INTRODUCTION — Dermatomyositis (DM) and polymyositis (PM) are immune-mediated myopathies, characterized by the shared features of proximal skeletal muscle weakness and evidence of muscle inflammation [1-4]. DM, unlike PM, is associated with a variety of characteristic skin manifestations. A form of DM termed clinically amyopathic DM (CADM; historically termed "dermatomyositis sine myositis") is a condition in which patients have characteristic skin findings of DM without clinically significant muscle disease. (See "Cutaneous dermatomyositis in adults: Overview and initial management".)
The three other major immune-mediated myopathies are antisynthetase syndrome, immune-mediated necrotizing myopathy (IMNM), and inclusion body myositis (IBM). IMNM shares clinical findings and some serologic markers with DM and PM, while both IMNM and IBM have histopathologic findings on muscle biopsy that distinguish them from DM and PM. (See "Clinical manifestations and diagnosis of immune-mediated necrotizing myopathy" and "Clinical manifestations and diagnosis of inclusion body myositis".)
The clinical manifestations of DM and PM in adults will be reviewed here. Separate topic reviews related to DM, PM, and other inflammatory myopathies in adults include the following:
Related disorders that occur in children (known as juvenile DM and PM) are discussed separately:
EPIDEMIOLOGY — Dermatomyositis (DM) and polymyositis (PM) are relatively uncommon disorders.
Dermatomyositis — In a population-based study of the residents of Olmsted County in Minnesota that included patients diagnosed with DM from 1995 to 2019, the annual incidence of all subtypes of DM was 1.1 per 100,000 person-years, and prevalence was 13 per 100,000. The estimated annual incidence for the clinically amyopathic subtype of DM (CADM) was 0.5 per 100,000 person-years .
The risk of DM increases with each decade of life. Among patients in this study who were at least 80 years old, the incidence of DM was 3.2 per 100,000 person-years.
The incidence of DM was also higher in females compared with males (20 versus 3.7 per 100,000 person-years).
Polymyositis — The annual incidence of PM has been reported to be 0.41 to 0.75 per 100,000 persons [6,7]. Precise measurement of rates of PM is difficult due to the limitations of diagnostic criteria used in epidemiologic studies. A female-to-male predominance in PM has also been reported . PM affects mostly adults and is rare in the pediatric population .
There is growing understanding that the term PM is falling out of favor given the increased understanding that many cases that would previously be classified as PM are now better classified as the antisynthetase syndrome (without a characteristic rash), overlap myositis (with another connective tissue disease), or immune-mediated necrotizing myopathy (IMNM). While it is now understood that muscle biopsy features are distinct in IMNM, previous studies often labeled these cases as PM, assuming the primary inflammation had been missed on the muscle biopsy sampling.
Muscle biopsies are not required for a diagnosis of "probable PM" for those cases diagnosed by outdated Bohan and Peter criteria. However, a muscle biopsy should be performed on all cases of "possible PM" to ensure the patient does not have some other form of inflammatory myositis (eg, inclusion body myositis [IBM], IMNM) or other myopathy (eg, dystrophy, metabolic, congenital).
Clinical features — The cardinal manifestation of dermatomyositis (DM) and polymyositis (PM) is skeletal muscle weakness, specifically symmetric proximal muscle weakness [10,11]. All DM and PM patients exhibit this cardinal feature other than a subset referred to as clinically amyopathic DM (CADM), in which characteristic cutaneous manifestations are present in the absence of clinically evident muscle weakness. (See "Cutaneous dermatomyositis in adults: Overview and initial management", section on 'Overview of clinical features'.)
DM patients also exhibit a variety of characteristic skin manifestations and are at increased risk for an underlying malignancy. Interstitial lung disease (ILD), constitutional signs and symptoms, dysphagia, and inflammatory arthritis may also be present in variable frequency in different serologic subsets defined by myositis-specific autoantibodies. These clinical features are described in further detail below.
