Autoimmune Muscle Diseases

Introduction

Dermatomyositis (DM), immune-mediated necrotizing myopathy (IMNM), polymyositis (PM), inclusion body myositis (IBM), and myositis associated with the antisynthetase syndrome (ASS) comprise the autoimmune myopathies.1 These disorders, which afflict women about twice as often as males, are uncommon, with an estimated incidence of 4 cases per 100,000 person-years and a frequency of 15 to 32 cases per 100,000 [2]. Each disease subtype is linked with unique clinical, histopathologic, as well as pathophysiologic characteristics. Autoimmune myopathy patients often appear with progressive symmetric proximal muscle weakening over weeks or months.

Autoimmune disease

A functioning immune system protects the body against infection and illness. However, when the immune system fails, healthy cells, tissues, and even organs are wrongly attacked. These assaults, known as autoimmune illnesses, may damage any organ of the body, impairing basic function and even becoming life-threatening. Autoimmune illness occurs when the body's natural defence system is unable to distinguish between its own cells and foreign ones, leading it to erroneously target healthy cells. There are about eighty different forms of autoimmune disorders that affect a broad variety of bodily components. These are the most prevalent autoimmune disorders in women: 

  • Rheumatoid arthritis (RA) is a joint-attacking kind of disease 
  • Psoriasis is a skin disorder characterised by thick, scaly patches 
  • Psoriatic arthritis is a kind of arthritis that affects certain psoriasis patients 
  • Lupus is a disease that causes damage to joints, skin, and internal organs 
  • Thyroid illnesses include Graves' disease, in which the body produces much more thyroid hormone (hyperthyroidism), and Hashimoto's thyroiditis, in which it produces insufficient amounts (hypothyroidism)

Symptoms of autoimmunity may be severe in some individuals and modest in others. Additionally, the diagnosis might be challenging since similar symptoms can be caused by other prevalent illnesses. Despite the variety of autoimmunity types, many exhibit common symptoms. Common autoimmune disease symptoms include: 

  • Fatigue
  • Joint pain and inflammation 
  • Skin problems
  • Abdominal discomfort or digestive problems 
  • Persistent fever 
  • Swollen glands 

Researchers are unsure what triggers autoimmune illness, although various hypotheses include an overactive immune system that attacks the host body after an infection or damage. We do know that some risk factors, such as those listed below, enhance the likelihood of developing autoimmune illnesses. 

  • Certain diseases, like lupus and multiple sclerosis (MS), tend to run in families due to genetics. Having a family with an autoimmune illness raises the overall risk, but this does not guarantee that you will also get one. 
  • Becoming overweight or obese increases the likelihood of getting RA or psoriatic arthritis. This may be due to the fact that excess weight places a higher strain on the joints or because fat tissue produces compounds that promote inflammation. 
  • Numerous autoimmune illnesses, including lupus, RA, hyperthyroidism, and MS, have been related to smoking. 
  • Certain blood pressure drugs or antibiotics may cause drug-induced lupus, which is often a milder form of the disease. Orban’s myositis centre also revealed that some cholesterol-lowering drugs, known as statins, may cause statin-induced myopathy.

Autoimmune muscle diseases

Myositis, generalised muscle inflammation, may be caused by the following: autoimmune disorders in which the immune system attacks muscle; an allergic reaction following exposure to a toxic substance or medication; a virus or other infectious organisms such as bacteria or fungi; or a combination of these factors. The majority of inflammatory myopathies are regarded as autoimmune illnesses, in which the body's immune response system, which typically fights against infection and disease, targets the body's own muscle fibres, blood vessels, connective tissue, organs, and joints. Inflammatory myopathies are uncommon and may affect both children and adults. Dermatomyositis is the most prevalent type of chronic childhood disease. Polymyositis and dermatomyositis are more prevalent in women, but inclusion body myositis is more prevalent in men. Inclusion body myositis often affects people over the age of 50. The diagnosis is based on the patient's medical history, the outcomes of a physical examination that includes muscular strength tests, and blood samples that demonstrate high levels of certain muscle enzymes and autoantibodies. Tools for diagnosis include: 

