.6 mg/kg/wk depending on clinical response or toxicity
Contraindications	Documented hypersensitivity; alcoholism; hepatic insufficiency; documented immunodeficiency syndromes; preexisting blood dyscrasias (eg, bone marrow hypoplasia, leukopenia, thrombocytopenia, clinically significant anemia); renal insufficiency
Interactions	Concurrent PO aminoglycosides may decrease absorption and blood levels; charcoal lowers levels; coadministration with etretinate may increase hepatotoxicity; folic acid or its derivatives contained in some vitamins may decrease response; probenecid, NSAIDs, salicylates, procarbazine, and sulfonamides, including TMP-SMZ, can increase plasma levels; may decrease phenytoin plasma levels; may increase plasma levels of thiopurines
Pregnancy	X - Contraindicated in pregnancy
Precautions	Monitor CBC counts qmo and liver and renal function q1-3mo during therapy (more frequently during initial dosing or dose adjustments or elevated MTX is a risk [eg, in dehydration]); toxic effects on hematologic, renal, GI, pulmonary, and neurologic systems; discontinue if blood counts decrease substantially; fatal reactions reported when administered concurrently with NSAIDs; adverse effects include MTX pneumonitis, stomatitis, GI symptoms, leukopenia, renal toxicity, and hepatotoxicity

Drug Category: Immunoglobulins

These drugs improve the clinical and immunologic aspects of the disease. May decrease autoantibody production and increase solubilization and removal of immune complexes. IVIG has been effective in dermatomyositis. Improvement is observed after the first infusion and is evident clearly by the second monthly infusion. If no improvement is observed by second or third dose, treatment is unlikely to be successful.

Drug Category: Immunosuppressant agents

The use of a nonsteroidal immunosuppressive drug is determined by the need for a steroid-sparing effect when (1) serious complications have developed with steroid use, (2) repeated relapses have occurred each time an attempt was made to lower a high steroid dosage, (3) prednisone did not improve strength, or (4) the patient has a rapidly progressive disease accompanied by severe weakness and respiratory failure.

Drug Name	Azathioprine (Imuran)
Description	Increasingly popular alternative to corticosteroids. Derivative of 6-mercaptopurine. Dosages of 1.5-2 mg/kg/d PO well tolerated. Adverse effects fewer than those of other immunosuppressive agents.
Adult Dose	Starting dose: 50 mg/d PO; increase gradually as tolerated, monitor blood levels; effective range approximately 2-3 mg/kg
Pediatric Dose	Administer as in adults
Contraindications	Documented hypersensitivity; low levels of serum thiopurine methyl transferase (TPMT)
Interactions	Toxicity increases with allopurinol; concurrent ACE inhibitors may induce severe leukopenia; may increase levels of MTX metabolites and decrease effects of anticoagulants, neuromuscular blockers, and cyclosporine
Pregnancy	D - Unsafe in pregnancy
Precautions	LFTs; reduce dose if platelet count <150 X 109/L or total neutrophil count <1 X 109/L; monitor blood parameters qwk initially, then each mo as stable dose achieved; total WBC count may be reduced to 4 X 109/L, and lymphocyte count may be reduced to about 7.5 X 109/L; some patients may have flu symptoms

FOLLOW-UP

Section 8 of 11  

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

Complications

• The main complications are related to involvement of organs other than the muscles, such as GI ulcerations, melena, hematemesis, or even infarctions affecting long stretches of the bowel, especially in dermatomyositis.
• A major problem with dermatomyositis can be the subcutaneous calcifications; when they protrude through the skin, they result in ulcerations, infections, and permanent disfiguring scars.
• In polymyositis, cardiac abnormalities and interstitial lung disease are common complications, especially in patients with anti–Jo-1 antibodies. Some studies have reported rates of these complications as high as 45%.

