What is Autoimmune Myopathies?

Idiopathic inflammatory myositis (IIM), a condition where the muscles become inflamed, can be broken down into four subtypes. These include polymyositis and dermatomyositis (PM/DM), immune-mediated necrotizing myopathy, and inclusion body myositis. They are categorized based on symptoms and the changes we can see in the muscle tissues under a microscope.

The fact that antibodies (proteins our body usually uses to fight off invaders) and inflammation are found in the muscles of those with IIM implies that it might occur due to the body’s immune system attacking its own cells. However, the exact triggers or targets of this attack within the body’s system have not been found yet.

Polymyositis and dermatomyositis (DM), are particularly interesting because they show a lot of similarities and can be discussed together. They both commonly lead to muscle weakness that is symmetric and closest to the body.

When doctors diagnose these conditions, they often look for unique features. These can include muscle weakness, higher levels of enzymes (proteins that help chemical reactions happen) in the blood that usually indicate muscle damage, abnormal electric activity in muscles, certain changes in muscle tissues, and a specific rash that is usually associated with dermatomyositis.

What Causes Autoimmune Myopathies?

Inflammatory myopathies are diseases caused by an overactive immune system. They are often triggered by outside influences in people who have a certain genetic makeup which makes them more susceptible to these diseases.

The outside influences, known as environmental factors, include drugs, infections, UV light, a lack of vitamin D, and smoking. Some medicines like penicillamine, interferon-alpha, and even medication that stops tumor necrosis factor have been linked to cases of myositis, which is similar to polymyositis and dermatomyositis. Also, having antibodies for the Coxsackie virus is more common in patients with juvenile diabetes mellitus, suggesting that an infection could trigger these diseases. However, we still need more definitive evidence to prove if ongoing viral infection can cause chronic muscle inflammation.

The possibility of inheriting these diseases from family members exists, especially among identical twins or close blood relatives with the conditions. This hints at a genetic factor, but it’s complicated. The genes that could contribute to these diseases differ around the world. Among them, HLA DRB1 *0301 and the linked DQA1 *0501 are seen as the strongest risk factors.

Risk Factors and Frequency for Autoimmune Myopathies

  • The number of people who have polymyositis and dermatomyositis (PM/DM) is estimated to be 5 to 22 per 100,000 persons.
  • The number of new cases each year is approximately 1.2 to 19 per million persons at risk.
  • The rate of myositis is rising due to better detection methods.
  • Dermatomyositis usually appears in two age groups: 5 to 15 years and 45 to 60 years.
  • Polymyositis is rare in children and usually affects people aged 50 to 60.
  • Women are 2 to 3 times more likely to have these conditions than men.
  • In the United States, the conditions are 3 to 4 times more common in the Black population compared to the White population.
  • In Europe, these conditions are more common in the south than in the north, possibly due to environmental or genetic factors.

Signs and Symptoms of Autoimmune Myopathies

Idiopathic inflammatory myopathies (IIM) primarily cause symmetric muscle weakness. This often makes it hard to stand from a seated position, climb stairs, lift heavy things, or move the arm above the head. Dermatomyositis, a type of IIM, often includes a special skin rash in addition to muscle weakness. The specific rashes include the Gottron papule and heliotrope rash.

  • Heliotrope rash: This is a purple-colored rash on the eyelids, sometimes paired with swelling around the eyes.
  • Gottron papules: This is a reddish rash, which has variable small raised spots, appearing on the backs of the hands, particularly across the finger joints.
  • Gottron sign: Similar to Gottron papules, but these reddish spots or patches can appear on places other than the hands, like on the elbows, knees, and ankles.
  • Shawl sign: Shows a reddish rash on the chest (in a V-sign) and upper back.
  • Mechanic’s hands: Features widened blood vessels at the base of the fingernails, irregular and thickened cuticles, and cracked fingertips.
  • Holster sign: Displays discolored skin on the sides of the thigh (areas usually protected from sunlight).