  • Electromyography to capture the electrical activity of muscles during contraction and rest Ultrasound to detect muscle inflammation 
  • Magnetic resonance imaging to detect aberrant muscle anatomy 
  • Biopsy samples of muscle tissue should be evaluated for evidence of chronic inflammation, muscle fibre loss, vascular abnormalities, and other alterations that are unique to the diagnosis of a certain kind of inflammatory myopathy. A skin biopsy may reveal skin abnormalities caused by dermatomyositis

The majority of individuals with chronic inflammatory myopathies cannot be cured, however, several symptoms may be addressed. Medication, physical therapy, exercise, heat treatment, orthotics, and assistive gadgets are among the options. Dermatomyositis, polymyositis, and necrotizing autoimmune myopathy are first treated with corticosteroid medications such as prednisone in large doses. This is often administered orally, but may also be administered intravenously. In those who do not react well to prednisone, immunosuppressive medications such as azathioprine and methotrexate may decrease inflammation. Individuals with dermatomyositis, polymyositis, or NAM who get periodic intravenous immunoglobulin therapy have a greater probability of recovery. The inflammation associated with dermatomyositis and polymyositis may also be treated with cyclosporine A, cyclophosphamide, mycophenolate mofetil, and tacrolimus, among others. Injections of adrenocorticotropic hormone gel may be an alternative therapeutic option for those who do not react to or cannot handle existing medication therapies. Biologic medicines such as rituximab or tumour necrosis factor (TNF) inhibitors such as infliximab or etanercept may be used when other treatment options have failed in severe situations. However, relatively few trials have shown the efficacy of these medicines in treating polymyositis and dermatomyositis. Typically, physical therapy is prescribed to prevent muscular atrophy and preserve muscle strength and range of motion. Long-term bed rest should be avoided since it may lead to muscular atrophy, impaired muscle function, and joint contractures. A low-sodium diet may minimise oedema (swelling) and cardiovascular problems (heart and blood vessels). For their skin problem, many persons with dermatomyositis may need a topical ointment containing corticosteroids, tacrolimus, or pimecrolimus. Those who are sensitive to light should wear protective garments and sunscreen with a high SPF. Rarely, surgery may be necessary to remove calcium deposits that cause nerve discomfort and recurring infections. There is no standard course of therapy for the inclusion of body myositis based on scientific data. The condition is often resistant to corticosteroids and immunosuppressive medications. In a tiny number of patients, immunosuppressive drugs or intravenous immunoglobulin may have a modest but brief positive impact, according to some research. Physical therapy may aid in the preservation of mobility. The remaining treatment is symptomatic and supportive. 

The majority of instances with dermatomyositis respond well to treatment. In general, the condition is more severe and resistant to treatment in patients with cardiac issues. Approximately one-third of persons with juvenile-onset dermatomyositis recover, one-third have a relapsing-remitting disease history, and the other third have a chronic illness course. The outlook for polymyositis is variable. Some persons with a more severe condition do not react well to treatment, despite the fact that the majority of individuals respond rather well. These folks may be severely disabled. As polymyositis may cause trouble swallowing, malnutrition might occur. They are also more likely to have falls, which may result in hip and other bone fractures, incapacity, or death. Rarely, individuals with increasing and severe muscular weakening might suffer respiratory failure or pneumonia. Although necrotizing autoimmune myopathy is more difficult to treat than polymyositis and dermatomyositis, it often responds favourably to long-term immunosuppressive combination treatments. In general, IBM is resistant to all treatments, and current medications do nothing to halt its growth.

Polymyositis 

Polymyositis is an inflammatory myopathy, sometimes known as an inflammatory myopathy. It inflames your muscles and their associated tissues, such as their blood vessels. Oftentimes, it may cause muscle weakness and discomfort on both sides of the body. This continuous (chronic) illness is incurable, however, there are therapies that may alleviate symptoms. No one is aware of the precise aetiology of polymyositis. However, physicians are aware that it is an autoimmune disorder, meaning that the body may attack its own tissues. This is the root of the difficulties. It is more prevalent in individuals with other autoimmune disorders, such as lupus and rheumatoid arthritis. It is also more prevalent among HIV patients. The majority of polymyositis patients are diagnosed between the ages of 30 and 60. It is very uncommon in youngsters, and women are affected more often than males. 

