Juvenile dermatomyositis

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3.2. What happens in JDM?

In JDM there is an alteration in the regulation of the immune system so that the patient's own organs and tissues are recognized as foreign and are "attacked" producing inflammation. This is known as systemic autoimmune disease, as opposed to organ-specific autoimmune diseases in which the autoimmunity affects only one organ or system.

In autoimmune diseases autoantibodies are detected in the blood, although the presence of these autoantibodies is not always the cause of the disease. Two types of autoantibodies are detected in JDM: myositis-specific antibodies, present almost exclusively in patients with inflammatory myopathies, and myositis-associated antibodies, present in patients with inflammatory myopathies and in patients with other connective tissue diseases (Table 1).

Table 1. Myositis-specific antibodies and myositis-associated antibodies.
Myositis-specific antibodies      Myositis-associated antibodies
Anti-Jo1 and other antisynthetases Anti-U1-, U2-, U3- y U5-RNP
Anti-Mi-2 Anti-PM-Scl
Anti-Signal Recognition Particle Anti-Ku
Anti-p155/140 (TIF - 1) Anti - Ro
Anti - MJ (NXP - 2) Anti - SUMO/RAE
Anti - CADM - 140 (MDA5) Anti - 43KD (cNIA)
Anti - 200/100 (HMG - CoA reductase)  

 

Some autoantibody is detected in approximately 70% of patients with JDM. Characteristically, in patients with inflammatory myopathies there is no overlap between the different types of autoantibodies. The myositis-specific antibodies most frequently found in JDM are anti-p-155 and anti-NXP2. The clinical manifestations of the patient vary according to the autoantibody detected (Table 2).

 

Table 2. Myopathy phenotype according to serological profile.
Anti-p155 (anti-TIFF-gamma) Severe skin disease, generalized lipodystrophy, chronic course of disease.
Anti-MJ (anti NXP2) They tend to have more weakness, more frequent GI involvement with bleeding and ulcers, and calcinosis. Only 8% of these patients will be in remission 2 years after starting immunosuppressive treatment.
Anti-MDA5 Less muscle involvement (hypomyopathic), interstitial lung disease and arthritis.
Anti-Mi2 Typical dermatomyositis rash. Unlike adults, they are not associated with shawl sign or cuticular hypertrophy.

 

Last modified
05 October 2023