Muscle weakness — Muscle weakness is the most common feature of DM and PM; over 90 percent of patients with PM present with muscle weakness . However, in DM, cutaneous manifestations often precede or accompany weakness, which is found at presentation in only 50 to 60 percent of patients [10,11]. Myalgias and muscle tenderness occur in 25 to 50 percent of cases. Patients may notice joint pain and swelling, and they occasionally mistakenly ascribe weakness to the joint involvement. Pain is mild to moderate, if present, and stiffness is not a prominent complaint.
●Distribution – The distribution of weakness is characteristically symmetric and proximal in both PM and DM. Affected muscles typically include the deltoids, hip flexors, abductors, and extensors. Weakness of the neck flexors with relative sparing of the neck extensors is also common.
Distal muscle weakness, if present, tends to be milder than proximal muscle weakness and usually does not cause significant functional impairment. Rarely, patients present with focal myositis that usually but not always progresses to the typical generalized form over time . Muscle atrophy is generally not seen in early cases, even in patients with marked weakness, but it may occur in severe, longstanding disease.
●Course – Patients usually report a history of the insidious or subacute development of the muscle weakness, with gradual worsening over a period of several weeks to months before medical attention is sought. However, an acute onset of weakness is occasionally reported. Patients may describe increasing difficulty climbing stairs, getting up from a chair, carrying groceries, lifting a gallon of milk, or picking up their children due to the proximal muscle involvement.
Skin findings in dermatomyositis — Several distinct cutaneous findings occur in DM [13,14]. Cutaneous manifestations may be prominent in some patients, but can be quite subtle in others. Patients frequently present with some of these features, but not all.
Characteristic findings — Gottron papules and the heliotrope eruption are pathognomonic features of DM. Gottron sign, photodistributed erythema, poikiloderma, nailfold changes, scalp involvement, and calcinosis cutis are also characteristic and useful in distinguishing DM from PM.
●Gottron papules – Gottron papules are erythematous to violaceous papules that occur symmetrically over bony prominences, particularly the extensor (dorsal) aspects of the metacarpophalangeal (MCP) and interphalangeal (IP) joints (picture 1A-C). In addition, these lesions may involve the skin between the MCP and IP joints, so-called linear extension, particularly when the eruption is prominent. Sites such as the elbows and knees may also be affected.
Gottron papules often have associated scale and may ulcerate. When scaling is present, the lesions may mimic psoriasis or lichen planus.
●Gottron sign – Definitions used for Gottron sign have varied in the literature . We define Gottron sign as the presence of erythematous to violaceous macules, patches, or papules on the extensor surfaces of joints of the elbows, knees, or ankles (picture 2).
●Heliotrope eruption – The heliotrope eruption is an erythematous to violaceous eruption on the periorbital skin. Although it is most common on the upper eyelid, it can also involve the lower eyelid as well, sometimes accompanied by edema, which, at times, may be quite marked (picture 3A-D).
●Facial erythema – Patients may have midfacial erythema that can mimic the malar erythema seen in systemic lupus erythematosus (SLE) (picture 3A, 3E). In contrast to those with SLE, however, patients with DM will have midfacial erythema that involves the nasolabial folds (rather than the classic nasolabial sparing seen in the malar rash of SLE), which can be helpful in distinguishing these two photosensitive midfacial eruptions.
●Photodistributed poikiloderma (including the shawl and V-signs) – Poikiloderma refers to skin that demonstrates both hyperpigmentation and hypopigmentation, as well as telangiectasias and epidermal atrophy. In DM, patients may demonstrate poikiloderma in any photo-exposed site; however, classic areas of involvement are the upper back (shawl sign) (picture 4A-B) and the V of the neck and upper chest (V-sign). The poikiloderma in DM often presents with a violaceous hue but may be more erythematous in patients with lighter skin. In patients with darker skin types, the most noticeable component of the eruption may be hyperpigmentation, including on presentation.
Early in the course of cutaneous disease, these areas may demonstrate only erythema rather than well-developed poikiloderma (picture 4C). The erythema may be macular (nonpalpable) or papular. The cutaneous eruption of DM is often associated with significant pruritus, which may assist in distinguishing its photo-exacerbated eruption from that of SLE, which is typically nonpruritic.
