Background/Purpose: Granuloma in the muscle can be found in patients with myopathy. This finding has alternatively been interpreted as either sarcoid myopathy or other myositis subtype associated with granulomatosis. While the response of sarcoid myopathy to immunomodulatory therapy has been purported to be unpredictable, certain myositis subtypes have been linked to specific outcomes. Thus, we aimed at refining the predictive significance of granuloma in patients with myositis.

Methods: A group of 23 patients with myositis and granuloma on muscle biopsy (granuloma-myositis) from 8 centers (7 French and 1 Belgian), was analyzed and compared with a group of 23 patients without identified granuloma (control-myositis) randomly sampled in each centers.

Results: All but two granuloma-myositis patients had extra-muscular involvements, including sarcoid-like signs that were systematically absent in the control-myositis group, such as cutaneous granulomatosis (n=5) or ocular lesion (n=2). In addition, 52% of the granuloma-myositis patients group had biological signs of granulomatosis (i.e. hypercalcemia and/or increased angiotensin converting enzyme) vs. none in the control-myositis group.

Hardly half (43%) of the granuloma-myositis patients matched the ENMC 2013 diagnostic criteria for inclusion-body myositis (sIBM, clinico-pathologically defined: n=3, clinically defined n=4 and probable n=3), which was more frequent as compared with the control-myositis group. In accordance with sIBM diagnosis, as compared with remaining granuloma-myositis, these patients were more frequently men, with a longer delay between onset and diagnosis of myositis, suggesting a slow progression of the disease. However, all of them had also extra muscular involvements that were compatible with systemic granulomatosis. All patients were treated with corticosteroids (n=22), methotrexate (n=19), mycophenolate mofetil (n=5), intravenous immunoglobulins (n=3), anti-TNF drug (n=3), hydroxychloroquine (n=2), cyclophosphamide (n=2) because of suspicion of muscle sarcoidosis. Despite a higher number of immunomodulatory treatments as compared with the control-myositis group and the rest of granuloma-myositis group, only 1 granuloma-myositis patients matching ENMC 2013 criteria for sIBM reached muscle improvement (p<0.05 vs. the other myositis groups).

Aside one granuloma-myositis patient with anti-PM/Scl positive scleromyositis, the remaining 57% of granuloma-myositis patients did not match the criteria for a well-defined myositis subtype, suggesting pure sarcoidosis. The proportion of patients that reached the definition of muscle improvement at last follow-up in this group (69%) was not significantly different from the patients in the control-myositis group.

In multivariate analysis, matching criteria for inclusion-body myositis was the sole feature independently associated with non-response to myopathy treatment in patients with granuloma-myositis (p=0.003).

Conclusion: Granuloma-myositis patients should be carefully screened for inclusion body myositis, which is a very frequent condition in these patients, with important consequences for their care.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/granulomatous-myositis-heterogeneity-and-response-to-treatment/