Skip to content
How It Works
Explore
Resources Ask a Question
Who It's For
Patients
Decode results, prep for appointments, weigh options.
Caregivers & advocates
Carry the research load for someone you love.
Providers & clinicians
Resources for patients in your practice.
Log In Ask a Question
PubMed This is a summary of 27 peer-reviewed journal articles Updated
Neurology

The Biology of IMNM: Three Subtypes and How They Damage Muscle

At a Glance

Immune-Mediated Necrotizing Myopathy (IMNM) is divided into three subtypes: anti-SRP, anti-HMGCR (often triggered by statins), and seronegative (associated with higher cancer risk). Identifying your specific subtype is essential for guiding treatment and stopping muscle destruction.

Immune-Mediated Necrotizing Myopathy (IMNM) is not a single disease, but a group of conditions that share a common outcome: the immune system directly destroys muscle fibers (necrosis). To manage this condition effectively, doctors categorize it into three distinct subtypes based on the specific “attack proteins” (autoantibodies) found in your blood [1][2].

The Three Biological Subtypes

Knowing your subtype is critical because it helps predict how your disease might progress and which treatments may work best [3][4].

  1. Anti-SRP (Signal Recognition Particle): This is often the most aggressive subtype [5]. It typically causes rapid, severe muscle weakness and is more likely to involve areas outside the muscles, such as the heart or lungs [6][7]. It can be “treatment-refractory,” meaning it may require multiple powerful medications to bring under control [8].
  2. Anti-HMGCR (3-hydroxy-3-methylglutaryl-coenzyme A reductase): This subtype is frequently triggered by statin medications (used for cholesterol), though it can also occur in people who have never taken them [9][10]. Many patients with this subtype carry a specific genetic marker called HLA-DRB1*11:01 [11][12].
    • CRITICAL SAFETY WARNING: While statins are safe for the vast majority of people, they can trigger this condition in rare cases [9]. If you are diagnosed with or suspected of having anti-HMGCR IMNM, you must immediately contact your doctor to stop taking any statin medications. Continuing them will actively fuel the destruction of your muscles.
  3. Seronegative: If you have the hallmarks of IMNM on a biopsy but no antibodies are found in your blood, you are “seronegative” [13]. Patients in this group often experience muscle pain (myalgia) at the very beginning [13]. Importantly, this group has a higher risk of an underlying cancer (malignancy). Ruling out cancer is a day-one priority, not just a long-term monitoring task. Thorough and urgent cancer screening is mandatory [14][15].

How Your Muscles Are Damaged

In most other muscle diseases, the damage is caused by “wandering” immune cells that cause inflammation. In IMNM, the damage is more targeted and “cleaner” in a way that can be deceptive [16][17].

  • The “Hole-Punch” Effect: In the anti-SRP and anti-HMGCR subtypes, the immune system activates a process called the complement cascade. This leads to the deposition of the Membrane Attack Complex (C5b-9) on the surface of your muscle fibers [13][18]. Think of this complex as a tiny machine that punches holes in the muscle cell membrane, causing the cell to burst and die [13].
  • Necroptosis: Recent research has identified a second form of damage called necroptosis—a type of “programmed” cell death [19]. The muscle cell essentially receives a signal to self-destruct [19].
  • The Macrophage “Cleanup”: Because there is very little traditional inflammation, the main immune cells found in the muscle are macrophages [20][21]. Their job isn’t necessarily to attack, but to “eat” and clear away the dead muscle fibers left behind by the necroptosis and complement attack [17].

The Typical Patient Journey

The “biological journey” usually begins with a trigger—like a statin, a viral infection, or even a vaccination—that confuses the immune system in a genetically susceptible person [22][23][24]. Once the autoantibodies are produced, they begin the cycle of punching holes in muscle fibers [18][4]. As fibers die, they leak a protein called Creatine Kinase (CK) into the blood [25]. Doctors use these high CK levels as a “smoke detector” to see how much active muscle damage is occurring [25][23]. Regardless of the subtype, the goal of treatment is to “turn off” the production of these antibodies as quickly as possible to stop the cycle of necrosis [26][27].

Common questions in this guide

What are the three subtypes of IMNM?
IMNM is categorized into three subtypes based on the specific autoantibodies found in your blood: anti-SRP, anti-HMGCR, and seronegative. Knowing your exact subtype is crucial because it helps doctors predict how your disease might progress and which treatments will work best.
Can statin medications cause IMNM?
Yes, the anti-HMGCR subtype of IMNM is frequently triggered by statin medications, which are commonly used to lower cholesterol. If you are suspected of having this subtype, it is critical to contact your doctor immediately to safely stop taking any statin medications.
What does it mean if my IMNM is seronegative?
Seronegative means your muscle biopsy shows signs of IMNM, but no specific autoantibodies are present in your blood. Because this specific subtype carries a significantly higher risk of an underlying cancer, your doctor will prioritize urgent, comprehensive cancer screenings.
How exactly does IMNM damage my muscles?
Instead of general inflammation, IMNM uses a targeted attack called the complement cascade. This process deposits tiny complexes on your muscle fibers that act like machines punching holes in the cells, causing them to burst and die in a process called necrosis.
Why do doctors monitor my Creatine Kinase (CK) levels?
Creatine Kinase (CK) is a protein normally found inside your muscles. When IMNM punches holes in your muscle fibers and destroys them, CK leaks out into your blood, allowing doctors to measure these levels as a 'smoke detector' for active muscle damage.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Am I positive for anti-SRP, anti-HMGCR, or am I considered seronegative?
  2. 2.Since I am seronegative, have we performed a comprehensive cancer screening to rule out an underlying cause?
  3. 3.Do I carry the HLA-DRB1*11:01 genetic marker, and does that change my long-term outlook?
  4. 4.Based on my subtype, should we be monitoring my heart or lungs more closely for extra-muscular involvement?
  5. 5.Does my biopsy show evidence of 'necroptosis' or significant C5b-9 deposition?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (27)
  1. 1

