Using Myositis-Specific Antibodies to Identify Phenotypic Subgroups of Juvenile Dermatomyositis

Compared with children with P155/P140 antibody-negative juvenile dermatomyositis (JDM), those with the anti-P155/P140 subtype may have greater damage to the nailfold capillary system; however, P155/P140 may not be associated with greater frequency of generalized lipodystrophy, according to results of a report published in Arthritis Care & Research.

Authors of the report conducted a retrospective chart review study using medical records data obtained from a juvenile myositis treatment facility in Chicago. Children with a clinical diagnosis of JDM and at least 5 years of follow-up data were eligible for inclusion in the analysis. Dual-energy x-ray absorptiometry (DXA) was performed to assess body fat composition. Patients also underwent immunoprecipitation and immunodiffusion to measure the presence of myositis-specific antibodies (MSA). The primary outcome was lipodystrophy as determined by DXA results and clinician assessment. The relationship between anti-P155/140 status and damage to the nailfold capillary system was also examined.

A total of 96 patients with JDM were enrolled in the current analysis, among whom 78% were girls and 70% were White. Patients were divided into 3 groups based on MSA status: 42% anti-P155/150 antibody, 23% other MSA, and 35% MSA-negative. The diagnostic groups had similar composition by age, race, and sex. Disease activity was also not significantly different between groups. However, the duration of untreated disease was twice as long in the anti-P155/140 group compared to the other groups (P =.027). Overall, lipodystrophy was not more common in the anti-P155/140 group (33%) compared to the MSA group (24%) and MSA-negative group (34%; P =.697). Total body fat percentage and trunk-to-leg fat ratio were also similar between groups during follow-up. Compared to the MSA negative group, the anti-P155/140 group had lower nailfold capillary end-row loop count at initial assessment (P =.01). This difference persisted after adjustments for untreated disease duration.

While previous studies have suggested an association between anti-P155/140-positive autoantibodies and generalized lipodystrophy, the current analysis indicated that lipodystrophy may be prevalent among all MSA groups. However, the authors observed that patients with anti-P155/140-positive antibodies had greater nailfold capillary damage than patients without MSA.

Limitations included the relatively small cohort size and the use of DXA — rather than magnetic resonance imaging (MRI) or computed tomography (CT) scans — to assess body fat distribution. In addition, focal lipodystrophy was not examined, which may be more common among patients with anti-P155/140-positive antibodies.

“These findings suggest that the anti-P155/140 MSA subgroup may warrant the initiation of more aggressive therapy,” the authors wrote. “Further studies are needed to identify nailfold capillary changes relative to MSA subtype to determine if additional patterns exist, which may provide much needed aid to clinicians in making treatment decisions in this disease population.”

Reference

Khojah A, Liu V, Savani SI, et al. Studies of 96 children with juvenile dermatomyositis: P155/140, is associated with loss of nailfold capillaries, but not generalized lipodystrophy. Arthritis Care Res (Hoboken). Published online December 8, 2020. doi:10.1002/acr.24535