We don't give medical advice, but the following sections provide basic information on the different types of Myositis:
Myositis (pronounced my-oh-sigh-tis) is the general term for a group of muscle diseases in which the body’s immune system attacks the healthy muscle cells. Neurologists call the process an inflammatory myopathy and over a period will lead to muscle weakness and atrophy.
The Myositis Association provides the following information on the types of Myositis:
Polymyositis (PM) is found mostly in people over the age of 20 and affects more women than men. Muscle weakness usually happens over days, weeks, or months. The weakness begins with muscles closest to and within the trunk of the body, such as the muscles of the neck, hips, back, and shoulders. Some patients also feel weakness in muscles farther from the trunk, such as hands and fingers. Some PM patients may also experience muscle pain, breathing problems, and trouble swallowing.
Signs and symptoms:
Dermatomyositis (DM) affects people of any age or sex, but is found in more women than men. Dermatomyositis is becoming more prevalent in African-American women for reasons that are poorly understood.
DM is the easiest type of myositis to diagnose because of the skin rash which is often seen before any muscle weakness is felt. The DM rash looks patchy, dusky, and reddish or purple. It is found on the eyelids, cheeks, nose, back, upper chest, elbows, knees and knuckles. Some people also have hardened bumps under the skin, called calcinosis. The skin rash and weak muscles are caused by inflammation, or swelling, in the blood vessels under the skin and in the muscles, also called vasculitis. Patients who have the skin rash but feel no muscle weakness have amyopathic DM, or DM sine myositis.
The weakness begins with muscles that are closest to and within the trunk of the body. Neck, hip, back and shoulder muscles are examples. Some DM patients have muscle pain.
Signs and symptoms:
Sporadic inclusion body myositis (sIBM) is the most common acquired myopathy in patients over the age of 50. It is unlike all other forms of myositis in terms of symptoms, treatment, and who it affects. More men have inclusion body myositis than women, and the disease is rarely seen in people younger than 50 years of age. Symptoms of inclusion body myositis progress more slowly than the other types of myositis with weakness increasing gradually, sometimes over years. For this reason it is not uncommon for patients to realize that they had been experiencing symptoms for many years before they were diagnosed.
There is currently some debate among myositis experts about whether or not inclusion body myositis is actually an inflammatory disease. On one hand, inflammatory cells are present in muscle tissue from patients with inclusion body myositis, especially earlier in the disease process, but their role in causing muscle weakness is unclear. In addition, autoantibodies have been found in patients with sIBM, suggesting an inflammatory process. On the other hand, the weakness appears to be the result of a degenerative process within the muscles, and the disease does not respond to treatment with anti-inflammatory medications. Most experts agree, however, that an eventual treatment and cure will likely require attention to both inflammation and muscle degeneration.
Sporadic inclusion body myositis should not be mistaken for hereditary inclusion body myopathy (hIBM). Although muscle biopsy findings in the hereditary myopathies share some of the same features seen in sporadic IBM—rimmed vacuoles and inclusions in muscle cells—these two conditions are otherwise quite different. The hereditary form of the disease is caused by a gene defect, not inflammation. The average age of onset in hIBM is between the teenage years and mid-twenties, not in older age. Muscle weakness in hIBM is usually distal (in the extremities) and may include eye muscles and other areas of weakness. CK levels range from normal to slightly elevated, and EMG results are normal.
Some of the first signs of inclusion body myositis are falling, difficulty getting up from a chair, and weakened grip. Muscles most often affected are those at the front of the thighs, those that elevate the feet, and those in the hips, fingers, wrists, upper arms, shoulders, neck, back, and, less often, in the face. Many IBM patients notice shrinking (atrophy) in the arms and thighs as the muscles become weaker. Trouble swallowing (dysphagia) is a common problem for patients with sIBM.
Signs and symptoms
Juvenile Myositis (JM) is found in children under the age of 18 and affects 3,000 to 5,000 children in the United States. The most frequent form of JM is juvenile dermatomyositis (JDM), in which children experience marked muscle weakness and skin rash. The other form of myositis that can occur in children—juvenile polymyositis—is extremely rare.
The first sign of JDM is usually a skin rash. The rash may be red and patchy, like dry skin; a red or purplish color on the eyelids or cheeks that may look more like allergies; or both. Children with juvenile polymyositis do not experience skin symptoms.
JDM patients can have weak muscles at the same time they see the skin rash, or the weakening muscles may occur after the rash over days, weeks, or months. The weaker muscles are usually those closer to the body, in the neck, shoulders, back, and torso. The child may have trouble climbing or standing from a seated position. The skin rash and weak muscles are caused by inflammation or swelling in the blood vessels under the skin and in the muscles.
Other signs may include falling, weaker voice (dysphonia), or problems swallowing (dysphagia). About half of the children with JDM have pain in their muscles.
Some children may develop calcinosis, hardened lumps or sheets of calcium under the skin. Contractures can also occur in which the muscle becomes shortened, causing the joint to stay bent. Exercising the muscles and joint range of motion can prevent contractures.
Signs and symptoms:
Necrotizing myopathy (also called necrotizing autoimmune myopathy [NAM] or immune-mediated necrotizing myopathy [IMNM]) is a newly defined form of idiopathic inflammatory myopathy. In the past, all patients who presented with muscle weakness, elevated creatine kinase levels, and other symptoms of myopathy, but who didn’t have skin involvement, were classified as having polymyositis. Now, it is recognized that some of these patients have unique findings on their muscle biopsies that distinguish them from those with other forms of myositis.
Patients with necrotizing myopathy have muscle biopsies that show much less inflammation in muscle tissue than polymyositis patients, but they have increased evidence of muscle cell death (necrosis).
Researchers are also beginning to distinguish different categories of necrotizing myopathy that have different risk factors and different treatments. These distinctions are based on the presence of different autoantibodies in the patient’s blood and probably mean that these are different diseases. These different forms include:
Signs and symptoms
Like other forms of myositis, patients with necrotizing myopathy may experience: