Background/Purpose:   Clinically Amyopathic Juvenile Dermatomyositis (CAJDM) is a distinct clinical phenotype of JDM in which patients (pts) often have characteristic JDM rashes with little to no evidence of muscle involvement. Our purpose was to investigate features distinguishing CAJDM from JDM.

Methods:   Demographic, clinical, laboratory, and treatment data from 13 (10 hypo- and 3 amyopathic) pts meeting Sontheimer’s criteria for CAJDM and from 65 myositis autoantibody (MSA)-matched (1:5) JDM pts meeting probable or definite Bohan and Peter criteria were examined. Differences were evaluated by Fisher’s exact and Mann-Whitney tests and significant univariable results were examined in multivariable logistic regression. MSAs were tested by standard immunoprecipitation methods. Scores for each organ system were based on the number of signs/symptoms present at diagnosis vs. the number assessed.

Results:   Sixty-nine percent of CAJDM had anti-p155/140 Abs, 2 each (15.4%) had anti-MDA5 or were MSA negative. CAJDM more frequently had p155/150 Abs than the full cohort of 400 JDM (37.4% p155/140 Ab, p=0.038). CAJDM were younger at diagnosis vs. Ab-matched JDM (median 4.2 vs. 8.0 yrs, p=0.004). CAJDM tended to more often have a family history of autoimmune disease compared to JDM (83% vs. 48%, p=0.07). Gottron’s papules were most often the first rash in CAJDM (54% vs.14%, p=0.004) whereas combination of heliotrope and Gottron’s papules was most often the first rash in JDM (82% vs. 8%, p=0.0001). CAJDM more frequently had mild illness severity at onset (77% vs. 11%, p<0.0001). There were no differences in speed of disease onset, environmental factors preceding diagnosis, or median UV index scores (average and highest) based on residential location at time of diagnosis between the two groups. CAJDM less frequently had myalgias (7.7% vs. 63%, p=0.0004), arthralgias (15.4% vs. 56.9%, p=0.013), mucous membrane lesions (7.7% vs. 45%, p=0.012), calcinosis (0 vs. 35.4%, p=0.008), and fatigue (38.5% vs. 84.6%, p=0.0012) than JDM, and no ILD. The median muscle (0.0 vs. 0.29), skeletal (0 vs. 0.5) and overall (0.07 vs. 0.20) clinical symptom scores at diagnosis were lower in CAJDM than JDM (p≤0.001 for each). Muscle enzyme levels were less frequently increased in CAJDM (10-38% vs. 60-87%, p≤0.005); peak CK levels were lower (median 158 vs. 394 U/L, p=0.005) in CAJDM. CAJDM received less treatment, including fewer drug therapies (median 2 vs. 4, p=0.003) and treatment trials (median 2.5 vs. 5, p=0.004), had shorter durations on steroids (median 3.6 vs. 24 months, p=0.003), and less frequent use of prednisone (60% vs. 100%, p=0.0003). Multivariate logistic regression revealed a lower median muscle system score (p=0.009) was the only significant predictor of CAJDM compared to JDM. At a median f/up duration of 2.5 yrs, all CAJDM were ACR functional class I, 62% had rash, and none developed clinically significant muscle weakness or calcinosis vs. JDM (p ≤ 0.03).

Conclusion:  CAJDM may be distinguished from JDM in that they more likely have p155/140 Abs, are younger at diagnosis, have fewer clinical manifestations, especially muscle symptoms, lower muscle enzyme levels, receive less therapy including oral prednisone and have more favorable outcomes.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/features-distinguishing-clinically-hypo-and-amyopathic-juvenile-dermatomyositis-cajdm-from-juvenile-dermatomyositis-jdm/