Pathogenesis And Clinical Manifestations Of Juvenile Dermatomyositis And Polymyositis
Pathogenesis and clinical manifestations of juvenile dermatomyositis and
Clare Hutchinson, MDCM, FRCPC
Brian Feldman, MD Section Editors
Thomas JA Lehman, MD
Jeremy M Shefner, MD, PhD Deputy Editor
Melanie S Kim, MD
Last literature review version 17.1: January 2009 | This topic last updated: February 9,
INTRODUCTION — Juvenile dermatomyositis (JDM) and juvenile polymyositis (JPM) are rare
autoimmune myopathies in childhood. JDM is primarily a capillary vasculopathy, whereas JPM
involves direct T-cell invasion of muscle fibers similar to that seen in adult polymyositis [1,2] . (See
"Clinical manifestations and diagnosis of adult dermatomyositis and polymyositis").
The epidemiology, pathogenesis, and clinical manifestations of JDM and JPM will be reviewed
here. Diagnosis and treatment of these disorders are discussed elsewhere. (See "Diagnosis of
juvenile dermatomyositis and polymyositis" and see "Treatment of juvenile dermatomyositis and
EPIDEMIOLOGY — JDM is the most common idiopathic inflammatory myopathy of childhood
accounting for approximately 80 percent of cases [3,4] . In population-based studies, JDM has a
reported annual incidence that ranges from two to four cases per one million children [5-9] . The
peak incidence is from 5 to 10 years of age [8, 9]. Girls are affected more often than boys with a
two- to five-fold greater rate [7,8,10] .
JPM occurs less frequently and accounts for only 3 to 6 percent of childhood idiopathic
inflammatory myopathies [3,7] .
PATHOGENESIS — Although the etiology remains unclear, it has been proposed that JDM and JPM
are caused by an autoimmune reaction within the muscle tissue of genetically susceptible
individuals, possibly in response to environmental triggers.
Genetic susceptibility — The occurrence of JPM and JDM in monozygotic twins and first-degree
relatives suggests a genetic predisposition to these disorders in some families [11,12] . Certain HLA
alleles also have been reported to be more common in patients with JDM; these include HLA-B8,
HLA-DQA1*0501 and HLA-DQA1*0301 [13-15] . However, investigation of HLA class II alleles in
patients with JDM has not identified any disease-associated allele  .
Non-HLA associated genes, including genetic polymorphisms in tumor necrosis factor-alpha and
interleukin-1 receptor antagonist, are known risk factors for the development of JDM or for the
severity of its presentation [17-19] .
Immunologic mechanisms — The following findings support the role of the immune system in the
pathogenesis of JDM and JPM: T cell invasion of muscle fibers in patients with JPM  .
Antinuclear antibodies are present in about 70 percent of patients with JDM and JPM. The specific
antigen(s) for these antibodies have not yet been identified  .
Myositis-specific autoantibodies (MSAs) are found in a minority of adults with DM and PM and are
associated with specific clinical subgroups. However, MSAs have been identified in only a small
number of children with inflammatory myopathy [21,22] . In one study of 38 children with JDM
and other connective tissue diseases, MSAs were identified in 12 of 77 serum samples  . In a
second study, MSAs (specifically anti Mi-2 autoantibodies) were found in only 2 of 42 patients with
JDM. (See "Clinical manifestations and diagnosis of adult dermatomyositis and polymyositis",
section on Myositis-specific autoantibodies). Similarity of observed histologic changes between
JDM and chronic graft-versus-host disease. The presence of persistent maternal cells (maternal
microchimerism), which triggers an immunologic response, has been proposed as a common
pathogenetic pathway for the two disorders. Two studies have reported evidence of maternal
microchimerism in the peripheral blood and muscle biopsies of boys with juvenile inflammatory
myopathy [23,24] . Experimental data demonstrating increased T cell reactivity of in vitro
peripheral blood mononuclear cells to heat shock protein (HSP) 60 in patients compared to normal
controls  . HSPs have been proposed to have a regulatory role in chronic inflammatory
diseases and may be an autoantigen for these disorders. (See "Immunopathogenesis of juvenile
rheumatoid arthritis", section on Gamma-delta-T-Cell).