●Holster sign – Patients with DM may also have poikiloderma on the lateral aspects of the thighs, referred to as the "Holster sign" (picture 5A-B). It is unclear why this cutaneous manifestation occurs on this classically photo-protected site.
●Nailfold abnormalities – Multiple nailfold capillary changes are often seen in DM. Abnormal capillary nailbed loops with alternating areas of dilatation and dropout, as well as periungual erythema, are common (picture 6A-B). In addition, cuticular hypertrophy, sometimes termed "ragged cuticles," is also characteristic and may be associated with hemorrhagic infarcts within the hypertrophic area (picture 6A). The degree of cuticular involvement is thought to reflect ongoing cutaneous disease activity, representing active vasculopathy .
●Psoriasiform changes in scalp – The scalp involvement in DM typically includes poikilodermatous changes and prominent scaling (picture 7). These changes often mimic seborrheic dermatitis or psoriasis. Scalp involvement may result in severe burning, pruritus, and/or sleep disturbance. In addition, severe scalp pruritus may occur in patients without clinically evident psoriasiform changes.
●Mechanic's hands – Hyperkeratosis and fissuring of the palms and lateral fingers.
●Calcinosis cutis – The deposition of calcium within the skin occurs more commonly in juvenile DM than in adult DM. Calcinosis cutis, which is very challenging to treat, may be seen in a variety of conditions, including systemic sclerosis (SSc, scleroderma), particularly the limited form of cutaneous SSc; SLE (rarely); and overlap connective tissue disorders. It is more common in patients with DM with the anti-MJ/anti-NXP-2 myositis-specific autoantibodies [17,18]. Patients with anti-PM-Scl antibodies may present with a characteristic DM eruption and calcinosis. (See "Calcinosis cutis: Etiology and patient evaluation".)
●Generalized erythroderma – Rarely, erythroderma may occur, which involves extensive cutaneous surface area, including areas that are less exposed to ultraviolet light. (See "Erythroderma in adults".)
MDA5-associated dermatomyositis — Patients with MDA5 antibodies are known to have a characteristic phenotype with findings that include :
●Cutaneous ulceration overlying Gottron papules, Gottron sign, lateral nailfolds, and digital pulp (including digital necrosis)
●Erythematous, painful palmar macules and papules, predominantly over the finger creases and palms; livedoid eruption on the palms and occasionally feet
●Prominent nonscarring alopecia
●Lower incidence of myositis
●Higher risk for ILD, including a rapidly progressive presentation with high mortality
Recognition of the cutaneous features of MDA5-associated DM is critical for identifying patients who may benefit from close monitoring of pulmonary status, particularly in the absence of widely available autoantibody testing . (See "Interstitial lung disease in dermatomyositis and polymyositis: Clinical manifestations and diagnosis".)
Rare findings — Rarely reported cutaneous findings in patients with DM have included panniculitis, cutaneous vasculitis, porcelain white atrophic scars (ie, Degos disease-like lesions), vesicle and bullae formation, ichthyosis, follicular hyperkeratosis, malakoplakia, papular mucinosis, and flagellate erythema [13,14,21-23]. Diffuse nonpitting edema is another rare manifestation of DM and may be a marker of more aggressive disease .
Interstitial lung disease — ILD occurs in at least 30 to 40 percent of cases of DM and PM, most often in association with anti-Jo-1 or another antisynthetase antibody (eg, anti-PL-7 or anti-PL-12). In DM, it can be observed in patients with either classic or amyopathic disease. A rapidly progressive ILD associated with pulmonary failure and death is most commonly a feature of anti-MDA5 DM. (See "Overview of and approach to the idiopathic inflammatory myopathies", section on 'Myositis-specific autoantibodies'.)
In addition to ILD, respiratory insufficiency in the immune-mediated myopathies may result from diaphragmatic and chest wall muscle weakness. These issues are discussed in detail separately. (See "Interstitial lung disease in dermatomyositis and polymyositis: Clinical manifestations and diagnosis".)