Prognosis

• The natural history of polymyositis and dermatomyositis is unknown because patients are now almost always treated with steroids.
• • Patients with interstitial lung disease may have a high mortality rate.
  • A number of patients still do not respond adequately to therapies and remain disabled.
  • Acute fulminating disease seems to be difficult to treat and resistant to therapies.
  • Patients in whom treatment is initiated soon after the onset of the symptoms have the best prognosis.
• When treatment is unsuccessful, the patient should be reevaluated and the muscle biopsy specimen reexamined.
• • A second biopsy may be considered to ensure that the diagnosis is correct.
  • The disorders most commonly mistaken for polymyositis are inclusion-body myositis and sporadic limb-girdle muscular dystrophy, which is suspected when the disease has a slow onset and progression and when the muscle-biopsy specimen does not show primary inflammatory features.

Patient Education

• The Myositis Association of America serves as a resource for patients and the medical community.
• Polymyositis/dermatomyositis at a glance
• • Polymyositis/dermatomyositis is a chronic inflammatory disease of muscle.
  • Muscle weakness is the most common symptom of polymyositis/dermatomyositis.
  • The cause of polymyositis/dermatomyositis is unknown.
  • Diagnosis of polymyositis/dermatomyositis involves physical examination of muscle strength, blood tests for muscle enzymes, electrical tests of muscle and nerves, and confirmation by muscle biopsy.
  • Treatment of polymyositis/dermatomyositis involves high doses of cortisone-related medications, immune suppression, and physical therapy.

MISCELLANEOUS

Section 9 of 11  

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

Medical/Legal Pitfalls

• The following may increase the medicolegal risk associated with the evaluation and management of this disorder:
• • Delay in diagnosis
  • Misdiagnosis
  • Failure to diagnose malignancy in dermatomyositis
  • Failure to inform patient about potential drug toxicity and medication adverse effects

Special Concerns

• Pregnancy
• • Polymyositis and dermatomyositis can occur in the last trimester of pregnancy or during puerperium; whether pregnancy is responsible for activating the disease is not known.
  • Pregnant women with dermatomyositis and polymyositis have been treated with steroids and have delivered healthy but small babies, though miscarriages and stillborn babies have also been reported.
• Overlap syndromes

MULTIMEDIA

Section 10 of 11  

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

Media file 1:  Hematoxylin and eosin paraffin section shows polymyositis. Longitudinal section shows a dense, chronic, endomysial inflammatory infiltrate. Image courtesy of Roberta J. Seidman, MD.
	View Full Size Image
Media type:  Photo

Media file 2:  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.
	View Full Size Image
Media type:  Photo

Media file 3:  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.
	View Full Size Image
Media type:  Photo

Media file 4:  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.
	View Full Size Image
Media type:  Photo

Media file 5:  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.
	View Full Size Image
Media type:  Photo

Media file 6:  Hematoxylin and eosin frozen section shows perifascicular atrophy in dermatomyositis. Fascicles in this sample show atrophy, predominantly at the periphery, along the connective-tissue border. Ischemia is considered to cause perifascicular atrophy. This finding is characteristic of dermatomyositis, mostly associated with the juvenile form but it is also observed in the adult form. Image courtesy of Roberta J. Seidman, MD.
	View Full Size Image
Media type:  Photo

Media file 7:  Immunofluorescence for membrane attack complex of complement (MAC) in dermatomyositis. Bright ring of yellow-green fluorescence at the center represents MAC in the wall of the microvessel. Finding was not present after treatment with steroids. Image courtesy of Roberta J. Seidman, MD.
	View Full Size Image
Media type:  Photo