Inflammation inside the muscles causes the symptoms of polymyositis. Both sides of the body are affected by muscular weakening equally. This ailment often affects the muscle groups closest to the trunk of the body, including the hips, shoulders, thighs, upper arms, upper back, and neck. If you have this condition, you may have difficulty raising your arms over your head, ascending flights of stairs, rising from a chair, and carrying objects. Occasionally, it may be difficult to swallow food, although this is uncommon. You may or may not experience discomfort in places with weak muscles. Over time, the muscles may atrophy, which means they may lose mass or volume. Usually, the illness progresses gradually, and you may not experience symptoms for months. Muscle weakness may be one of the first signs that you see. You may also believe you are unable to achieve all you once did. You may also have a fever, weight reduction, fatigue, and joint discomfort. Due to issues with blood flow, the fingers and toes become very chilly and discoloured in Raynaud's phenomenon. 

There are no straightforward diagnostic tests for polymyositis. Often, it takes time for physicians to confirm a diagnosis. Your doctor will investigate your and your family's medical histories to determine other problems. You may also be given the following tests: 

  • Blood testing may assist the physician to identify evidence of muscle injury. 
  • EMG: Determines whether or not the electrical impulse patterns in your muscles are normal. 
  • MRI (magnetic resonance imaging): This scans and creates pictures of vast muscle regions using a magnet. 
  • Your physician will take a tiny sample of your muscle for testing to determine if the muscle tissue is inflamed. An MRI may be necessary to assist your doctor to locate a suitable biopsy site. 

Polymyositis is a persistent disease. This implies that once obtained, it is retained. However, there are techniques to manage it. Typical therapies include: 

  • Steroids. These aid in reducing muscular inflammation, alleviating pain and even strengthening muscles. However, steroid use may have several negative effects, so your doctor will closely monitor you if they prescribe them. Most individuals begin treatment with prednisone, but if the condition is severe, the doctor may also prescribe methylprednisolone. 
  • Immune-suppressing pharmaceuticals. You may take them alongside steroids, or if steroids are ineffective, on their own. The doctor will likely prescribe azathioprine or methotrexate as the first treatment. 
  • Physical rehabilitation. This will increase your strength and mobility. 

Among the potential complications of polymyositis are: 

  • If your oesophageal muscles are compromised, you may have difficulty swallowing. It might cause weight loss and nutritional deficiencies. 
  • Aspiration pneumonia: If you have difficulty swallowing, you are more prone to inhale food or fluids (including saliva) into your lungs, which may lead to aspiration pneumonia. This may result in pneumonia. 
  • If your chest muscles are compromised, you may have shortness of breath or, in the worst case, respiratory failure. 

The prognosis for polymyositis is dependent on the severity of the condition. The majority of patients react to therapy and regain some muscular strength. There may be a residual weakness, and your symptoms may return. Even though the ailment is seldom life-threatening, if you do not react to therapy, you might become incapacitated. Polymyositis also increases the likelihood of developing an autoimmune disorder, cancer, or osteoporosis.

Myositis

Myositis refers to a set of uncommon conditions. The primary symptoms are muscular weakness, soreness, or discomfort. This often worsens gradually over time. You may also stumble or fall often and get quite fatigued when walking or standing. If anyone experiences any of these symptoms, you should see a physician. Myositis is often caused by an immune system disorder in which healthy tissue is wrongly attacked. Myositis UK, a nonprofit in the United Kingdom, contains a great deal of further information about the many kinds of myositis. There are three distinct forms of myositis, namely: 

  • Polymyositis, affects a variety of muscles, primarily the muscles of the shoulders, hips, and thighs. It is more prevalent in women between the ages of 30 and 60. 
  • Multiple muscles are affected by dermatomyositis, which generates a rash. It's more prevalent among women and may impact children (juvenile dermatomyositis).
  • IBM, causing weakness in the muscles of the thighs, forearms, and muscles just below the knee. It may also cause difficulty swallowing (dysphagia). IBM is more prevalent in males over 50 years of age. 

