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 17 peer-reviewed journal articles Updated
Neurology

Recognizing the Symptoms and Warning Signs of IMNM

At a Glance

The hallmark symptom of Immune-Mediated Necrotizing Myopathy (IMNM) is proximal muscle weakness affecting the hips, thighs, and shoulders. IMNM can also cause life-threatening complications in the heart, lungs, and swallowing muscles, or rhabdomyolysis, requiring prompt medical attention.

The most prominent sign of Immune-Mediated Necrotizing Myopathy (IMNM) is a specific type of weakness that affects the muscles closest to the center of your body. However, because this disease is systemic (affecting the whole body), it can cause symptoms that reach far beyond your arms and legs [1][2].

Proximal Muscle Weakness

The hallmark of IMNM is proximal muscle weakness, which typically affects the hips, thighs, shoulders, and upper arms [3][4]. You might first notice this as:

  • Difficulty rising from a chair or a toilet seat without using your hands [3].
  • A “waddling” gait or trouble climbing stairs [4].
  • Heaviness in the arms when brushing your hair or reaching for overhead cabinets [3].

This weakness is usually subacute, meaning it develops over weeks or a few months, though in some cases, it can be chronic and progress slowly over years [3][5].

Practical Tip: While you wait for treatments to begin working, practical daily accommodations are essential. Consider using raised toilet seats, avoiding low couches or deep chairs, and moving frequently-used kitchen items to waist-level counters.

Beyond the Muscles: Extramuscular Symptoms

While IMNM is primarily a muscle disease, it can affect other vital systems. These “extramuscular” symptoms are critical to monitor because they can be life-threatening [1][6].

  • Swallowing Difficulties (Dysphagia): The muscles used for swallowing can become weak, leading to dysphagia. This may cause you to cough while eating, feel like food is “stuck” in your throat, or experience changes in your voice [7][8].
  • Heart Involvement: In some patients, the immune system attacks the heart muscle. This can lead to arrhythmias (irregular heartbeats), palpitations, or cardiomyopathy (weakening of the heart muscle) [6][9].
  • Respiratory Issues: If the diaphragm or chest muscles weaken, you may feel short of breath (dyspnea), especially when lying flat [10][2]. In the anti-SRP subtype, there is also a risk of Interstitial Lung Disease (ILD), where the lung tissue itself becomes scarred [11][12].

The Role of Muscle Pain (Myalgia)

While some inflammatory muscle diseases are painless, many IMNM patients experience myalgia (muscle pain or soreness). Interestingly, patients who are seronegative (meaning no specific antibody was found in their blood) report muscle pain at the start of their illness more frequently than those with identified antibodies [13].

Common Misdiagnoses

Because IMNM can sometimes progress slowly, it is frequently mistaken for other conditions [14].

  • Muscular Dystrophy: IMNM is often confused with genetic conditions like Limb-Girdle Muscular Dystrophy (LGMD) or Facioscapulohumeral Muscular Dystrophy (FSHD) [15][14].
  • The Key Difference: A primary clue that the condition is IMNM rather than dystrophy is a dramatically elevated level of Creatine Kinase (CK)—a protein that leaks into the blood when muscles are actively dying [16][17].

Warning Signs to Watch For

If you experience any of the following, you should contact your medical team immediately:

  • Dark, tea-colored urine: This is a sign of a dangerous condition called rhabdomyolysis. The massive amount of dying muscle protein is overwhelming your kidneys. You must seek emergency care and stay highly hydrated [17].
  • Sudden or worsening shortness of breath [1].
  • Frequent choking or “going down the wrong pipe” while eating [7].
  • Fainting spells or a racing, irregular heartbeat [6].
  • A rapid drop in your ability to walk or move your arms [3].

Common questions in this guide

What are the earliest signs of IMNM?
The most common early sign of IMNM is proximal muscle weakness. Patients often notice difficulty standing up from a low chair, climbing stairs, or lifting their arms to brush their hair or reach high shelves.
Can IMNM affect organs other than my muscles?
Yes, because IMNM is a systemic disease, it can affect more than just your skeletal muscles. It can weaken swallowing muscles, cause irregular heartbeats, and lead to breathing difficulties or lung scarring.
Why is IMNM sometimes misdiagnosed as muscular dystrophy?
IMNM can cause muscle weakness that looks very similar to genetic muscular dystrophies, especially when it progresses slowly. Doctors can usually distinguish IMNM by looking for dramatically elevated Creatine Kinase (CK) levels in the blood, which indicate active muscle cell death.
Does IMNM cause muscle pain?
While some inflammatory muscle diseases are painless, many people with IMNM experience muscle pain or soreness, known as myalgia. This symptom is particularly common in patients who do not have a specific IMNM antibody identified in their blood.
What does dark or tea-colored urine mean if I have IMNM?
Dark or tea-colored urine is a critical warning sign of rhabdomyolysis, a condition where massive amounts of dying muscle protein overwhelm and damage the kidneys. If you notice this symptom, you must seek emergency medical care immediately.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Have we ruled out heart involvement with an EKG or echocardiogram, especially given the risks associated with IMNM?
  2. 2.Based on my symptoms and antibody status, should I have a baseline pulmonary function test (PFT) to check for lung involvement?
  3. 3.Could my symptoms be a 'mimic' of muscular dystrophy, and how does my biopsy confirm IMNM specifically?
  4. 4.If I have trouble swallowing (dysphagia), can you refer me for a formal swallowing study?
  5. 5.Is my current level of muscle pain (myalgia) typical for my specific subtype of IMNM?