Infection — Several observations have suggested that JDM may develop as an unusual response to
infection in a genetically susceptible host: There is an increased prevalence of Coxsackie B
antibodies in children with JDM compared to matched controls  . Case reports of viral isolation
from muscle specimens in adult myositis have been described  . There is an association
between echovirus infection and chronic polymyositis in children with agammaglobulinemia  .
A seasonal variation of onset in JDM exists, with clustering of cases in the spring and summer  .
Epitopes that are common both to human skeletal muscle and the bacteria Streptococcus
pyogenes have been shown to be targets for cytotoxic T cell responses in patients with early,
active JDM, indicating a possible link between an immune response to bacteria and the
development of myositis  . Respiratory and gastrointestinal complaints and/or antibiotic use
are common in the three months before diagnosis of JDM [31,32] .
However, attempts at demonstrating a viral etiology of JDM have failed. As an example, a recent
study of 79 patients with new onset JDM found normal antibody titers to Herpes simplex virus,
Coxsackievirus B 1 through 6, and Toxoplasma gondii  . Another report using the polymerase
chain reaction was unable to demonstrate evidence of viral genetic material in the muscle of 20
individuals with active, untreated recent onset JDM  .
Malignancy — Unlike adults, children with JDM or JPM do not have an increased risk of
malignancy. In one Scottish population-based study, for example, cancer was not observed among
35 and 9 children with JDM or JPM, respectively  . There are rare case reports of solid tumors
or hematologic malignancies in children with JDM; however, nothing suggests that the incidence
of these disorders is greater than in the general population. (See "Malignancy in dermatomyositis
Based upon these data, unless the presenting features are quite unusual, a search for malignancy
does not need to be made when children present with idiopathic inflammatory myopathy.
CLINICAL MANIFESTATIONS — Muscle weakness is the hallmark of JDM and JPM. In addition,
patients with JDM present with characteristic rashes (show picture 1). Children with JDM and JPM
also may have constitutional symptoms (fever, weight loss, fatigue, and headache), which may be
the initial finding prior to the onset of muscle weakness, and in patients with JDM, rash.
Because JPM is a rare entity, there is little descriptive clinical information about this disorder. This
discussion will mainly focus on the clinical manifestations of JDM.
The clinical presentation of JDM is exemplified by the two following case series. In the first review
from a single tertiary Canadian center of 105 patients with JDM (mean age at diagnosis 7.6 years),
the most common symptoms/findings and their frequency were noted at disease onset  .
Gottron's rash: 91 percent Heliotrope rash: 83 percent Malar/facial rash: 42 percent Nailfold
capillary change: 80 percent Myalgia/arthralgia: 25 percent Dysphonia or dysphagia: 24 percent
Anorexia: 18 percent Fever: 16 percent
The second case series is from the JDM Research Registry and included 166 newly diagnosed
children living in the continental United States from 1994 to 1999  . The mean age of diagnosis
was 7.5 ± 3.8 years, and the median duration of symptoms prior to diagnosis was four months.
There was no difference in the age of diagnosis or duration of untreated disease based upon
gender or ethnicity. The initial symptoms were rash in 65 percent, weakness alone in 29 percent,
or both rash and weakness in 6 percent of patients. The severity of the weakness increased with
the duration of symptoms prior to diagnosis. Both the height and weight were lower compared to
normative data from the National Health and Nutrition Examination Study (NHANES) III survey.
Other findings included capillary dilation, arthritis, difficulty swallowing, abdominal pain, and
Cutaneous manifestations — Cutaneous manifestations are common in children with JDM and
include a characteristic heliotropic rash, gottron's papules, nailfold capillary changes, calcinosis,
and skin ulcerations (show picture 2).
Rash — Several distinct rashes (ie, heliotrope rash and Gottron's papules) may occur
simultaneously with muscle involvement but can also be prominent prior to obvious muscular
weakness. Rash is an important distinguishing feature between JDM and JPM, as it is not present
in the latter condition. Skin disease may be exacerbated by exposure to sunlight and, as such, sun
protection should be part of routine care in JDM. Heliotrope dermatitis is a reddish-purple rash on
the upper eyelids, often accompanied by swelling of the eyelid (show picture 1). Malar and facial
erythema may also be present. Heliotrope rash is one of the most common finding in patients with
JDM, with a reported rate of 83 percent in the previously mentioned Canadian study, and a 94
percent rate in 44 patients from Hungary [4,36] . Periorbital edema, upper lid edema, or
telangiectasia of the eyelid capillaries can be seen in 50 to 90 percent of children [37,38] .