Polymyositis affects a variety of muscles, including those in the neck, shoulders, back, hips, and thighs. Among the symptoms of polymyositis include muscular weakness, hurting or painful muscles, and extreme fatigue. After a fall, difficulty sitting or standing, difficulty eating, difficulty holding your head up, unhappiness or depression. You may have trouble rising from a chair, climbing stairs, lifting things, and combing your hair. Even lifting up a cup of tea might be challenging if the muscular weakness becomes bad enough. The muscular weakness may fluctuate from week to week or month to month, but if left untreated, it tends to worsen slowly. 

Symptoms of dermatomyositis resemble those of polymyositis, with the addition of a unique rash. Before the onset of muscular complaints, a red, purple, or black rash often manifests. Typically, it affects the face (eyelids, nose, and cheeks) and hands (knuckles). Occasionally, it may also be observed on the back, upper chest, elbows, and knees. The rash may be uncomfortable or painful and may develop firm tissue lumps under the skin. 

IBM causes muscular weakening and degeneration in certain body regions. Most often affected are the wrists and fingers, the front of the thighs, and the front of the legs below the knee. Typically, these symptoms develop gradually, over a period of months or even years. Symptoms are not usually present on both sides of the body or perceived equally. The location, intensity, and onset of symptoms might vary from individual to individual. You may feel the following symptoms when the muscles in these regions progressively atrophy: 

  • Constant stumbling and falling 
  • Weakness of the quadriceps, hand, forearm, and ankle muscles. 
  • Knees giving way 
  • Loss of the ability to stand or hand dexterity 
  • Inability to raise the front of the foot (drop foot) 

A physician will inquire about the symptoms and do an exam to diagnose myositis. If they suspect that you have myositis, you will need to undergo certain tests to rule out other disorders with similar symptoms. Possible examinations include: 

  • Obtaining a tiny sample of muscle tissue or skin (biopsy) so that it may be analysed for oedema, injury, and other alterations 
  • Electromyography (EMG) is performed during MRI scans by inserting a tiny needle-shaped electrode under the skin and into the muscle to capture the electrical impulses from the nerve terminals in the muscle

Exercise is an essential component of the therapy for all forms of myositis. It may decrease inflammation, increase your vitality, and develop or restore muscular strength. As the sole therapies for this kind of myositis, exercise and physiotherapy are of utmost importance for individuals with IBM. IBM is not treatable with medications. Before beginning a new workout regimen for myositis, you should see a doctor and physiotherapist. They will help you create a personalised fitness regimen. You must exercise with extreme caution if you have severe myositis symptoms, such as significant muscular discomfort and weakness ("flare up"). The majority of experts do not encourage physical activity during this time. However, it is essential to keep modest mobility of your muscles and joints, particularly if myositis originated in infancy. This prevents your joints from stiffening and becoming stuck in place. 

Steroids are the most common treatment for polymyositis and dermatomyositis. They effectively decrease inflammation and alleviate muscular soreness. They may be administered as a pill, injection, or drip straight into a vein. You will often begin treatment with a high dosage, which will be gradually decreased over time. Long-term usage of steroids at high dosages might result in negative effects. Among them include weight increase, hypertension, diabetes, cataracts (cloudy patches in the lens of the eye as well as osteoporosis (weakened bones).  

If your muscle inflammation worsens, your physician may prescribe a disease-modifying anti-rheumatic medicine (DMARD). DMARDs, including azathioprine, methotrexate, cyclophosphamide, and mycophenolate, depress the immune system and aid in reducing inflammation. These medications take longer to take effect, but they may help you lower your steroid dosage over time. This may help reduce steroid side effects. 

Very infrequently, immunoglobulin treatment may be required to prevent your immune system from attacking your muscles. This entails receiving an injection of healthy blood-derived antibodies (immunoglobulins). Immunoglobulin treatment is often administered intravenously in a hospital setting. You may need many treatments. 

Biological medicines, such as rituximab, may also aid in the management of myositis symptoms. They are often used to treat illnesses including rheumatoid and psoriatic arthritis. They decrease inflammation and are often reserved for severe myositis. 

The majority of individuals with myositis react to a combination of steroid and immunosuppressive medication, as well as restricted exercise. Immunosuppressive drugs and very low dosages of corticosteroids are often required over several years. This may increase the likelihood of infection. If this becomes a problem, it can be readily treated with antibiotics in the majority of instances. Some individuals with myositis may not react well to therapy, and the illness has a substantial impact on their day-to-day living and quality of life. In most cases, however, continued exercise increases muscular strength. With severe myositis, breathing and swallowing difficulties may emerge. If you have difficulty swallowing or if it interferes with your ability to speak, speech and language therapy may be advised. In rare instances, myositis may be linked to cancer, and you may be given testing to detect the disease.

Myositis associated with an antisynthetase syndrome

Antisynthetase syndrome is an uncommon, persistent condition that may impact numerous physiological systems. The illness is immunological-mediated, meaning that inflammation is caused by aberrant immune activity and the existence of particular autoantibodies that target a specific protein in the body. Depending on the person, the disorder's symptoms and severity might vary substantially. Common symptoms include inflammation of the muscles (myositis), inflammation of several joints (polyarthritis), interstitial lung disease, thickening and cracking of the skin of the hands, and the Raynaud phenomenon, a disorder in which the fingers or toes become numb or prickly in reaction to cold. Additionally, affected people exhibit nonspecific symptoms such as tiredness, unexplained fevers, and unintentional weight loss. The precise root reason is not well known. Antisynthetase syndrome is occasionally accompanied by unusual inflammatory muscle illnesses such as dermatomyositis and polymyositis. Antisynthetase syndrome is an uncommon illness that occurs twice as often in girls as in men. The usual age of onset ranges from late teens to the elderly, with a mean of 50 years. The precise frequency or prevalence of the illness is unknown. Because uncommon conditions are often misdiagnosed or unrecognised, it is difficult to determine the real prevalence of antisynthetase syndrome in the general population. 

The indications and symptoms might vary significantly between individuals. Each individual is unique, and the disorder's impact on them might vary greatly. Rapid symptom development is possible. Typically, affected people will not exhibit all of the following symptoms. For instance, some afflicted people may have little muscular involvement but substantial lung illness symptoms. Generally, muscle disease, interstitial lung disease, and arthritis are regarded as the three most prominent signs of this condition (classic triad), however, they may not manifest simultaneously. Antisynthetase syndrome has the potential to harm the muscles. It is typical to have muscular inflammation (myositis), muscle discomfort (myalgia), and muscle rigidity. These conditions may result in muscular weakness. Inflammation of many joints may also develop (polyarthritis). Polyarthritis is characterised by joint pain and stiffness in afflicted joints. The adjacent bone is unaffected (non-erosive arthritis). Interstitial lung disease is characterised by increasing inflammation and scarring of the lungs, especially of the tissue and space around the alveoli. This region is known as the interstitium. This may cause shortness of breath, coughing, and swallowing difficulties (dysphagia). In certain cases, progressive lung deterioration may result in respiratory insufficiency (when the lungs are unable to provide enough quantities of oxygen to the body) and, ultimately, life-threatening respiratory failure. Nonspecific symptoms include inexplicable fevers, exhaustion, lack of appetite, unintentional weight loss, and skin rashes, such as heliotropic rash, a characteristic reddish-purple rash over the upper eyelid or across the cheekbones and bridge of the nose in a 'butterfly' pattern. Also possible are thickening, fissuring, and discolouration of the skin of the hands (called mechanic's hands). Some persons experience discomfort, numbness, or a prickling sensation in their fingers and toes when exposed to cold temperatures (Raynaud phenomenon). During an episode of Raynaud syndrome, the fingers and toes may become white or blue. 