Notably, these rashes, except the holster sign, become worse when exposed to sunlight. Other symptoms include changes in the nail bed and around the nails, reddening over the forehead, chin, and knees; sensitivity to sunlight; rashes on the chest and upper back; localized fat inflammation; and skin hardening due to calcium deposits.

In some cases of dermatomyositis, the disease presents uniquely and is identified by specific proteins known as autoantibodies. Some patients with dermatomyositis might experience little to no muscle symptoms. This is often referred to as hypomyopathic or amyopathic dermatomyositis.

Beyond muscle weakness and skin changes, IIM can also cause joint inflammation, cold-induced color changes in the fingers or toes (Raynaud phenomenon), difficulty swallowing (dysphagia), and a lung condition known as interstitial lung disease.

Testing for Autoimmune Myopathies

If a person’s medical history suggests they have muscle weakness, doctors often first check their muscle enzymes. These include creatine phosphokinase (CPK), aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase (LDH), and aldolase. A high CPK level often points to severe muscle inflammation though, sometimes, it can be normal. Measuring these enzymes over time can help track the activity of myositis, a type of muscle inflammation, and can be used alongside strength tests. Inflammatory markers like ESR and CRP can also be increased. Autoantibodies, muscle imaging, electrophysiologic examination, and muscle biopsy can confirm a myositis diagnosis. Over 80% of patients with myositis have autoantibodies.

There are two types of these autoantibodies: myositis-specific antibodies and myositis-associated antibodies. Myositis-specific antibodies are found in particular types of myositis. They include antisynthetases, which are a group of antibodies that target certain enzymes, as well as dermatitis-associated antibodies. Examples of these are Anti Jo-1, Anti-Mi-2, Anti-MDA5, Anti-TIF, Anti-SAE, and Anti-NXP. Myositis-associated antibodies are not specific to a particular disease and often occur in patients with multiple conditions. These include anti-PM SCL, anti-Ro, anti-La, anti-Ku, and anti-U1 RNP.

If these muscle enzymes are found to be abnormal, doctors can use an EMG or MRI to examine muscle inflammation. This can help them identify which area to biopsy, or remove a small piece of tissue for testing.

In an EMG, doctors look for patterns that suggest inflammation, including low amplitude, short duration, and polyphasic potential; increased membrane irritability; spontaneous fibrillation; and early recruitment. It’s important to only perform this test on one side, so that the other side can be used for the biopsy without having any electrical burn artefacts. An MRI can help to spot inflammation, scarring, and muscle atrophy.

A muscle biopsy can help to distinguish between two types of myositis: polymyositis and dermatomyositis. In those with dermatomyositis, a biopsy of the skin will show mild weakening of the top layer of skin, vascular changes at the base, and inflammation around the blood vessels in the dermis, or second layer of the skin.

All patients with either type of myositis should have a chest X-ray to check for lung involvement, such as interstitial lung disease. Depending on the patient’s symptoms and the results of the X-ray, they may also need pulmonary function tests and a CT scan of the chest. There’s an increased risk of cancer in patients with inflammatory myositis, particularly dermatomyositis. Therefore, these patients should also have routine cancer screenings, such as colonoscopy, low dose CT chest, Pap smear, and mammography, alongside routine blood tests, chemistries, and urinalysis. Those with dermatomyositis who test positive for anti-NXP2 or anti-TIF one antibody are at an even higher risk of cancer. They should consider a PET/CT scan, as they are at an increased risk of cancer within three years of their diagnosis.

Treatment Options for Autoimmune Myopathies

Corticosteroids like prednisone are primarily used to manage health conditions such as polymyositis and dermatomyositis. Physicians usually recommend a treatment plan that begins with prednisone 1 to 2 mg/kg/day. For patients with severe weakness or those with involvement of other body parts, intravenous methylprednisolone 1mg/day for three days can be helpful. Patients should be carefully monitored, and the dosage of steroids can be slowly reduced depending on how they respond to the treatment. No specific rules exist for the initial dosage or reduction of steroids, so it’s important to manage this treatment under an experienced doctor. The treatment process should be customised to the patient’s needs. To manage the potential side effects of steroids, such as bone loss, muscle weakness, high blood pressure, increased blood sugar, and weight gain, patients and their families should learn about the disease and how it is treated.

