Distinctive features of idiopathic inflammatory myopathies in French Canadians

This is the first report on idiopathic inflammatory myopathies (IIM) in French Canadians. We reviewed retrospectively 30 French Canadian adults (20 women and 10 men) with IIM seen consecutively over 12 years. The median age at diagnosis was 45 years. The IIM were 8 (27%) primary polymyositis (PM), 9 (30%) primary dermatomyositis (DM), 5 (17%) IIM with neoplasia (lymphoma, breast, esophageal, colonic, and skin cancer) and 8 (27%) IIM with a connective tissue disease (4 with systemic sclerosis, 2 with mixed connective tissue disease, and 2 with rheumatoid arthritis). The most common presenting symptom was proximal muscle weakness (n = 10,33%). Of the remaining 20 patients, 6 (20%) had the onset of their weakness within 1 month of the presenting symptom. Only 3 (10%) patients did not have proximal muscle weakness. Twenty-six (87%) patients had weakness in the pelvic girdle, 25 (83%) in the shoulder girdle, and 7 (23%) in the neck muscles. Other common symptoms included dyspnea on exertion and dysphagia, each present in 13 (43%) patients. Gottron's papules and the heliotrope rash were the most common skin lesions documented in 11 (37%) and 10 (33%) patients, respectively. The serum creatine kinase (CK) level was between 171 and 1,000 U/L in 13 (43%) patients and between 1,001 and 6,000 U/L in 13 (43%) patients. Antinuclear antibodies (ANA) on HEp-2 cells were positive in 16 (53%) patients, of which 2 (13%) expressed autoantibodies to nuclear pore complexes. Autoantibody specificities were anti-La (n = 4, 13%), anti-U1RNP (n = 3, 10%), and anti-Ro (n = 2, 7%). None of the patients expressed anti-Jo-1, anti-topoisomerase I, or anticentromere antibodies. Twenty-eight (93%) patients received corticosteroid therapy, and 8 (27%) patients responded to prednisone alone. Thirteen (43%) patients were treated with methotrexate, and 9 (69%) responded. The mean follow-up was 62 months: 23 (77%) had their disease controlled, 3 (10%) patients were lost to follow-up, and 4 (13%) died (no death occurred because of IIM or its treatment). Therapy was discontinued because of remission in 5 (17%) patients. Cumulative survival rates at 2, 5, and 10 years were 89%, 89%, and 85%, respectively. The presence of autoantibodies to nuclear pore complexes and anti-La autoantibodies, the rare occurrence of anti-Jo-1 autoantibodies, the response to conventional therapies, and a high survival rate may distinguish IIM in French Canadians from that of other reported series.