What is Necrotizing Autoimmune Myopathy (NAM)?

Simply Put

Necrotizing Autoimmune Myopathy (NAM) is considered to be an extremely rare neuromuscular autoimmune disease. The term “necrosis” is used medically to mean the death of the cells of an organ or tissue due to a disease, injury, or failure of the blood supply. (See the bottom section for important distinctions of necrosis)

NAM has symptoms similar to Polymyositis, impacting the proximal muscles such as thighs, quadriceps, shoulders, and neck. What sets the two diseases apart are the results of the NAM muscle biopsy, which tends to indicate muscle cell necrosis and regeneration without significant inflammation. While it indicates little or no inflammation, the creatine kinase (CK) level, an indicator of active muscle damage, is generally more than ten times that of normal levels.

The reason for the autoimmune response, which causes NAM, is not completely known, however, NAM cases have been reported as a result of drug therapy, especially statins used to control cholesterol, as well as cancer or connective tissue disease.

Signs & Symptoms of Necrotizing Autoimmune Myopathy

Necrotizing Autoimmune Myopathy affects the muscles closest to the body’s core such as thighs, quadriceps, shoulders, and neck. Onset of symptoms typically appears acutely or subacutely, which can be severe and can include:

  • Symmetrical muscle weakness, like that found with polymyositis and dermatomyositis. Weakness in other muscles, including breathing and swallowing muscles, has been found as well.
  • Inability or difficulty climbing stairs or getting into a car
  • Inability or difficulty rising from a seated position
  • Difficulty washing, combing or brushing ones hair, or raising arms to lift an item such as putting a plate in a cabinet
  • Dysphagia (trouble swallowing)
  • Fatigue
  • Muscle pain
  • Cancer (3 years before or after)

Diagnosing Necrotizing Autoimmune Myopathy

A physician experienced in autoimmune and/or neuromuscular diseases is often the type of physician recommended to diagnose and treat NAM. A quick and accurate diagnosis is important in order to start effective treatment as soon as possible. After a thorough medical exam and understanding of the patient’s medical history and symptoms, it is common to have some of the following tests conducted:

  • CK (CPK) levels are generally elevated that of ten times the normal.
  • HMGCR and SRP antibody testing (found in some, but not all). HMGCR is the enzyme targeted by statins, and it is suggested that statins may trigger NAM, many patients with NAM have never taken statin medications. Nevertheless, the presence of the antibodies and the response to immunotherapy support the autoimmune nature of NAM.
  • Weight loss due to Dysphagia
  • Anti Nuclear Antibodies (ANA) blood test to indicate if specific antibodies are present, which are frequently associated with this condition
  • EMG to look for inflammation in affected muscles
  • MRI which may detect any diffuse or patchy-like edema in the affected muscles
  • Muscle biopsy, which is considered the “gold standard” in diagnosing this condition, will show little to no inflammation as is found with myositis.  Shows myocyte necrosis and regeneration without significant inflammation.

Treatment for Necrotizing Autoimmune Myopathy

In the case of drug-mediated NAM, it was once thought that discontinuing the drug or treating the malignancy would eliminate symptoms of NAM within weeks or months, however, in recent years, it has become recognized that discontinuing the drug or eliminating the malignancy does not always eliminate symptoms, especially if it is autoimmune in nature. A standard course of treatment such as those used for Polymyositis, Dermatomyositis, and other autoimmune diseases is more effective in arresting the disease or minimizing its effects.

The patient should start to see improvement after several weeks of high-dose corticosteroids. The physician will likely conduct a follow up with both a physical exam to determine if muscle strength has improved as well as another CK blood test to check to see if the levels are lower.

Other treatments may include:

  • A combination of steroids and IVIG has been shown to work.
  • Corticosteroids such a Prednisone
  • Disease Modifying Anti-rheumatic Drugs (DMARDs), which suppress the immune system (Mycophenolate Mofetil, Azathioprine, Methotrexate)
  • Intravenous drugs: IVIG or Rituxan for refractory cases

Complications of Necrotizing Autoimmune Myopathy

A typical course of treatment may successfully treat the symptoms, however, as in other autoimmune disorders, the condition can be considered chronic and progressive causing:

  • Weight loss due to Dysphagia
  • Interstitial Lung Disease
  • Cardiac Disease

Statin-Induced Myopathy, Drug-Induced Myopathy

While necrotizing autoimmune myopathy can be triggered by certain drugs, like the statins, it differs from actual statin-induced myopathy which will improve over time once the offending drug is discontinued; usually over weeks to months. NAM does not improve once the drug is discontinued. It requires ongoing treatment.

The most severe adverse effect of statins is myotoxicity, in the form of myopathy, myalgia (pain), myositis or rhabdomyolysis.

Potentials for drug-related myopathies have been noted with statins, steroids, colchicine, cocaine, ipecac, alcohol, zidovudine, and D-penicillamine.

Important notes: It is important to differentiate that this article is specifically about Necrotizing Autoimmune Myopathy, an autoimmune disorder, which is NOT the same disease as the non-autoimmune conditions such as Necrotizing Myositis; a bacterial infection with none of the symptoms discussed for NAM and is often considered an emergency.

Necrosis is also a term used when describing the death of tissue such as bone or joints due to diminished blood flow, often caused by using medications such as corticosteroids. The term “necrosis” should not be confused with Necrotizing Autoimmune Myositis.

Simply Put

“Simply Put” is a service of Myositis Support and Understanding, to provide overviews of Myositis-related medical and scientific information in understandable language.

MSU volunteers, who have no medical background, read and analyze often-complicated medical information and present it in more simplified terms so that readers have a starting point for further investigation and consultation with healthcare providers. The information provided is not meant to be medical advice of any type.

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