Antisynthetase syndrome is diagnosed based on the identification of specific symptoms, a complete patient history, a comprehensive clinical assessment, and tests confirming the existence of autoantibodies against the enzyme aminoacyl-tRNA synthetase. 

  • Clinical Testing and Preparation: Autoantibodies against the enzyme aminoacyl-tRNA synthetase may be detected by blood testing. Antisynthetase syndrome does not emerge in every individual who has one of these autoantibodies. There are documented diagnostic criteria that have been suggested. However, these criteria are not widely recognised, and some clinicians believe that individuals could have antisynthetase syndrome even if they do not match the diagnostic standards outlined in these recommendations. According to the recommendations, persons with the illness must also exhibit two major criteria, one major criterion, or two minor criteria. Interstitial lung disease and muscular disease are the two most important requirements. Arthritis, Raynaud's phenomenon, and thickening and cracking of the skin of the hands (mechanic's hands) are minor requirements. Blood testing may also detect higher levels of the muscle enzymes creatine kinase and aldolase. The elevation of these muscle enzymes indicates muscular injury. This is not unique to the antisynthetase syndrome, but rather a symptom of several forms of muscle illness. 
  • CT scanning is a type of imaging technology that may be used to diagnose and assess lung illness. Throughout CT scanning, a computer and x-rays are used to produce a film containing cross-sectional pictures of certain tissue features. High-resolution CT scanning utilises certain procedures that increase or improve the picture resolution. Pulmonary function tests may be conducted to assess the adequacy or inadequacy of lung function. Specialised testing that captures electrical activity in skeletal muscle at rest and during muscular contraction (EMG) may be used to measure the health and performance of the muscles. 

Each individual's therapy for the antisynthetase syndrome is tailored to his or her own symptoms. The coordinated efforts of a team of experts may be required for treatment. General internists, specialists in the diagnosis and treatment of lung diseases (pulmonologists), specialists in the diagnosis and treatment of skeletal and muscle diseases (orthopedists), specialists in the diagnosis and treatment of immunological diseases (immunologists), and other healthcare professionals may be required to plan a child's treatment systematically and comprehensively. Also crucial is psychosocial assistance for the whole family. There are no established procedures or standards for the treatment of afflicted patients. Due to the rarity of the condition, there are no large-scale therapeutic studies have been conducted. In the medical literature, several therapies have been described as part of single case studies or small patient series. Antisynthetase syndrome patients would benefit greatly from treatment studies to evaluate the long-term safety and efficacy of various drugs and therapies. Corticosteroids or immunosuppressants may be used to treat affected patients (immunosuppressive drugs). The efficacy of these therapies and the length of time a patient needs to take these drugs will vary. To address skin problems, hydroxychloroquine has been used. Physical therapy is indicated to aid in the treatment of muscle disorders by enhancing muscular strength and preventing muscle atrophy. Drugs such as azathioprine, methotrexate, cyclophosphamide, cyclosporine, tacrolimus, mycophenolate mofetil, and rituximab have been used to treat afflicted patients. To assess the long-term safety and efficacy of these antisynthetase syndrome treatments, more study is required.

Immune-mediated necrotizing myopathy 

IMNM, also known as Necrotizing Autoimmune Myopathy (NAM), is a rare complement-mediated muscle illness that is classified as one of the Inflammatory Myopathies. IMNM may show similarly to polymyositis and causes muscle cell loss (necrosis) that leads to weakening of the symmetrical proximal muscles, such as the hips, thighs, upper arms, shoulders, and neck. Often significant muscle weakness may develop over a period of days, weeks, or months. This weakness may make it difficult to walk stairs, rise from a chair or the floor, turn in bed, raise, comb hair, brush teeth, or reach above the head for an object such as a shelf. There is no cure or FDA-approved therapy for IMNM. Certain drugs, particularly statins used to treat cholesterol, anti-HMGCR and anti-SRP autoantibodies, cancer, viral infections, and other connective tissue illnesses have been linked to IMNM. 