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 (17)
  1. 1

    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
  2. 2

    Severe Anti-HMG-CoAR Necrotizing Autoimmune Myopathy Secondary to Statin Use.

    Pulipati P, Reddy JK, Husain SA

    Case reports in rheumatology 2022; (2022()):6120424 doi:10.1155/2022/6120424.

    PMID: 36158465
  3. 3

    Identical twins with statin-associated anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase autoantibody-positive autoimmune myopathy.

    Mali M, Pirilä L, Perander L, et al.

    Scandinavian journal of rheumatology 2024; (53(1)):81-82 doi:10.1080/03009742.2023.2289729.

    PMID: 38090763
  4. 4

    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
  5. 5

    Diagnostic modelling and therapeutic monitoring of immune-mediated necrotizing myopathy: role of electrical myotonia.

    Triplett JD, Shelly S, Livne G, et al.

    Brain communications 2020; (2(2)):fcaa191 doi:10.1093/braincomms/fcaa191.

    PMID: 33364599
  6. 6

    Necrotizing myopathy presenting as congestive heart failure and life-threatening ventricular arrhythmias: a case report.

    Lim K, Park JS, Yoon BA, Han SH

    European heart journal. Case reports 2021; (5(6)):ytab075 doi:10.1093/ehjcr/ytab075.

    PMID: 34142007
  7. 7

    A tough pill to swallow: Two cases of statin-induced necrotizing autoimmune myopathy manifesting as dysphagia and transaminitis.

    Chaudhry H, Lin J, Atefi R, et al.

    SAGE open medical case reports 2023; (11()):2050313X221150583 doi:10.1177/2050313X221150583.

    PMID: 36686203
  8. 8

    Anti-signal Recognition Particle Antibody-positive Necrotizing Myopathy with Secondary Cardiomyopathy: The First Myocardial Biopsy- and Multimodal Imaging-proven Case.

    Takeguchi-Kikuchi S, Hayasaka T, Katayama T, et al.

    Internal medicine (Tokyo, Japan) 2019; (58(21)):3189-3194 doi:10.2169/internalmedicine.2564-18.

    PMID: 31292376
  9. 9

    Evidence of Cardiac Involvement in a Patient With Necrotizing Autoimmune Myopathy (NAM).

    Khan OA, Wilches RM, Mehrabi JN, et al.

    Cureus 2023; (15(8)):e44106 doi:10.7759/cureus.44106.

    PMID: 37750137
  10. 10

    An Autopsy Case of Antibody-negative Immune-mediated Necrotizing Myopathy with Severe Cardiac Involvement.

    Tamura T, Miyajima K, Watanabe K, et al.

    Internal medicine (Tokyo, Japan) 2021; (60(19)):3113-3119 doi:10.2169/internalmedicine.6355-20.

    PMID: 33840691
  11. 11

    Anti-Signal Recognition Particle Antibody-Associated Severe Interstitial Lung Disease Requiring Lung Transplantation.

    Qureshi A, Brown D, Brent L

    Cureus 2020; (12(5)):e7962 doi:10.7759/cureus.7962.

    PMID: 32523819
  12. 12

    Overlap of Sjögren's Syndrome and Immune-Mediated Necrotizing Myopathy With Interstitial Lung Disease: A Case Report.

    Tanimura K, Omura S, Egami M, et al.

    Cureus 2024; (16(9)):e70385 doi:10.7759/cureus.70385.

    PMID: 39469393
  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

    Pediatric immune-mediated necrotizing myopathy.

    Wang CH, Liang WC

    Frontiers in neurology 2023; (14()):1123380 doi:10.3389/fneur.2023.1123380.

    PMID: 37021281
  15. 15

    Chronic Myopathy Associated With Anti-Signal Recognition Particle Antibodies Can Be Misdiagnosed As Facioscapulohumeral Muscular Dystrophy.

    Ikeda K, Mori-Yoshimura M, Yamamoto T, et al.

    Journal of clinical neuromuscular disease 2016; (17(4)):197-206 doi:10.1097/CND.0000000000000115.

    PMID: 27224434
  16. 16

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

    Safi T, Wagner H

    Lakartidningen 2021; (118()).

    PMID: 34861042
  17. 17

    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

This page provides educational information about the symptoms and warning signs of IMNM. It is not a substitute for professional medical advice, diagnosis, or emergency care.

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.