For patients who experience side effects from the steroids or those who find it hard to reduce the steroid dose, or if the steroids are not as effective as expected, additional treatments might be considered. These can include methotrexate and azathioprine, two drugs that can help manage the disease without needing as much of the steroids. However, these drugs should be utilised consciously if the patient has lung complications as they can potentially risks. Calcineurin inhibitors and mycophenolate mofetil can be beneficial for skin conditions and lung disease. Cyclophosphamide, another drug, is used for severe and fast-progressing lung diseases, but it carries the risk of infertility. Also, intravenous immunoglobulins can be advantageous for dermatomyositis.

Rituximab, a biologic drug, is helpful for myositis and related lung diseases. As it is generally safer and easier for patients to tolerate than other drugs, it is often the preferred choice over cyclophosphamide. Moreover, other biologic drugs, such as tocilizumab, anakinra, alemtuzumab, tofacitinib, and ruxolitinib, have also shown some effectiveness for autoimmune myositis, but these are typically used when other treatments haven’t worked.

A personalized exercise program designed and supervised by a physical therapist can help build strength and reduce the impact of the illness. Sun avoidance, use of sunscreens, and precautions in patients with throat muscle weakness are among the supportive treatments for these conditions.

When diagnosing diseases like polymyositis and dermatomyositis (PM/DM), doctors might check for the following medical conditions that could have similar symptoms:

  • Other muscle inflammation disorders such as inclusion body myositis and immune-mediated necrotizing myopathy
  • Muscle weakness due to certain medications (known as drug-induced myopathy)
  • Nerve damage diseases like motor neuron disease
  • Autoimmune diseases that affect nerve and muscle like myasthenia gravis and Lambert-Eaton syndrome
  • Hypothyroidism which could slow down the body’s function
  • Diseases causing progressive weakness in muscles such as muscular dystrophy and myotonic dystrophy
  • Amyotrophic lateral sclerosis, a type of nerve disease that affects muscle movements
  • Presence of amyloid proteins which could affect the muscle function (known as amyloid myopathy)
  • Organ-specific inflammation disease like sarcoid myopathy
  • Diabetic amyotrophy, a nerve disorder often occurring in diabetic patients

A doctor may consider all these possibilities and perform the necessary tests to determine the most accurate diagnosis.

Frequently asked questions

Autoimmune myopathies are a group of conditions where the body's immune system mistakenly attacks its own muscle cells, leading to muscle inflammation and weakness.

The number of people who have polymyositis and dermatomyositis (PM/DM) is estimated to be 5 to 22 per 100,000 persons.

The signs and symptoms of Autoimmune Myopathies include: - Symmetric muscle weakness, making it difficult to stand from a seated position, climb stairs, lift heavy things, or move the arm above the head. - Dermatomyositis, a type of Autoimmune Myopathy, often includes a special skin rash in addition to muscle weakness. - Specific rashes associated with dermatomyositis include the Heliotrope rash, which is a purple-colored rash on the eyelids, sometimes paired with swelling around the eyes, and the Gottron papules, which is a reddish rash with variable small raised spots appearing on the backs of the hands, particularly across the finger joints. - Other skin manifestations of dermatomyositis include the Gottron sign, which is similar to Gottron papules but can appear on places other than the hands, like on the elbows, knees, and ankles, and the Shawl sign, which shows a reddish rash on the chest (in a V-sign) and upper back. - Mechanic's hands is another skin manifestation, characterized by widened blood vessels at the base of the fingernails, irregular and thickened cuticles, and cracked fingertips. - The Holster sign displays discolored skin on the sides of the thigh, areas usually protected from sunlight. - These rashes, except the holster sign, become worse when exposed to sunlight. - Other symptoms of Autoimmune Myopathies include changes in the nail bed and around the nails, reddening over the forehead, chin, and knees, sensitivity to sunlight, rashes on the chest and upper back, localized fat inflammation, and skin hardening due to calcium deposits. - In some cases of dermatomyositis, the disease presents uniquely and is identified by specific proteins known as autoantibodies. - Some patients with dermatomyositis might experience little to no muscle symptoms, known as hypomyopathic or amyopathic dermatomyositis. - Beyond muscle weakness and skin changes, Autoimmune Myopathies can also cause joint inflammation, cold-induced color changes in the fingers or toes (Raynaud phenomenon), difficulty swallowing (dysphagia), and a lung condition known as interstitial lung disease.