Esophageal involvement — Dysphagia is the most commonly reported gastrointestinal symptom, with studies reporting a wide range in prevalence . Weakness of the striated muscle of the upper one-third of the esophagus and/or the oropharyngeal muscles contribute to dysphagia, nasal regurgitation, and/or aspiration . Esophageal involvement is more common in older patients and may underlie the increased incidence of bacterial pneumonia .
Cardiac involvement — Cardiac involvement with histologic evidence of myocarditis is well described in DM and PM, and subclinical manifestations are frequent, including conduction abnormalities and arrhythmia detected by electrocardiographic studies [28,29]. Symptomatic cardiac disease, such as congestive heart failure, is less common . However, patients with DM and PM are also at increased risk for myocardial infarction (MI) [31,32]. A large, retrospective, population-based study found a nearly three- and fourfold increased risk of MI among 350 and 424 patients with incident DM and PM, respectively, as compared with those without an inflammatory myopathy, after controlling for relevant risk factors such as age, sex, glucocorticoids, and nonsteroidal antiinflammatory drugs (NSAIDs) .
Association with malignancy — An increased rate of malignancy has been described, with a greater risk in patients with DM, especially those with the TIF1 gamma autoantibody. The spectrum of malignancies generally parallels the distribution in the general population with a few possible exceptions. This issue is discussed in detail separately. (See "Malignancy in dermatomyositis and polymyositis".)
Laboratory findings — Several laboratory findings are characteristic of DM and PM, including:
●Elevated levels of muscle enzymes. (See 'Muscle enzymes' below.)
●Autoantibodies, including antinuclear antibodies, in up to 80 percent of patients with DM and PM [10,11,33,34]; myositis-specific autoantibodies in at least 45 to 85 percent of patients ; and myositis-associated autoantibodies, especially in patients with overlap syndromes. While most myositis-specific autoantibodies associated with DM are nuclear in origin, anti-MDA5 is cytoplasmic. Similarly, the antisynthetase autoantibodies such as anti-Jo-1 are also located in the cytoplasm. (See 'Myositis-specific autoantibodies' below and 'Myositis-associated autoantibodies' below.)
●The erythrocyte sedimentation rate (ESR) is often normal or is only mildly elevated, even in patients with active muscle disease . An elevated ESR may be seen in concomitant inflammatory arthritis or with myositis-associated ILD .
Muscle enzymes — Creatine kinase (CK), lactate dehydrogenase (LDH), aldolase, aspartate aminotransferase (AST), and alanine aminotransferase (ALT) are all muscle enzymes that may be elevated in patients with inflammatory myopathy and other muscle disorders. (See "Muscle enzymes in the evaluation of neuromuscular diseases".)
At some point in the course of the disease, almost all patients with DM and PM, except those with CADM, have an elevation in at least one muscle enzyme; most have elevations in all enzymes. In a review of 153 patients with DM or PM, normal results were found for CK in 5 percent, for aldolase in 4 percent, for LDH in 9 percent, and for the aminotransferases in 15 to 17 percent . However, these data may underestimate the frequency of normal CK concentrations because the Bohan and Peter criteria employed in that study included muscle enzyme elevation as a disease criterion. Additionally, the study was performed before many autoantibody tests and magnetic resonance imaging (MRI) studies were available to facilitate the diagnosis. (See "Overview of and approach to the idiopathic inflammatory myopathies", section on 'Classification criteria'.)
●Creatine kinase – The level of serum CK can vary widely. In untreated patients with active muscle disease, it can be more than 10-fold the upper limit of normal (ie, at least 2000 to 3000 international units/L), although some patients, particularly those with DM, may present with normal muscle enzymes despite significant muscle involvement. In severe cases, the serum CK concentration may be elevated more than 50-fold or even 100-fold (ie, up to 10,000 to 20,000 international units/L), and higher levels are sometimes seen. This is most often the case when there is a prominent degree of muscle necrosis present.
