Pediatric emergency medicine trisk 742

introduction of potent immunomodulators earlier in the disease course has led to
improved outcomes. The mortality rate may now be as low as 1.5% in the United
States, and drug- and disease-related morbidity are also improving. Despite these
advances, however, JDM remains a serious disease that requires the care of physicians
experienced with its management.
While historically, Bohan and Peter’s criteria for DM/polymyositis (PM) in adults
had been used in children, a revised diagnostic and classification system was
introduced in 2017. The EULAR/ACR diagnostic and classification criteria are
intended to diagnose inflammatory myopathies in both children and adults. The system
is made up of several variables related to skin and muscle inflammation with different
scales depending on the presence or absence of muscle biopsy information ( Table
101.8 ). JDM differs from adult DM in several important features. There is a more
prominent degree of vascular inflammation, it less commonly involves detectable
autoantibodies, and it rarely accompanies malignancies. Further, in children, the
appearance on MRI is essentially diagnostic because other causes of inflamed muscle
and soft tissue are not seen in this age group ( Fig. 101.4 ).
Microscopically, the skin in JDM shows dermal atrophy, obliteration of appendages,
and lymphocytic infiltration. The muscle typically demonstrates a mixture of
degenerating and regenerating muscle fibers, variations in muscle fiber size,
perivascular lymphocytic infiltration, and perifascicular atrophy of muscle fibers. Small
arteries, venules, and capillaries of the skin, muscle, fat, and GI tract characteristically
reveal angiopathy. While the pathogenesis of JDM has not been clearly defined, there
are several models to explain its development including environmental triggers like
viral infections, particularly Coxsackie B; vasculitis caused by immune complex
deposition; and cell-mediated cytotoxicity directed against muscle fibers. Certain HLA
haplotypes, especially HLA-B8/DR3, may predispose to the disease. Synthesizing
these findings, JDM is thought to represent an as-yet unexplained perpetuation of
muscle inflammation in susceptible hosts following an exogenous trigger.

Clinical Considerations
Clinical Recognition

JDM has a wide clinical spectrum, from a mild form involving mainly the skin (JDM
sine myositis or amyopathic JDM) to a severe vasculitic type with a fulminant course.
When untreated, the natural history of JDM is to pass through four overlapping phases
that typically last for 2 to 5 years but may persist indefinitely: (i) A prodromal phase of
nonspecific aches and pains, (ii) a phase of progressive muscle and skin inflammation
characterized by weakness and rash, (iii) a phase of persistent active disease and
cumulative tissue damage, and (iv) an indolent phase with development of contractures
and calcinosis but minimal ongoing inflammation. The goal of therapy is to abort this
progression such that it ends before irreversible damage occurs.


The onset of JDM is often insidious, with aches and pains in the limbs, malaise, lowgrade fever, and edema of the hands, feet, and eyelids. There may be a diffuse and
nonspecific rash. This prodromal stage evolves into the acute phase, when the
characteristic features of JDM become evident. Classical skin manifestations include a
violaceous heliotrope rash in the periorbital region and occasionally on the forehead;
dusky red or atrophic lesions over the extensor aspects of the knees, elbows, and
knuckles (Gottron papules); and periungual erythema ( Fig. 101.5 ). Skin findings may
precede or follow the onset of muscle weakness. Ulcerative skin lesions and anasarca
are rare presenting manifestations of JDM associated with a particularly severe disease
course.
Muscular involvement in JDM is characterized by symmetric proximal muscle
weakness that may be accompanied by pain and tenderness. Strength of the anterior
neck flexors and abdominal muscles is particularly affected, while facial muscles are
spared. The disease may progress to involve the muscles of the palate and pharynx,
resulting in regurgitation, nasal voice, and aspiration. Weakness of the respiratory
muscles can lead to a poor cough, pneumonia, and respiratory failure. Risk of GI
hemorrhage and perforation are increased at this stage.
The clinical course of JDM is variable; however, with the newer approaches to
treatment, disease manifestations may be controlled within a few months in the vast
majority of patients. Children with ongoing muscle inflammation for more than 6 to 12

months are at risk of developing late complications of JDM. These include pronounced
muscle wasting, contractures, lipodystrophy, and pigmentary changes of the skin. The
rash over the extremities often becomes dry, scaly, and atrophic. Subcutaneous
calcifications historically have occurred in up to 30% of children during this phase,
although early aggressive treatment of inflammation dramatically reduces this rate.
Calcifications are most typically discrete nodules around large joints, but at times they
may take the form of a diffuse encasement of the soft tissues, known as calcinosis
universalis. Occasionally, children pass through the early stages insidiously and come
to the attention of physicians only when they develop contractures and calcinosis.
Clinical Assessment
Although skin and striated muscle are the primary targets of the inflammatory process
in JDM, typically other organ systems are also involved. Up to one-third of children
develop arthritis, which may be present at diagnosis or may develop months into the
disease process. The arthritis of JDM is generally nonerosive and often improves as the
primary disease is treated, although some children require specific therapy for arthritis.
Neurologic manifestations of JDM are extremely rare, but peripheral polyneuropathy,
seizures, psychosis, and one case of suspected brainstem vasculopathy have been
reported.


TABLE 101.8
THE EULAR/ACR CLASSIFICATION CRITERIA FOR ADULT AND
JUVENILE IDIOPATHIC INFLAMMATORY MYOPATHIES


When no better explanation for the symptoms and signs exists these
classification criteria can be used
Score points
Variable

Age of onset
Age of onset of first symptom
assumed to be related to the
disease ≥18 yrs and <40 yrs
Age of onset of first symptom
assumed to be related to the
disease ≥40 yrs
Muscle weakness
Objective symmetric weakness,
usually progressive, of the
proximal upper extremities

Without With Definition
muscle muscle
biopsy biopsy
1.3

1.5

2.1

2.2

0.7

0.7

Objective symmetric weakness,
usually progressive, of the
proximal lower extremities

0.8

0.5

Neck flexors are relatively
weaker than neck extensors

1.9

1.6

In the legs, proximal muscles
are relatively weaker than
distal muscles

0.9

1.2

18 ≤Age (years) at onset of first
symptom assumed to be
related to the disease <40
Age (years) at onset of first
symptom assumed to be
related to the disease ≥40
Weakness of proximal upper
extremities as defined by
manual muscle testing or
other objective strength

testing, which is present on
both sides and is usually
progressive over time
Weakness of proximal lower
extremities as defined by
manual muscle testing or
other objective strength
testing, which is present on
both sides and is usually
progressive over time
Muscle grades for neck flexors
are relatively lower than neck
extensors as defined by
manual muscle testing or
other objective strength
testing
Muscle grades for proximal
muscles in the legs are
relatively lower than distal
muscles in the legs as defined