(Albany, US), October 24, 2026 – DelveInsight’s ‘Idiopathic Inflammatory Myositis Market Insights, Epidemiology and Market Forecast – 2036’ report delivers an in-depth understanding of Idiopathic Inflammatory Myositis, historical and forecasted epidemiology, as well as the Idiopathic Inflammatory Myositis market trends in the United States, EU4 (Germany, Spain, Italy, and France), the United Kingdom, and Japan.
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Key Takeaways from the Idiopathic Inflammatory Myositis Market Report
In June 2026, Argenx presented new data on efgartigimod at EULAR 2026, demonstrating sustained long-term patient benefits in myositis.
Priovant announced that the US Food and Drug Administration (FDA) had accepted its New Drug Application (NDA) for brepocitinib for the treatment of dermatomyositis under Priority Review, with a US launch anticipated by the end of September 2026.
According to DelveInsight’s analysis, the IIM market size was nearly USD 470 million in the 7MM in 2025.
Across the 7MM, the United States represents the largest IIM market with approximately USD 280 million, accounting for the majority of IIM cases in 2025 and expected to maintain its leading position through 2036.
The IIM market is projected to grow at a CAGR of ~20% during 2026-2036.
According to DelveInsight’s analysis, the total diagnosed prevalent cases of IIM in the 7MM were approximately 200,000 cases in 2025.
Diagnosing IIM is challenging, particularly in the early stages when symptoms are nonspecific, and no uniform diagnostic criteria are available. Existing criteria, such as the Bohan and Peter criteria for dermatomyositis, rely on clinical, laboratory, and histopathological features that can be subjective and lack sensitivity and specificity.
The current therapeutic landscape in IIM includes corticosteroids, immunoglobulins such as intravenous immune globulin [Human] (OCTAGAM 10%), immunosuppressants like methotrexate, mycophenolate, and azathioprine, and biologics, including rituximab, abatacept, and TNF inhibitors.
There is a substantial need for new, effective, and convenient therapeutics addressing the underlying pathophysiology of IIM and its subtypes, along with comprehensive strategies to manage disease recurrence and minimize treatment-related complications.
The leading Idiopathic Inflammatory Myositis Companies include Priovant Therapeutics, Pfizer, Argenx, Amgen, and others.
Promising Idiopathic Inflammatory Myositis Therapies include Brepocitinib, Efgartigimod, Daxdilimab, and others.
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Idiopathic Inflammatory Myositis Overview
Myositis is a rare group of autoimmune inflammatory muscle diseases characterized by muscle inflammation that can also affect other organs, leading to significant impairment in quality of life. It is most commonly associated with the IIMs, which include polymyositis, dermatomyositis, juvenile dermatomyositis, cancer-associated myositis, overlap myositis, necrotizing autoimmune myopathy (NAM), and inclusion body myositis (IBM). In contrast, myopathy is a broader term encompassing any muscle disease, including inflammatory and non-inflammatory conditions. Among the inflammatory myopathies, dermatomyositis and polymyositis are the most common, although the classification of these disorders continues to evolve as new subtypes are identified. Diagnosing myopathies involves laboratory evaluation, imaging studies, multidisciplinary consultations, histologic examination, and potentially genetic studies. Testing for a patient with muscle weakness should include a thorough history and physical examination, routine laboratory tests (complete blood count, complete metabolic panel, muscle enzymes, thyroid-stimulating hormone, and other targeted studies as necessary), autoimmune serologies, imaging studies, neurologic evaluation, EMG, nerve conduction velocities, and muscle biopsy.
Idiopathic Inflammatory Myositis Epidemiology Segmentation in the 7MM
Total Diagnosed Prevalent Cases of Idiopathic Inflammatory Myositis
Type-specific Diagnosed Prevalent Cases of Idiopathic Inflammatory Myositis
Gender-specific Diagnosed Prevalent Cases of Idiopathic Inflammatory Myositis
Age-specific Diagnosed Prevalent Cases of Idiopathic Inflammatory Myositis
Treated Cases of Idiopathic Inflammatory Myositis
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Idiopathic Inflammatory Myositis Epidemiology Key Findings
The US had the highest number of diagnosed prevalent cases of IIM in 2025, with approximately 95,000 cases.
Among EU4 and the UK, Germany had the highest number of diagnosed prevalent cases of IIM with more than 22,000 cases in 2025, followed by France with around 18,000 cases and Italy with more than 15,000 cases.
Japan recorded approximately 27,000 diagnosed prevalent cases of IIM in 2025, with this number projected to rise by 2036.
In 2025, among the type-specific diagnosed prevalent cases of IIM in the US, polymyositis accounted for approximately 32,000 cases, dermatomyositis for around 40,000 cases, and IBM for nearly 23,000 cases.