There is no clear correlation with CK and severity of weakness, though the level is useful to follow during treatment. In some cases, there may be elevations in serum muscle enzymes without discernible muscle weakness. This is particularly observed in patients with early disease.
The occurrence of muscle weakness with relatively normal enzyme levels is much more likely to occur in DM than PM. Persistently low serum muscle enzyme levels in the setting of obvious muscle weakness may also occur in patients with advanced disease and significant loss of muscle mass. In these groups of patients, assessments other than enzyme levels can be beneficial, including a non-contrast muscle MRI with T1 and short tau inversion recovery (STIR) sequences, typically performed on the bilateral thighs. Other patients with no clinical muscle involvement, as in CADM, will also have normal or near-normal muscle enzyme levels.
●Aldolase – Aldolase is another glycolytic pathway enzyme that is found in all tissues but predominantly in skeletal muscle, liver, and brain. While increased aldolase levels are not as specific or sensitive for muscle disease as CK levels, aldolase concentrations are occasionally elevated in patients with myositis, particularly with prominent perimysial pathology, who have normal CK levels . Aldolase levels are often also elevated when there is significant fasciitis present, which can be observed in DM.
●CK-MB – Patients with myositis may also have an elevated serum creatine kinase-myocardial band (CK-MB) fraction. This may occur in the absence of myocarditis, which is usually attributed to increased expression in regenerating skeletal muscle affected by the inflammatory disease or, less often, to involvement of the myocardium by the myositis. MI may be suspected in these patients, who may require additional testing. Measurement of cardiac troponin I may be helpful in patients in whom it may be difficult clinically to determine whether elevations in CK or other muscle enzymes are due to cardiac rather than skeletal muscle disease. Increased levels of cardiac troponin I appear relatively specific for myocardial injury, unlike elevations of total CK, CK-MB, and other muscle enzymes or of cardiac troponin T, all of which may be seen both in skeletal muscle inflammatory myopathy and in cardiac disease [34,36,39-41]. (See 'Cardiac involvement' above and "Troponin testing: Clinical use".)
●Aminotransferases – Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) may be elevated in patients with myositis, and can sometimes result in an unnecessary workup for liver dysfunction. Gamma-glutamyl transpeptidase (GGT) is a transaminase that is not present in skeletal muscle, and when also elevated, and can sometimes be used to help clarify whether elevations in AST and ALT are related to underlying liver dysfunction rather than skeletal muscle involvement. (See "Overview of and approach to the idiopathic inflammatory myopathies", section on 'Muscle enzymes'.)
Myositis-specific autoantibodies — Myositis-specific autoantibodies are detected primarily in patients with immune-mediated myopathy and are associated with unique clinical phenotypes within the myositis spectrum, and may be associated with certain histopathologic findings . It is not known whether such autoantibodies have a direct role in disease pathogenesis. Myositis-specific autoantibodies may be present in 45 to 85 percent of patients . Many experts use a myositis autoantibody panel to determine what particular myositis phenotype may best fit the patient rather than to make a diagnosis of myositis. There is no standardization among many available autoantibody platforms, which may lead to false positives or false negatives; it is imperative that the clinician remain aware of this limitation, particularly when the clinical phenotype is inconsistent with the autoantibody test result. A more detailed discussion of the myositis-associated autoantibodies and the disease associations can be found separately. (See "Overview of and approach to the idiopathic inflammatory myopathies", section on 'Myositis-specific autoantibodies'.)
Myositis-associated autoantibodies — Myositis-associated autoantibodies are those found in patients with other systemic rheumatic diseases that can be associated with myositis. A more detailed discussion of myositis-associated autoantibodies is presented separately. (See "Overview of and approach to the idiopathic inflammatory myopathies", section on 'Myositis-associated autoantibodies'.)
The detection of anti-Ro, anti-La, or anti-ribonucleoprotein (RNP) autoantibodies in a patient with myositis suggests a diagnosis of myositis associated or overlapping with another systemic rheumatic disease . Anti-Ro52 autoantibodies are more common in patients with antisynthetase antibodies, whereas anti-Ro60 and anti-La may be seen in a smaller number of such patients and in those with other myositis-specific autoantibodies. The presence of anti-Ro52 autoantibodies in patients with DM appears to be a risk factor for ILD [43,44]. (See "The anti-Ro/SSA and anti-La/SSB antigen-antibody systems" and "Antibodies to double-stranded (ds)DNA, Sm, and U1 RNP".)