Gottron's papules are an erythematous, papulosquamous eruption over the dorsal surfaces of the
knuckles (show picture 1). The term "Gottron's sign" is often used if the lesions are not papular.
Similar lesions can occur over the extensor aspects of the elbows, knees, and medial malleoli, at
times mimicking psoriasis. Gottron's papules are a common feature in patients with JDM, with a
reported rate of 91 percent of Canadian and 77 percent of Hungarian patients from the previously
mentioned studies [4,36] .
Nailfold capillary changes — Nailfold capillary changes may be observed at the bedside or in clinic.
These include capillary dilatation, tortuosity and dropout. The measured density of capillaries/mm
may be a useful tool for monitoring clinical activity in JDM  (show picture 2, panel C).
Skin ulcerations — Ulcerative skin disease is a serious and potentially life-threatening
manifestation of JDM (show picture 2, panel E). Ulcers presumably reflect significant vasculopathy
in the skin (with tissue hypoxia and necrosis), and may signal vasculopathy in other organs
(especially the lungs and gut). Patients with ulcerative lesions have more severe disease and a
This was illustrated by a retrospective case series that included 6 of 47 children with JDM with
extensive ulcerative skin vasculitis present at diagnosis  . These six patients continued to have
persistent muscle weakness, elevations of muscle enzyme activity, and severe generalized
cutaneous vasculitis despite receiving corticosteroid therapy. In another study, 10 of 29 patients
had a chronic disease course characterized by ulcerative cutaneous and gastrointestinal lesions
 . Two of the 10 died due to complications including gastrointestinal perforation, five had
severe musculoskeletal and cutaneous damage, and three had no residual disease  .
Calcinosis — Dystrophic calcification or calcinosis (soft tissue calcification) generally develops
within a few years of diagnosis (show picture 2, panel D) [3,42] . Reports of its prevalence vary
from 30 to 50 percent [40,43] . In contrast, one study of 144 patients from the United Kingdom
reported a much lower calcinosis rate of 6 percent  .
Five distinct patterns of calcinosis have been described [40,44] : Small, scattered, superficial
plaques or nodules, usually on the extremities. These lesions often do not interfere with function,
but may be painful and may develop spontaneous cellulitis-like inflammation (sometimes with
drainage of toothpaste-like calcium soap). Inflamed superficial calcinosis must be differentiated
from superinfected lesions. Superficial calcinosis often regresses spontaneously over a period of
years. Deep tumoral muscle calcification often found in the proximal muscle groups that may
interfere with joint motion. These deposits may ulcerate or extrude calcific material through the
skin. These may require surgical debridement in order to maximize joint function. Diffuse deposits
along myofascial planes that may limit joint motion and may be painful. Mixed forms of the above
three types may be seen. Extensive exoskeleton-like calcium deposits that result in serious
limitations in function. Patients with this form of calcinosis often have a history of severe,
unremitting disease course associated with ulcerative cutaneous disease.
Calcinosis has been associated with the following risk factors: Delay in diagnosis or treatment, or
inadequate treatment [40,45] . Tissue necrosis factor (TNF) alpha-308A genotype (this allele is
associated with increased levels of TNF alpha)  . Patients below five years of age have been
reported to be more likely to develop calcinosis  . However, another study found no
association between age of onset of JDM and calcinosis.
Amyopathic dermatomyositis — The cutaneous manifestations of JDM may appear in the absence
of clinically apparent muscle disease in a small number of children. Children with this
presentation, termed amyopathic JDM, may never develop muscle weakness, but amyopathic JDM
may reflect an early phase in the disease course before muscle weakness has yet developed. The
skin findings may require therapy but may remit in some without systemic therapy [47-49] .
However, all such children require evaluation by an experienced pediatric rheumatologist or
neurologist to assure that they are not, in fact, weak.
Muscle weakness — The inflammatory myopathies are characterized by symmetric, proximal
muscle weakness. This may present with functional limitations, such as difficulty getting up from
the floor, getting into and out of motor vehicles, or climbing stairs. Washing or grooming hair may
pose a challenge, and severely affected children may not be able to feed themselves. In very
young children, frequent falls may be an important symptom. A Gower's sign is frequently present.
