The Clinical Phenotypes of the Juvenile Idiopathic Inflammatory Myopathies

Abstract

The juvenile idiopathic inflammatory myopathies (JIIM) are systemic autoimmune diseases characterized by skeletal muscle weakness, characteristic rashes, and other systemic features. Although juvenile dermatomyositis (JDM), the most common form of JIIM, has been well studied, the other major clinical subgroups of JIIM, including juvenile polymyositis (JPM) and juvenile myositis overlapping with another autoimmune or connective tissue disease (JCTM), have not been well characterized, and their similarity to the adult clinical subgroups is unknown. We enrolled 436 patients with JIIM, including 354 classified as JDM, 33 as JPM, and 49 as JCTM, in a nationwide registry study. The aim of the study was to compare demographics; clinical features; laboratory measures, including myositis autoantibodies; and outcomes among these clinical subgroups, as well as with published data on adult patients with idiopathic inflammatory myopathies (IIM) enrolled in a separate natural history study.We used random forest classification and logistic regression modeling to compare clinical subgroups, following univariate analysis. JDM was characterized by typical rashes, including Gottron papules, heliotrope rash, malar rash, periungual capillary changes, and other photosensitive and vasculopathic skin rashes. JPM was characterized by more severe weakness, higher creatine kinase levels, falling episodes, and more frequent cardiac disease. JCTM had more frequent interstitial lung disease, Raynaud phenomenon, arthralgia, and malar rash. Differences in autoantibody frequency were also evident, with anti-p155/140, anti-MJ, and anti-Mi-2 seen more frequently in patients with JDM, anti-signal recognition particle and anti-Jo-1 in JPM, and anti-U1-RNP, PM-Scl, and other myositis-associated autoantibodies more commonly present in JCTM. Mortality was highest in patients with JCTM, whereas hospitalizations and wheelchair use were highest in JPM patients. Several demographic and clinical features were shared between juvenile and adult IIM subgroups. However, JDM and JPM patients had a lower frequency of interstitial lung disease, Raynaud phenomenon, “mechanic’s hands” and carpal tunnel syndrome, and lower mortality than their adult counterparts. We conclude that juvenile myositis is a heterogeneous group of illnesses with distinct clinical subgroups, defined by varying clinical and demographic characteristics, laboratory features, and outcomes.

Idiopathic inflammatory myopathies and the lung

“…ILD occurs after the diagnosis of polymyositis or dermatomyositis in up to 40% of patients, and precedes the diagnosis of overt CTD in 20-30% of cases [47,52]. In large cohorts of JDM/JPM, ILD occurs in 8-13% of patients and thus seems to occur less frequently than in adult dermatomyositis [53,54]. Risk factors for ILD in a patient with dermatomyositis/polymyositis include genetic predisposition [55,56], some clinical signs such as arthralgia [47], and autoimmune features (table 2) [22,56,57].…”

Idiopathic Inflammatory Myopathies: an Update on Classification and Treatment with Special Focus on Juvenile Forms

“…MAAs, such as anti-U1RNP, anti-Ro, anti-PM-Scl and anti-Ku autoantibodies, are found in up to 15 % of patients with JIIM, but are more frequently identified in patients suffering from overlap myositis [26,27].…”

“…This subgroup seems to suffer from a mild disease course [6]. Table 1 summarises the most frequent MSAs and MAAs, their frequencies and clinical associations [6,[17][18][19][20][21][22][23][24][25][26][27][28][29].…”

Four Cases of Anti-PM/Scl Antibody-positive Juvenile Overlap Syndrome with Features of Myositis and Systemic Sclerosis

“…Relatively few cases of childhood SSc/myositis overlap have been reported 1,2,3,4,5,6,7 . In our case series, 4 patients diagnosed with juvenile overlap syndrome of myositis with SSc are described ( Table 1).…”