REFERENCES

Section 11 of 11

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

• Banker BQ, Engel AG. The polymyositis and dermatomyositis syndrome. In: Myology. New York, NY:. McGraw-Hill;1986:1385-422.
• Bombardieri S, Hughes GR, Neri R, et al. Cyclophosphamide in severe polymyositis. Lancet. May 20 1989;1(8647):1138-9. [Medline].
• Cervera R, Ramirez G, Fernandez-Sola J, et al. Antibodies to endothelial cells in dermatomyositis: association with interstitial lung disease. BMJ. Apr 13 1991;302(6781):880-1. [Medline].
• Cherin P, Herson S, Wechsler B, et al. Efficacy of intravenous gammaglobulin therapy in chronic refractory polymyositis and dermatomyositis: an open study with 20 adult patients. Am J Med. Aug 1991;91(2):162-8. [Medline].
• Dalakas M. Treatment of polymyositis and dermatomyositis. Curr Opin Rheumatol. Dec 1989;1(4):443-9. [Medline].
• Dalakas MC, Rowland LP, DiMauro S. Inflammatory myopathies. In: Vinken PJ, Bruyn GW, Uchio E, eds. Handbook of Clinical Neurology. Vol 18. New York, NY:. Elsevier Science Inc;1992:369-90.
• Dalakas MC, Illa I, Dambrosia JM, et al. A controlled trial of high-dose intravenous immune globulin infusions as treatment for dermatomyositis. N Engl J Med. Dec 30 1993;329(27):1993-2000. [Medline].
• Emslie-Smith AM, Engel AG. Microvascular changes in early and advanced dermatomyositis: a quantitative study. Ann Neurol. Apr 1990;27(4):343-56. [Medline].
• Engel AG, Hohlfeld R, Banker BQ. The polymyositis and dermatomyositis syndrome. In: Myology. New York, NY:. McGraw-Hill;1994:1335-83.
• Grau JM, Herrero C, Casademont J, et al. Cyclosporine A as first choice therapy for dermatomyositis. J Rheumatol. Feb 1994;21(2):381-2. [Medline].
• Illa I, Dinsmore S, Dalakas MC. Immune-mediated mechanisms and immune activation of fibroblasts in the pathogenesis of eosinophilia-myalgia syndrome induced by L-tryptophan. Hum Pathol. Jul 1993;24(7):702-9. [Medline].
• Koski CL, Patterson JV. Intravenous immunoglobulin use for neurologic diseases. J Infus Nurs. May-Jun 2006;29(3 Suppl):S21-8.
• Lang BA, Laxer RM, Murphy G, et al. Treatment of dermatomyositis with intravenous gammaglobulin. Am J Med. Aug 1991;91(2):169-72. [Medline].
• Marinelli WA, Leatherman JW. Neuromuscular disorders in the intensive care unit. Crit Care Clin. Oct 2002;18(4):915-29, x. [Medline].
• Miller FW, Leitman SF, Cronin ME, et al. Controlled trial of plasma exchange and leukapheresis in polymyositis and dermatomyositis. N Engl J Med. May 21 1992;326(21):1380-4. [Medline].
• Otero C, Dalakas MC. Onset of polymyositis (PM) and dermatomyositis (DM) during pregnancy: report of 4 cases. Ann Neurol. 1992;32:282.
• Pellissier JF, Civatte M, Fernandez C, et al. [Dermatomyositis and polymyositis]. Rev Neurol (Paris). Oct 2002;158(10 Pt 1):934-47. [Medline].
• Rowland LP. Polymyositis, inclusion body myositis, and related myopathies. In: Merritt's Neurology. 10th ed. Philadelphia, Pa:. Lippincott Williams & Wilkins;2000:765-9.
• Stein DP, Dalakas MC. Intercellular adhesion molecule-1 expression is up regulated in patients with dermatomyositis (DM) [abstract]. Ann Neurol. 1993;34:268.
• Targoff IN. Immune mechanisms in myositis. Curr Opin Rheumatol. Dec 1990;2(6):882-8. [Medline].
• Targoff IN, Reichlin M. Measurement of antibody to Jo-1 by ELISA and comparison to enzyme inhibitoryactivity. J Immunol. May 1 1987;138(9):2874-82. [Medline].
• Whitaker JN, Engel WK. Vascular deposits of immunoglobulin and complement in idiopathic inflammatory myopathy. N Engl J Med. Feb 17 1972;286(7):333-8. [Medline].

Article Last Updated: Nov 14, 2006