Myalgia (muscle pain) is a common symptom of immune-mediated necrotizing myopathy in many people. Others describe the pain as crushing and aching, while others describe it as intense and piercing. Finding adequate pain relief is often difficult. Discuss your pain with your physicians freely and honestly, and explain how it affects your life. IMNM signs and symptoms

  • Similar to polymyositis, symmetric, proximal muscle weakness (weakness is often severe) 
  • Weakness in other muscles, including breathing and swallowing muscles, and distal muscles (those located at the extremities of the body). 
  • Muscle pain (myalgia) 
  • Incapability or difficulty ascending steps, entering a vehicle, and standing up from a sitting posture. 
  • Washing, combing, or brushing one's hair, or extending arms to raise an object such as placing a dish in a cupboard, may be challenging. 
  • Dysphagia (trouble swallowing) 
  • Excruciating and incapacitating fatigue 
  • Weight reduction 

Due to the rarity of IMNM, diagnosis and treatment are often administered by a specialised centre with expertise in diagnosing and treating inflammatory myopathies, which may consist of rheumatologists, neurologists, and neuromuscular experts. This may be in collaboration with the patient's primary care doctor (PCP). Any experts, such as a cardiologist, pulmonologist, oncologist, endocrinologist, and pain management, may need to be consulted, depending on the patient's symptoms, other concurrent conditions, and organ involvement. 

Physical activity is essential for myositis sufferers. Therefore, you may also visit a physical therapist, an occupational therapist, and a speech-language pathologist if you have difficulty swallowing (dysphagia). 

Clinical and Physical Exam: A detailed medical and family history is crucial for diagnosing a rare and complicated condition like IMNM. We recommend drafting a comprehensive medical and family history that can be shared with your medical team and utilised for all future consultations. Physical examination and detailed medication history are also crucial. 

Blood testing: If your physician suspects IMNM, he or she will likely request a battery of blood tests to assess autoimmune and inflammatory markers and to detect myositis-specific and myositis-associated antibodies, cancer markers, and other antibodies. These assessments may include: 

  • Creatine Kinase (CK or CPK) is an enzyme that breaks down creatine (muscle enzymes) 
  • Aldolase LD and ALT and AST (Lactate dehydrogenase) 
  • Sedation Rate (also called ESR or Erythrocyte sedimentation rate) 
  • ANA (Antinuclear Antibodies panel) 
  • Testing for HMGCR and SRP antibodies (found in roughly two-thirds of patients) 
  • Study of EMG and Nerve Conduction (NCS) 

EMG is a test that evaluates the health of muscles and nerves that govern muscles. Similar to other inflammatory myopathies, the EMG may reveal an irritable myopathy pattern in patients with IMNM. EMG testing may assist differentiate between weakness caused by muscle illness and nerve abnormalities. During the same visit, a nerve conduction study is performed to determine how quickly electrical impulses travel across a nerve. MRI is increasingly employed and may detect changes that indicate muscular inflammation. Additionally, physicians may utilise MRI to choose the optimal muscle for biopsy. 

The muscle biopsy is essential for diagnosing IMNM, particularly when the antibodies (HMGCR and SRP) are negative. Using either a needle biopsy or an open surgical biopsy, the physician will take a tiny sample of muscle tissue for laboratory analysis. Typically, an open muscle biopsy is performed as an outpatient operation, but you and your physicians will establish the specifics. Your physician will choose the weakest muscle for biopsy, avoiding the region of any recent EMG. An MRI may aid in finding the optimal biopsy muscle. 

Other tests: The tests listed above are not a complete list of those that your doctor may order. Additional tests will depend on your symptoms and any associated conditions. 

Since cancer may be related to certain occurrences of IMNM, your doctor may do more cancer tests beyond those recommended for your age and race. 