Approved Therapies for Idiopathic Inflammatory Myositis
Intravenous Immune Globulin [Human] (OCTAGAM 10%), manufactured by Octapharma and distributed by Pfizer, is a liquid medication containing Immunoglobulin G (IgG) derived from human plasma donated by healthy individuals. It is approved for treating dermatomyositis in adults and is administered intravenously in hospitals, infusion centers, or at home, helping improve muscle function and reduce skin rashes. The US FDA approved OCTAGAM 10% for adult dermatomyositis in July 2021, and the European Union approved it in June 2021, followed by national approval in Germany in May 2021. In Japan, VENOGLOBULIN-IH 5% IV (Mitsubishi Tanabe Pharma) has been marketed for dermatomyositis and polymyositis since 2010.
Idiopathic Inflammatory Myositis Pipeline Analysis
Brepocitinib: Priovant Therapeutics/Pfizer
Brepocitinib is an oral drug that selectively inhibits the tyrosine kinases TYK2 and JAK1, which play roles in immune response and inflammation. By blocking these enzymes, brepocitinib disrupts inflammatory cytokine signaling, potentially reducing inflammation and preventing damage in various immunological diseases. The therapy is in Phase III development for dermatomyositis. Priovant announced that its New Drug Application (NDA) for brepocitinib in dermatomyositis had been accepted by the FDA for Priority Review and that it expected to launch the drug in the United States by the end of September 2026. Brepocitinib is expected to launch by 2026 with a medium-fast uptake.
Efgartigimod: Argenx
Efgartigimod is a first-in-class investigational antibody fragment designed to target the neonatal FcRn. It is being evaluated in a Phase III study for IIM as a subcutaneous therapy for patients with severe autoimmune diseases with the confirmed presence of pathogenic IgG autoantibodies where a severe unmet medical need exists. In June 2026, Argenx presented new efgartigimod data showing long-term sustained patient benefit in myositis at EULAR 2026.
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Idiopathic Inflammatory Myositis Market Outlook
Treatment of IIM is centered on controlling immune-mediated inflammation, improving muscle strength and physical function, preventing irreversible organ damage, and minimizing disease flares. Management typically requires a multidisciplinary approach involving rheumatologists, neurologists, dermatologists, pulmonologists, physiotherapists, rehabilitation specialists, and other healthcare professionals, depending on the extent of multisystem involvement. According to DelveInsight’s analysis, the total market size of the United States was approximately USD 280 million in 2025. Corticosteroids, including glucocorticoids with or without immunosuppressants, are the initial treatment in both first-line and refractory cases and have a significantly large patient pool. However, this does not translate into high revenue, with corticosteroids generating approximately USD 20 million in 2025. Immunoglobulin therapy has become an important treatment option, particularly for dermatomyositis, immune-mediated necrotizing myopathy, and refractory polymyositis, exerting multiple immunomodulatory effects by neutralizing pathogenic autoantibodies, inhibiting complement activation, modulating Fc receptor function, and regulating inflammatory cytokines. The pivotal ProDERM study of OCTAGAM 10% demonstrated significant improvements in disease activity and muscle function compared with placebo.
Idiopathic Inflammatory Myositis Treatment Landscape
Management of IIM is centered on immunosuppressive therapy. Glucocorticoids remain the first-line treatment, with intravenous methylprednisolone used in severe cases. Steroid-sparing agents such as methotrexate and azathioprine are commonly employed for long-term disease control, while mycophenolate mofetil, calcineurin inhibitors (cyclosporine and tacrolimus), and cyclophosphamide are used in refractory disease or in patients with myositis-associated interstitial lung disease (ILD). Intravenous immunoglobulin (IVIG), rituximab, ACTH gel, and hydroxychloroquine (primarily for cutaneous dermatomyositis) provide additional options depending on disease severity and clinical manifestations. Supportive care, including structured physical therapy and regular aerobic and resistance exercise, plays a vital role in improving muscle strength, functional capacity, and quality of life without exacerbating disease activity.
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Scope of the Idiopathic Inflammatory Myositis Market Report
Coverage- 7MM
Study Period- 2022-2036
Forecast Period- 2026-2036
Idiopathic Inflammatory Myositis Companies- Priovant Therapeutics, Pfizer, Argenx, Amgen, and others.
Idiopathic Inflammatory Myositis Therapies- Brepocitinib, Efgartigimod, Daxdilimab, and others.
Idiopathic Inflammatory Myositis Market Dynamics: Idiopathic Inflammatory Myositis market drivers and market barriers
Idiopathic Inflammatory Myositis Competitive Intelligence Analysis: SWOT Analysis, Attribute Analysis
Idiopathic Inflammatory Myositis Unmet Needs, KOL Views, Reimbursement
Table of Contents
Key Insights
Report Introduction
Market Overview at a Glance
Epidemiology and Market Forecast Methodology
Executive Summary
Key Events
Disease Background and Overview
Patient Journey
Epidemiology and Patient Population
Marketed Drugs
Emerging Drugs
Idiopathic Inflammatory Myositis: Market Analysis
Key Opinion Leaders’ Views
SWOT Analysis
Unmet Needs
Market Access and Reimbursement
Appendix
DelveInsight Capabilities
Disclaimer
About DelveInsight
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