Autoimmune myopathies are caused by an overactive immune system and can be triggered by outside influences such as drugs, infections, UV light, a lack of vitamin D, and smoking. There is also a possibility of inheriting these diseases from family members, especially among identical twins or close blood relatives.

The doctor needs to rule out the following conditions when diagnosing Autoimmune Myopathies: 1. Other muscle inflammation disorders such as inclusion body myositis and immune-mediated necrotizing myopathy. 2. Muscle weakness due to certain medications (known as drug-induced myopathy). 3. Nerve damage diseases like motor neuron disease. 4. Autoimmune diseases that affect nerve and muscle like myasthenia gravis and Lambert-Eaton syndrome. 5. Hypothyroidism which could slow down the body's function. 6. Diseases causing progressive weakness in muscles such as muscular dystrophy and myotonic dystrophy. 7. Amyotrophic lateral sclerosis, a type of nerve disease that affects muscle movements. 8. Presence of amyloid proteins which could affect the muscle function (known as amyloid myopathy). 9. Organ-specific inflammation disease like sarcoid myopathy. 10. Diabetic amyotrophy, a nerve disorder often occurring in diabetic patients.

The types of tests needed for autoimmune myopathies include: - Muscle enzyme tests: Creatine phosphokinase (CPK), aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase (LDH), and aldolase. - Inflammatory markers: ESR and CRP. - Autoantibody tests: Myositis-specific antibodies and myositis-associated antibodies. - Muscle imaging: EMG (electromyography) and MRI (magnetic resonance imaging). - Muscle biopsy: To confirm the diagnosis and distinguish between different types of myositis. - Chest X-ray: To check for lung involvement. - Pulmonary function tests and CT scan of the chest: Depending on the symptoms and X-ray results. - Cancer screenings: Colonoscopy, low dose CT chest, Pap smear, and mammography. - Routine blood tests, chemistries, and urinalysis. - PET/CT scan: For patients at an increased risk of cancer. - Corticosteroids: Primarily used for management, such as prednisone. - Additional treatments: Methotrexate, azathioprine, calcineurin inhibitors, mycophenolate mofetil, cyclophosphamide, intravenous immunoglobulins, rituximab, and other biologic drugs. - Personalized exercise program supervised by a physical therapist. - Supportive treatments: Sun avoidance, use of sunscreens, and precautions for throat muscle weakness.

Autoimmune myopathies, such as polymyositis and dermatomyositis, are primarily treated with corticosteroids like prednisone. The treatment plan usually starts with a dosage of prednisone 1 to 2 mg/kg/day. For patients with severe weakness or involvement of other body parts, intravenous methylprednisolone 1mg/day for three days can be helpful. The dosage of steroids can be slowly reduced based on the patient's response to the treatment. Additional treatments, such as methotrexate, azathioprine, calcineurin inhibitors, mycophenolate mofetil, cyclophosphamide, intravenous immunoglobulins, rituximab, and other biologic drugs, may be considered for patients who experience side effects from steroids or if steroids are not as effective. A personalized exercise program supervised by a physical therapist and supportive treatments like sun avoidance and use of sunscreens may also be part of the treatment.

The side effects when treating Autoimmune Myopathies with corticosteroids like prednisone can include bone loss, muscle weakness, high blood pressure, increased blood sugar, and weight gain.

The text does not provide information about the prognosis for autoimmune myopathies.

Rheumatologist.

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