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Introduction: The idiopathic inflammatory myopathies traditionally comprise dermatomyositis, polymyositis, immune-mediated necrotizing myopathy, anti-synthetase syndrome, and inclusion body myositis. In this review, we aimed to cover the less common forms of generalized myositis., Areas Covered: We identified rare forms of widespread myositis on the basis of list provided by the homepage of the Neuromuscular disease center of Washington University, USA and on the basis of the authors' knowledge. We searched PubMed® and EMBASE® for relevant articles on these forms with the aim of providing as much as possible information on their clinical manifestations as well as guidance on their work-up and treatment., Expert Opinion: There is substantial heterogeneity among the various rare forms of generalized myositis in terms of their frequency and characterization. Some forms are reasonably well defined, while others may not represent truly well-defined diseases, but rather variants of other myopathies. The landscape of rare forms appears to have evolved over time, with some forms now being better characterized, while others, such as SARS-Cov-2- and immune checkpoint inhibitor-related myositis have come to the fore only in recent years. Knowledge about rare forms of myositis can aid in their recognition and treatment.

Introduction: The idiopathic inflammatory myopathies traditionally comprise dermatomyositis, polymyositis, the anti-synthetase syndromes, immune-mediated necrotizing myopathy and inclusion body myositis. However, there are uncommon localized forms that are less known. In this review, we aimed to cover these uncommon forms., Areas Covered: We identified rare forms of localized myositis on the basis of list provided by the homepage of the Neuromuscular disease center of Washington University, USA and on the basis of the authors' knowledge. We searched PubMed® for relevant articles on these forms with the aim of providing as much as possible information on their clinical manifestations as well as guidance on their work-up and treatment., Expert Opinion: herein, we provide un updated description of rare forms of localized myositis. These forms are often difficult to diagnose because of their localized nature and are sometimes misdiagnosed as tumors. Knowledge about these rare forms of localized myositis can aid in their recognition and treatment.

The idiopathic inflammatory myopathies are chronic diseases of the skeletal muscle that comprise various conditions, including dermatomyositis, polymyositis, immune-mediated necrotizing myopathy, and the antisynthetase syndrome. Although there are a number of distinguishing features, all these disorders are characterized by an immune and inflammatory response mainly directed against the muscle. Hence, therapy is geared toward curbing the autoimmune and inflammatory response. A quite wide range of medications are currently available to treat these disorders, but despite all therapeutic progress still a number of patients are unable to maintain a sustained remission. In this review article, we have marshaled a variety of potential therapeutic agents that may hold promise for the future treatment of the idiopathic inflammatory myopathies. It is to be expected that by increasing the therapeutic armamentarium with agents that have different mechanisms of action even challenging cases could be successfully managed, thus reducing disease burden and disability., Competing Interests: Conflict of interest statement: The authors declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: IC: none. CG: none. CS: received consulting and investigator fees from Abbvie, Pfizer, MSD, Roche, Celgene, and Novartis. NP: Guest speaker at UCB-sponsored meetings: (Immunology Summits, Prague, 2012, 2013, & 2014, MACRO Meet the expert at the ACademy of RheumatOlogy, Bologna 13–14 April 2012, GRAPPA Workshop, Milan 29 January 2016 and Rome 30 November 2017), Fininvest (Catania 2016), Aim Group (Reggio Emilia 2018), I&C (Bologna, 2018), Alfa-Wassermann/Planning congressi sponsored meeting (Rhewind, Bologna, February 2016 and 2019). Received royalties from Uptodate.com and consultant fees from Janssen-Cilagin. Investigator in the CL2-78989-010 Servier study (2014) and the sirukumab in GCA GSK study (2016); PI for the ToReMy (Tocilizumab in Refractory Myositis) AIFA [Italian Drug Agency]-funded (2017) study and for the FOREUM-funded (2018) GCA study; investigator for the ADIENNE ADN016 study (2022)., (© The Author(s), 2022.)

Objectives: To define the clinical spectrum time-course and prognosis of non-Asian patients positive for anti-MDA5 antibodies., Methods: We conducted a multicentre, international, retrospective cohort study., Results: 149 anti-MDA5 positive patients (median onset age 53 years, median disease duration 18 months), mainly females (100, 67%), were included. Dermatomyositis (64, 43%) and amyopathic dermatomyositis (47, 31%), were the main diagnosis; 15 patients (10%) were classified as interstitial pneumonia with autoimmune features (IPAF) and 7 (5%) as rheumatoid arthritis. The main clinical findings observed were myositis (84, 56%), interstitial lung disease (ILD) (108, 78%), skin lesions (111, 74%), and arthritis (76, 51%). The onset of these manifestations was not concomitant in 74 cases (50%). Of note, 32 (21.5%) patients were admitted to the intensive care unit for rapidly progressive-ILD, which occurred in median 2 months from lung involvement detection, in the majority of cases (28, 19%) despite previous immunosuppressive treatment. One-third of patients (47, 32% each) was ANA and anti-ENA antibodies negative and a similar percentage was anti-Ro52 kDa antibodies positive. Non-specific interstitial pneumonia (65, 60%), organising pneumonia (23, 21%), and usual interstitial pneumonia-like pattern (14, 13%) were the main ILD patterns observed. Twenty-six patients died (17%), 19 (13%) had a rapidly progressive-ILD., Conclusions: The clinical spectrum of the anti-MDA5 antibodies-related disease is heterogeneous. Rapidly-progressive ILD deeply impacts the prognosis also in non-Asian patients, occurring early during the disease course. Anti-MDA5 antibody positivity should be considered even when baseline autoimmune screening is negative, anti-Ro52 kDa antibodies are positive, and radiology findings show a NSIP pattern.