It was originally believed that stopping the offending medicine, such as statins, would eradicate IMNM symptoms within weeks or months. In recent years, however, it has become apparent that some patients who cease the medicine do not recover or improve because an autoimmune mechanism is at play in these people. No FDA-approved treatments are available for IMNM or any of the inflammatory myopathies. Patients utilise unapproved drugs with minimal scientific support. Immunosuppressive drugs are the most frequent conventional medications used to treat a variety of different autoimmune illnesses. After many weeks of high-dose corticosteroids, patients may see an improvement. The physician will likely do a follow-up physical examination and CK/CPK blood test to see whether the patient's muscular strength has improved and the levels of CK/CPK have reduced. The objectives of therapy for IMNM are to remove or minimise inflammation, restore muscular function and strength, reduce morbidity, and enhance the quality of life of the patient. 

In addition to steroids, which are a typical therapy for inflammatory myopathies but are not indicated for long-term usage, there are no FDA-approved treatments for IMNM. Often, a combination of drugs is required for effective therapy. If you are currently taking a statin, your physician will likely terminate its use. The first therapy is often corticosteroids, such as prednisone or prednisolone, dosed at 1 mg per kg according to the patient's weight. Corticosteroids treat inflammation and inhibit an overactive immune system concurrently. Steroids administered intravenously (IV), such as methylprednisolone, may also be utilised. Steroids have several adverse effects, including weight increase and redistribution of body fat to the face, neck, and abdomen; raised blood sugars, mood swings, skin thinning, cataracts, and osteoporosis; and weight gain and redistribution of body fat to the face, neck, and abdomen. Additional medications to suppress the immune system may be given to steroids, sometimes at the start of therapy and sometimes after it has been shown that steroids are successful. The introduction of steroid-sparing drugs should be explored when appropriate, given that steroids are known to induce a variety of undesirable side effects, particularly when used at large dosages and for extended periods. In addition to reducing or eliminating the requirement for steroids, steroid-sparing medications, such as immunosuppressive drugs, offer the additional advantage of dampening a hyperactive immune system. However, there are hazards associated with these drugs. Mycophenolate mofetil (Cellcept), azathioprine (Imuran), and methotrexate are immunosuppressive medications used in conjunction with NAM. 

Immunoglobulin Therapy (IVIg, SubQ Ig): Immunoglobulin is derived from plasma-extracted antibodies from tens of thousands of blood donors. IVIg is administered intravenously (IV). SubQ Ig is also available and may be authorised for certain patients; it is injected under the skin more quickly and removes the need for constant home nursing. Observational studies indicate that statin-exposed anti-HMGCR-positive patients often see substantial improvement with intravenous immunoglobulin, but statin-naive anti-HMGCR patients may be resistant to any immunosuppressive medication. 

Rituximab (Rituxan) is a member of the monoclonal antibody medication class. It's administered intravenously. Observational studies indicate that anti-SRP patients react well to rituximab therapy. 

The prognosis of IMNM relies on several variables, such as the response to existing therapies, none of which are FDA-approved for IMNM, the severity of illness and its symptoms, the existence of pulmonary or cardiac involvement, and the presence of related autoantibodies or cancer. Some people with IMNM react very well to therapy, however, others may not. Finding the appropriate medicine or treatment combination might take a very long time. Some drugs need months to become effective. Long-term steroid usage may be a significant contributor to morbidity.

Summary

There are several forms of autoimmune muscle diseases, and their symptoms often overlap. This may make an accurate diagnosis challenging. It is considered that autoimmune disorders are the chief reason for disability and mortality. Therefore, anybody who suspects that might well have one should see a physician.

References

  1. Inflammatory Muscle Diseases. New England Journal of Medicine. 2015;373(4):393-394.
  2. Smoyer-Tomic K, Amato A, Fernandes A. Incidence and prevalence of idiopathic inflammatory myopathies among commercially insured, Medicare supplemental insured, and Medicaid enrolled populations: an administrative claims analysis. BMC Musculoskeletal Disorders. 2012;13(1).
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Sara Maria Majernikova

Bachelor of Science - BSc, Biomedical Sciences: Drug Mechanisms, UCL (University College London)
Experienced as a Research Intern at Department of Health Psychology and Methodology Research, Faculty of Medicine, Laboratory Intern at Department of Medical Biology, Faculty Medicine Biomedical Sciences Research Intern and Pharmacology Research Intern.

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