In general, anti-Ro, anti-La, and anti-U1 RNP can be seen in some patients who also have myositis-specific autoantibodies, but myositis-specific autoantibodies tend to be mutually exclusive with each other. High titers of anti-RNP antibodies are associated with mixed connective tissue disease, an overlap syndrome of myositis with features of SSc and SLE . (See "The anti-Ro/SSA and anti-La/SSB antigen-antibody systems", section on 'Anti-Ro60 versus anti-Ro52 antibodies' and "Mixed connective tissue disease".)
Anti-PM-Scl and anti-Ku autoantibodies have been identified in patients with overlapping features of myositis and SSc . Many patients with these antibodies, however, do not have myositis . (See "Measurement and clinical significance of antinuclear antibodies", section on 'Nuclear speckled' and "Neuromuscular manifestations of systemic sclerosis (scleroderma)", section on 'Laboratory testing'.)
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Dermatomyositis and polymyositis".)
INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)
●Beyond the Basics topics (see "Patient education: Polymyositis, dermatomyositis, and other forms of idiopathic inflammatory myopathy (Beyond the Basics)")
●Definitions – Dermatomyositis (DM) and polymyositis (PM) are both multisystem disorders with a wide variety of clinical manifestations. The term PM is now understood to encompass a much smaller subset of inflammatory myopathies as more specific phenotyping has evolved. Most patients exhibit proximal skeletal muscle weakness and evidence of muscle inflammation, but the immune mechanisms and the anatomic focus of injury within the muscle tissue in DM and PM appear distinct. (See 'Introduction' above.)
•Muscle weakness – The muscle weakness usually develops in an insidious or subacute fashion, with gradual worsening over a period of several months. Oropharyngeal and upper esophageal muscle involvement may lead to dysphagia, nasal regurgitation, or aspiration. Respiratory failure may result from weakness of the diaphragm and chest wall muscles. (See 'Clinical features' above and 'Muscle weakness' above.)
•Skin findings in DM – Several characteristic skin eruptions are typical of DM, including Gottron papules and the heliotrope eruption (picture 1A, 3A); these changes are considered pathognomonic for DM. Photodistributed erythema and poikiloderma, as well as nailfold changes, are also characteristic and useful in distinguishing DM from PM (picture 4A-C, 6A-B). A form of DM, termed clinically amyopathic DM (CADM; historically known as "dermatomyositis sine myositis"), is a condition in which patients have characteristic skin findings of DM without weakness, abnormal muscle enzymes, or other abnormal muscle studies. (See 'Skin findings in dermatomyositis' above and "Cutaneous dermatomyositis in adults: Overview and initial management".)
•Interstitial lung disease – Interstitial lung disease (ILD) occurs in 30 to 40 percent of cases of DM and PM. In DM, it can be observed in patients with either classic or amyopathic disease. The occurrence of ILD may be associated with rapidly progressive pulmonary failure and death. (See 'Interstitial lung disease' above.)
●Association with malignancy – The risk of malignancy may be increased, particularly in patients with DM. (See 'Association with malignancy' above.)
•Muscle enzymes – Elevations in serum creatine kinase (CK), lactate dehydrogenase (LDH), aldolase, and aminotransferases occur in most patients with DM and PM. (See 'Muscle enzymes' above.)
•Autoantibodies – Autoantibodies are found in a majority of patients. Myositis-specific autoantibodies may be present in at least 20 to 40 percent of patients. Myositis-associated autoantibodies are those found in patients with other systemic rheumatic diseases that can be associated with myositis. (See 'Myositis-specific autoantibodies' above and 'Myositis-associated autoantibodies' above.)
ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Marc L Miller, MD, who contributed to an earlier version of this topic review.
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