Background Case reports and short series (n<7) suggested that granulomatosis may be found in various inflammatory myopathies (IM) subtypes [1] but the clinical significance of this association is unanswered.

Objectives To study clinical significance of granulomatosis in IM patients.

Methods Patients with non-caseating granuloma (muscle or other tissue) were first identified among a monocentric cohort of 291 patients diagnosed with IM. 20 rheumatology and internal medicine practitioners were also contacted by electronic letters and asked to report their observations. Clinical, biological, histological features and evolution were retrospectively studied using a standardized questionnaire and compared with a control group of 14 randomly selected patients suffering from IM without identified granulomatosis.

Results 14 IM patients with granulomatosis with a median follow-up of 77 months were included. Age at IM diagnostic was 54 years (16 to 70). Granuloma was identified 44 months before IM (23 years before to 4 after) in muscle (n=5), lymph node (n=5), skin (n=2), liver or spleen (n=1) tissues. Angiotensin converting enzyme amount was 114U/l (48 to 168).

7 patients (4 women, 57±14 years at IM diagnosis) were categorized as a defined IM subset because of typical histological and/or immunological features: antisynthetase syndromes (n=3), polymyositis (n=1), scleromyositis (n=1), dermatomyositis (n=1), inclusion body myositis (sIBM, n=1). These patients mostly presented with proximal weakness (n=6/7). Mean CK level was 780±390U/l. None had granumola in muscle biopsy. Extra-muscular involvements were arthralgia (n=4), interstitial pneumonia (n=4), mechanic's hand (n=1) and Raynaud's phenomenon (n=1). Patients received corticosteroids and meanly one another immunological drug (n DMARDs=1±0,8) with effectiveness except for the sIBM patient. None of these features was significantly different from the control group.

7 patients (4men, 54±12 years) did not met definitive criteria of a specific myopathy. As compared with the control group, they presented more often with distal weakness (n=3/7, p=0.002) and had lower CK level (260±56 vs. 2028±600U/l, p=0.006). Muscle biopsy most frequently revealed granuloma (n=5). Other lesions were endomyosial inflammatory cell infiltration (n=4), fibers atrophy (n=4), rimmed vacuoles (n=2). The patients experienced polyarthralgia (n=4), interstitial pneumonia (n=3), Raynaud (n=2). Despite a higher number of DMARDs as compared with the control group (2.7±0.4 vs. 1.3±0.2, p<0.05) and the patients with granolumatosis and defined IM (p<0.05), absence of muscle improvement was more frequent (n=5/7).

Conclusions Half of IM patients with granulomatosis match diagnostic criteria for IM subtypes without clinical particularity aside from the granuloma. The unclassified others patients are characterized by an sIBM-like phenotype with distal weakness, low CK level and frequent unfavorable response to immunomoduling therapy despite not meeting criteria for definite sIBM. Clinicians should pay attention to auto-antibodies and muscle histology to tailor the care of IM patients with granulomatosis, which do not represent a homogeneous group.

1. Kenji Sakai,“Inclusion Body Myositis with Granuloma Formation in Muscle Tissue”, Neuromuscular Disorders no9 (Sept 2015): 706–12.

Disclosure of Interest None declared