    Immune-mediated necrotizing myopathy: clinical features and pathogenesis.

    Allenbach Y, Benveniste O, Stenzel W, Boyer O

    Nature reviews. Rheumatology 2020; (16(12)):689-701 doi:10.1038/s41584-020-00515-9.

    PMID: 33093664
  2. 2

    Integrated Diagnosis Project for Inflammatory Myopathies: An association between autoantibodies and muscle pathology.

    Suzuki S, Uruha A, Suzuki N, Nishino I

    Autoimmunity reviews 2017; (16(7)):693-700 doi:10.1016/j.autrev.2017.05.003.

    PMID: 28479486
  3. 3

    Myositis-specific autoantibodies, a cornerstone in immune-mediated necrotizing myopathy.

    Anquetil C, Boyer O, Wesner N, et al.

    Autoimmunity reviews 2019; (18(3)):223-230 doi:10.1016/j.autrev.2018.09.008.

    PMID: 30639649
  4. 4

    Longitudinal Course of Disease in a Large Cohort of Myositis Patients With Autoantibodies Recognizing the Signal Recognition Particle.

    Pinal-Fernandez I, Parks C, Werner JL, et al.

    Arthritis care & research 2017; (69(2)):263-270 doi:10.1002/acr.22920.

    PMID: 27111848
  5. 5

    Thigh muscle MRI in immune-mediated necrotising myopathy: extensive oedema, early muscle damage and role of anti-SRP autoantibodies as a marker of severity.

    Pinal-Fernandez I, Casal-Dominguez M, Carrino JA, et al.

    Annals of the rheumatic diseases 2017; (76(4)):681-687 doi:10.1136/annrheumdis-2016-210198.

    PMID: 27651398
  6. 6

    Anti-SRP immune-mediated necrotizing myopathy: A critical review of current concepts.

    Ma X, Bu BT

    Frontiers in immunology 2022; (13()):1019972 doi:10.3389/fimmu.2022.1019972.

    PMID: 36311711
  7. 7

    Cardiac and Respiratory Complications of Necrotizing Autoimmune Myopathy.

    Triplett J, Kassardjian CD, Liewluck T, et al.

    Mayo Clinic proceedings 2020; (95(10)):2144-2149 doi:10.1016/j.mayocp.2020.03.032.

    PMID: 32807522
  8. 8

    Anti-SRP Antibodies and Myocarditis in Systemic Sclerosis Overlap Syndrome with Immune-Mediated Necrotizing Myositis (IMNM).

    Alexandru C, Donisa A, Bobirca F, et al.

    Medicina (Kaunas, Lithuania) 2024; (60(11)) doi:10.3390/medicina60111756.

    PMID: 39596941
  9. 9

    Unveiling the Rare Complication: Statin-Induced Immune-Mediated Necrotizing Myopathy.

    Chowdhury FH, Mahneva O, Maharaj M, Marciales W

    The American journal of case reports 2023; (24()):e941387 doi:10.12659/AJCR.941387.

    PMID: 38087774
  10. 10

    The incidence of anti-HMGCR immune-mediated necrotizing myopathy: an Australian and UK retrospective multi-site cohort study.

    Khoo T, Tan E, Limaye V, et al.

    Rheumatology (Oxford, England) 2025; (64(9)):4995-5003 doi:10.1093/rheumatology/keaf238.

    PMID: 40347460
  11. 11

    Genetic Biomarkers for Statin-Induced Myopathy.

    Prieto-Peña D, Urriago-Gil JD, Ocejo-Vinyals G, et al.

    International journal of molecular sciences 2025; (26(22)) doi:10.3390/ijms262211144.

    PMID: 41303626
  12. 12

    Epidemiological and genetic features of anti-3‑hydroxy-3-methylglutaryl-CoA reductase necrotizing myopathy: Single-center experience and literature review.

    Prieto-Peña D, Ocejo-Vinyals JG, Mazariegos-Cano J, et al.

    European journal of internal medicine 2022; (101()):86-92 doi:10.1016/j.ejim.2022.04.017.

    PMID: 35487805
  13. 13

    The Clinicopathological Distinction Between Seropositive and Seronegative Immune-Mediated Necrotizing Myopathy in China.

