From the Guidelines
Inflammatory necrotizing myopathy should be treated with high-dose corticosteroids, such as prednisone (0.5-1 mg/kg/day), as first-line therapy, along with a steroid-sparing agent like methotrexate, azathioprine, or mycophenolate mofetil, to reduce morbidity and mortality and improve quality of life. The treatment approach for inflammatory necrotizing myopathy involves immunosuppressive therapy to manage the autoimmune response and prevent further muscle damage. According to the study by 1, the initial treatment approach for adult patients with idiopathic inflammatory myopathies, including inflammatory necrotizing myopathy, involves high-dose corticosteroids concurrent with a steroid-sparing agent.
The study by 1 provides further guidance on the initial treatment approach, recommending prednisone at a dosage of 0.5 to 1 mg/kg per day, with a taper after 2 to 4 weeks depending on patient response, and concurrent administration of an immunosuppressive drug, such as methotrexate, azathioprine, or mycophenolate mofetil, as a steroid-sparing agent. Key points to consider in the treatment of inflammatory necrotizing myopathy include:
- High-dose corticosteroids as first-line therapy
- Addition of a steroid-sparing agent to reduce corticosteroid dosage and prevent long-term side effects
- Monitoring of muscle strength and creatine kinase levels to evaluate treatment response
- Consideration of intravenous immunoglobulin or rituximab in severe or refractory cases
- Importance of physical therapy to maintain muscle strength and function.
Overall, the goal of treatment is to reduce inflammation, prevent further muscle damage, and improve quality of life for patients with inflammatory necrotizing myopathy, and the approach should be tailored to the individual patient's needs and response to therapy, as suggested by 1 and 1.
From the Research
Definition and Characteristics of Inflammatory Necrotizing Myopathy
- Inflammatory necrotizing myopathy (IMNM) is a distinct subgroup of inflammatory myopathy characterized by myofiber necrosis with minimal inflammatory infiltrates on muscle biopsy, highly elevated creatine kinase levels, and infrequent extra-muscular involvement 2.
- IMNM can be divided into three subtypes based on autoantibody positivity: anti-3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) IMNM, anti-signal recognition particle (SRP) IMNM, and antibody negative IMNM 2.
- Autoantibody status in IMNM has considerable correlation with clinical phenotype, prognosis, and recommended choice of immunosuppressive agent 2.
Treatment Strategies for IMNM
- Patients with anti-HMGCR IMNM tend to respond well to intravenous immunoglobulin (IVIG), and IVIG monotherapy may be sufficient treatment for certain patients 2, 3.
- In anti-SRP IMNM, early rituximab is commonly favored 2.
- Prompt initiation of aggressive immunosuppression is often indicated, as both anti-SRP and anti-HMGCR IMNM can potentially cause debilitating weakness, and muscle atrophy and irreversible fatty replacement happen early in the disease course 2.
- Patients with IMNM frequently require combination therapy to achieve disease control, and have a high rate of relapse when tapering immunosuppression 2, 3.
Challenges in Managing IMNM
- The optimal treatment strategy for IMNM is currently unknown and wide practice variation exists in the management of this condition 3.
- Further studies are needed to guide the optimal management of these patients 3.
- Young age of onset is a poor prognostic factor, and IMNM can be severely disabling and often requires aggressive immunosuppression 2.
Diagnostic Approaches and Current Research
- Diagnostic approaches include the role of muscle MRI and antibodies targeting 3‑hydroxy-3-methylglutaryl-CoA reductase (HMGCR) and signal-recognition peptide (SRP) 4.
- There has been an impressive international research effort to understand and characterise this emerging condition, although much remains unknown 4.
- Significant advances in the field include the discovery of specific autoantibodies, increased understanding of the risk factors, clinical characteristics and treatment options owing to a wealth of observational studies, and the development of novel classification criteria 4.