Background/Purpose:

Myositis specific antibodies (MSA) can divide dermatomyositis patients into distinct clinical subsets and help predict the risk of disease complications such as interstitial lung disease and malignancy. Anti-NXP2 antibodies are one of the commonest MSA found in juvenile dermatomyositis (JDM) and can be identified in 18-25% cases. They have been associated with calcinosis and a severe disease course with more persistent disease activity. Anti-NXP2 antibodies have been found in adult myositis cohorts at a much lower frequency of 1.6%. A possible association with malignancy has been described in adults.

In this study we identified anti-NXP2 antibodies in a cohort of 172 juvenile and 1331 adult patients with idiopathic inflammatory myopathy and compared the clinical disease characteristics of both groups.

Methods:

Serum samples were obtained from EuMyoNet and UK JDRG repositories. Immunoprecipitation of radio-labelled K562 cells was performed on all samples. Those with a band in the 140kDa region were further assessed by western blot using an NXP2 overexpression cell lysate (Abnova).

Results:

Anti-NXP2 antibodies were identified in 20 children (11.6%) and 10 adults (0.8%). All children with anti-NXP2 antibodies had dermatomyositis. There was a strong association with calcinosis in children which was seen in 55% (p<0.0009). Of the adults nine had dermatomyositis and one polymyositis. One adult patient had calcinosis. An additional diagnosis of malignancy was present in three adults (breast, uterine, pancreatic) (p=0.051). When patients with anti-TIF1γ antibodies, (which are already known to be strongly associated with malignancy) were excluded this association became statistically significant (p=0.027).

Conclusion:

Anti-NXP2 antibodies are associated with an increased frequency of calcinosis in JDM. Calcinosis is a common cause of morbidity in JDM but is rarely seen in adult disease. It is interesting therefore that one adult patient with anti-NXP2 antibodies also had calcinosis. In JDM calcinosis is associated with delayed diagnosis, a chronic disease course and inadequately treated disease. Anti-NXP2 in JDM have previously been shown to be associated with a more severe disease course with worse functional status and persistent disease activity. The increased risk of calcinosis may therefore reflect more aggressive disease in anti-NXP2 positive children.

Consistent with previous findings there is an association with malignancy in our anti-NXP2 positive adult population. Whilst malignancy in JDM is rarely seen it is an important disease association in adults and associated with a poorer prognosis. Identification of anti-NXP2 in adult myositis patients may have important prognostic implications, particularly in older adults and should warrant a high level of suspicion for additional malignant disease. Whilst the same MSA are found in adult and juvenile dermatomyositis and define clinical subsets, important clinical differences are seen depending on patient age. Whether this reflects differences in aetiology, pathogenesis or age-specific disease modifiers is yet to be established.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/clinical-differences-between-adult-and-juvenile-dermatomyositis-associated-with-anti-nxp2-autoantibodies/