    Ma X, Xu L, Ji S, et al.

    Frontiers in neurology 2021; (12()):670784 doi:10.3389/fneur.2021.670784.

    PMID: 34290662
  14. 14

    Paraneoplastic anti-SRP antibody positive immune-mediated necrotizing myopathy in a young female associated with lymphoma.

    Heugenhauser J, Pauli FD, Stockhammer G, et al.

    Journal of neuromuscular diseases 2025; (12(4)):567-574 doi:10.1177/22143602251327002.

    PMID: 40266663
  15. 15

    A case of anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase antibody-positive paraneoplastic necrotizing myopathy associated with advanced gastric cancer that responded to intravenous immunoglobulin therapy.

    Yamaguchi T, Matsunaga A, Ikawa M, et al.

    Rinsho shinkeigaku = Clinical neurology 2017; (57(3)):118-123 doi:10.5692/clinicalneurol.cn-000982.

    PMID: 28228619
  16. 16

    Statin-Induced Anti-HMGCR-Associated Myopathy.

    Basharat P, Lahouti AH, Paik JJ, et al.

    Journal of the American College of Cardiology 2016; (68(2)):234-5.

    PMID: 27386780
  17. 17

    Immune-mediated necrotizing myopathy: Unusual presentations of a treatable disease.

    Nicolau S, Milone M, Tracy JA, et al.

    Muscle & nerve 2021; (64(6)):734-739 doi:10.1002/mus.27435.

    PMID: 34617293
  18. 18

    Necrosis in anti-SRP+ and anti-HMGCR+myopathies: Role of autoantibodies and complement.

    Allenbach Y, Arouche-Delaperche L, Preusse C, et al.

    Neurology 2018; (90(6)):e507-e517 doi:10.1212/WNL.0000000000004923.

    PMID: 29330311
  19. 19

    Phospho-MLKL Upregulation in Immune-Mediated Necrotizing Myopathy: Implications for Disease Pathophysiology and Diagnosis.

    Gao M, Cheng N, Yue D, et al.

    Neuropathology : official journal of the Japanese Society of Neuropathology 2026; (46(1)):e70046 doi:10.1111/neup.70046.

    PMID: 41622430
  20. 20

    CD163+ macrophage density in perimysial connective tissue associated with prognosis in IMNM.

    Sun H, Wang ZY, Han Y, et al.

    Annals of clinical and translational neurology 2024; (11(5)):1267-1279 doi:10.1002/acn3.52065.

    PMID: 38651547
  21. 21

    Where are we moving in the classification of idiopathic inflammatory myopathies?

    Tanboon J, Uruha A, Stenzel W, Nishino I

    Current opinion in neurology 2020; (33(5)):590-603 doi:10.1097/WCO.0000000000000855.

    PMID: 32852298
  22. 22

    Diffuse Large B-cell Lymphoma Complicated with Anti-3-hydroxy-3-methylglutaryl-Coenzyme A Reductase Immune-mediated Necrotizing Myopathy.

    Tokunaga Y, Akiyama M, Nakano K, et al.

    Internal medicine (Tokyo, Japan) 2025; (64(4)):589-595 doi:10.2169/internalmedicine.3880-24.

    PMID: 38987186
  23. 23

    Immune-Mediated Necrotizing Myopathy With Anti-3-Hydroxy-3-Methylglutaryl-CoA Reductase (HMGCR) Antibodies Following Viral Infection and Without Association With Statin Use: A Case Report.

    Ferreira P, Dâmaso F, Anastácio M, et al.

    Cureus 2024; (16(9)):e70281 doi:10.7759/cureus.70281.

    PMID: 39463677
  24. 24

    Anti-HMGCR myopathy misdiagnosed as motor neuron disease and complicated with COVID-19 infection.

    Barp A, Velardo D, Ciscato P, et al.

    Neurological sciences : official journal of the Italian Neurological Society and of the Italian Society of Clinical Neurophysiology 2021; (42(5)):1679-1682 doi:10.1007/s10072-021-05146-w.

    PMID: 33646438
  25. 25

    [Two cases of statin-induced immune-mediated necrotizing myopathy].

    Safi T, Wagner H

    Lakartidningen 2021; (118()).

    PMID: 34861042
  26. 26

    Rituximab in the treatment of immune-mediated necrotizing myopathy: a review of case reports and case series.

    Xiong A, Yang G, Song Z, et al.

    Therapeutic advances in neurological disorders 2021; (14()):1756286421998918 doi:10.1177/1756286421998918.

    PMID: 33786066
  27. 27

    Treatment of refractory immune-mediated necrotizing myopathy with efgartigimod.

    Yang M, Yuan J, Wang Y, et al.

    Frontiers in immunology 2024; (15()):1447182 doi:10.3389/fimmu.2024.1447182.

    PMID: 39502686

This page is for informational purposes only and does not replace professional medical advice. Always consult your healthcare provider before stopping any medications like statins or if you suspect you have IMNM.

Get notified when new evidence is published on Immune-mediated necrotizing myopathy.

We monitor PubMed for new peer-reviewed studies on this topic and email a short summary when something meaningful changes.