AB0429 BELFAST TRUST EXPERIENCE OF IDIOPATHIC INFLAMMATORY MYOPATHIES
Authors: S. Loughrey, A. Herron, M. Mchenry, E. Ball
Journal: Annals of the Rheumatic Diseases (2021)

Background: The Idiopathic Inflammatory Myopathies (IIM) are a heterogeneous group of diseases where there is a growing field of knowledge and experience. Presentation is usually of onset of muscle weakness in combination with typical muscle biopsy findings and specific serum autoantibodies. There is a significant morbidity and mortality associated with IIM, due to its potential systemic nature, associated malignancy risk and side effects of immunosuppressive therapy1. There is no published guideline on management of IIM, with treatment limited to best practice experience. Objectives: Review Belfast Trust experience of Adult IIM from 2009-2020 Methods: Review of Electronic Records of 18 patients diagnosed with IIM between 2009-2020 Results: 18 patients diagnosed with IIM. Mean age at diagnosis is 64, with age range of 46-83. Mean duration of treatment is 4 years. 14 patients are in remission, 2 have active disease and 2 are deceased with cause of death unrelated to IIM. Muscle Biopsy was performed in 17 patients. 11 patients biopsies were diagnostic and 6 were supportive. Of the patients with DM who did not have diagnostic muscle biopsies, all 3 had diagnostic skin biopsies. Of 6 patients with a negative ANA, 5 had a muscle biopsy performed (diagnostic in 4 patients and supportive in 1 patient.) Table 1. Overview of diagnosis and treatment of patients with IIM. PM - Polymyositis DM - Dermatomyositis IBM - Inclusion Body Myositis IMNM Immune Mediated Necrotising Myositis EP - Extended Panel ILD - Interstitial Lung Disease RA - Rheumatoid Arthritis RTx - Rituximab IVIG - Intravenous Immunoglobulin MTx - Methotrexate AZA - Azathioprine MMF - Mycophenolate Mofetil SLZ - Sulphasalazine HLQ - Hydroxychloroquine Diagnosis ANA/Extramuscular Failed/Intolerance RTx IVIG Mtx AZA MMF Ciclos-porin SLZ/HLQ Prednisolone duration (months ) PM Jo-1 Ro AZA X 18 PM Jo-1 Myocarditis AZA x x x 12 PM Negative. No EP AZA/MMF/RTx x Maint. 3mg PM Negative. No EP ILD x 22 PM Jo-1 ILD, Mechanic Hands Mtx/MMF x x Maint. 7mg PM Negative. No EP x 36 PM Negative. No EP x 18, reducing dose PM Negative. No EP x x Maint. 5mg PM Ro ILD, Dysphagia x 6, reducing dose DM MDA5, Ro Rash, ILD AZA x x X 18 DM Mi2 Rash Mtx x X 20 DM PM-SCL Rash Deceased DM Ro52 Sicca x 6, reducing dose DM MDA5, NXP2 Rash x x Maint, 12.5mg DM- Amyopathic SAE Rash MTx x x X Deceased IBM Ro/La x x x Unknown duration. Now stopped IMNM HMGCR x 12 IMNM HMGCR x x x 18, reducing dose Conclusion: Extended myositis panels have only readily become available in the Belfast Trust in recent years. This has enhanced patients phenotypes and vigilance for extra-muscular complications. There is a recognised elevated risk of cancer in patients with IIM2. In our patients, with a mean disease duration of 4 years, none have developed malignancy. All of our patients had a tissue sample obtained, either muscle or skin. In the Belfast Trust, Rheumatologists perform muscle biopsies and all of the samples contributed to diagnosis. A limitation of diagnostic tests is restricted access to EMGs. We introduced a variety of DMARDs to limit exposure to steroids. 50% of our patients are in remission and off steroids. The only biologic we used was Rituximab. In contrast to other rheumatological conditions, there is no published protocol for administration of Rituximab in IIM. For patients with refractory disease, IVIG was used in the short term to allow for introduction of alternative immunosuppressants to maintain remission. This review highlights the complex nature of this group of diseases, and our experience with a variety of treatment options. We have diagnosed and treated 18 patients, and although we have experience with the medications used to treat IMM further work is needed to establish evidence based treatment. References: [1]Barsotti, Lundberg et al ‘Current Treatment for Myositis’ Curr Treatm Opt Rheumatol vol 4 (4) 2018 p299-315 2. Kang et al ‘Temporal relationship between cancer and myositis identifies two distinctive subgroups of cancers: impact on cancer risk and survival in patients with myositis’ Rheum vol 55 (9) 2016 p1631-1641 Disclosure of Interests: None declared