Weakness of the palate and cricopharyngeal muscle may result in problems swallowing, a nasal
voice, tracheal aspiration, and reflux of food into the nasopharynx. Involvement of the upper
esophagus can lead to dysphagia for solids and liquids.
Arthritis — Non-erosive arthralgia and arthritis may be present at the time of diagnosis or during
the disease course [3,4,50] . Contractures may be seen but are usually related to muscle weakness
rather than arthritis.
Lipodystrophy — Acquired lipodystrophy (show picture 2, panel F) and associated metabolic
abnormalities such as insulin resistance, acanthosis nigricans, and type 2 diabetes are being
increasingly recognized in patients with JDM. In a study of 20 patients with JDM, 4 were found to
have lipodystrophy accompanied by either insulin resistance or type 2 diabetes, while an
additional 13 had glucose and lipid abnormalities without evidence of lipodystrophy  . In
another study of 20 patients, 13 patients had lipoatrophy based upon subcutaneous fat
quantification by skinfold caliper including 8 patients with physical findings of lipodystrophy  .
Oral glucose tests were normal in all patients, but 12 of 18 patients tested were found to have
JDM appears to be a common cause of lipodystrophy children. In a retrospective review, JDM
alone or in association with other autoimmune disease (eg, juvenile rheumatoid arthritis) was the
underlying disease in 18 of 23 children with acquired lipodystrophy. Other findings included
acanthosis nigricans (n = 5 patients), hyperpigmentation (n = 5), elevated liver enzymes (n = 5),
and hypertension (n =3)  .
Other findings — Other clinical manifestations of JDM include: Pulmonary involvement —
Pulmonary manifestations are much less common in children than adults, but interstitial lung
disease may occur  . Gastrointestinal vasculopathy — Gastrointestinal (GI) tract involvement is
relatively rare, but can be life-threatening. Affected patients may present with abdominal pain,
pneumatosis intestinalis, gastrointestinal bleeding, or perforation [2,55] . Acute GI vasculitis and
chronic abdominal endarteropathy have been described in patients with JDM, indicating that the
underlying pathology leading to ulceration and perforation of the intestines is complex  .
Any patient with JDM experiencing abdominal pain that persists or progresses warrants careful
investigation because GI vasculopathy may occur late in the disease course or in a patient with
only mild myositis. Of note, abdominal radiographs and stool testing for occult blood may be
normal in patients with GI involvement. The need for further investigation, such as abdominal
ultrasonography or computed tomography (CT), must be guided by clinical suspicion for significant
GI involvement. Anasarca — The presence of anasarca at presentation may be a poor prognostic
sign indicating severe disease that may respond very slowly to treatment and may not respond to
corticosteroids alone. The generalized edema may be the result of a diffuse capillary leak resulting
from vascular endothelial damage  .
SUMMARY — Juvenile dermatomyositis (JDM) and juvenile polymyositis (JPM) are rare
autoimmune myopathies affecting children. JDM is the most common of these disorders
accounting for 80 percent of cases with a reported incidence that range from two to four cases per
million children. (See "Epidemiology" above). Although the etiology of JDM and JPM remains
unclear, it has been proposed that these disorders are caused by an autoimmune reaction within
the muscle tissue of genetically susceptible individuals, possibly in response to environmental
triggers. (See "Pathogenesis" above). Symmetrical proximal muscle weakness is the hallmark
clinical feature of these two disorders. In addition, heliotrope rash (reddish-purple rash on the
upper eyelids, often accompanied by swelling of the eyelid, show picture 1) and Gottron's papules
(erythematous, papulosquamous eruption over the dorsal surfaces of the knuckles, show picture
1) are characteristic rashes of JDM. Children with JDM and JPM also may have constitutional
symptoms (fever, weight loss, fatigue, and headache), which may be the initial finding prior to the
onset of muscle weakness, and in patients with JDM, rash.
Other clinical manifestations include nailfold capillary changes, skin ulcerations, calcinosis (soft
tissue calcification), non-erosive arthalgia and arthritis, lipodystrophy, and insulin resistance (show
picture 2). Gastrointestinal vasculopathy is a relative rare, but life-threatening manifestation that
may present as abdominal pain, pneumatosis intestinalis, gastrointestinal bleeding, or perforation.
(See "Clinical manifestations" above).
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