Inflammatory Myopathies or Immune System Diseases

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When someone is weak, neurologists try to figure out whether the source of that weakness is the muscle itself, the junction between nerve and junction, peripheral nerve, spinal cord or the brain.   If someone’s signs and symptoms suggest disease in the muscle itself, this may be confirmed by various tests, such as electromyograms, biopsies, or even genetic testing.

Many muscle diseases are strongly associated with a particular genetic mutation, and may come on in childhood.

  Other diseases, seem to be acquired more spontaneously in adulthood.  While these disorders may sometimes be associated with a genetic mutation, there is no direct causal relationship between the mutation and the disease. 

Inclusion body myositis

Inclusion body myositis breaks many of the “rules” of muscle disease.   Whereas most muscle diseases equally weaken both sides of the body, inclusion body myositis often weakens one area more than another.  Also, most muscle diseases impact muscles close to the center of the body, like the shoulders, more than those further away, such as the hands.  But frequently inclusion body myositis weakens muscles far from the body first. 

A classical case  of inclusion body myositis might begin in the wrist and fingers, but also involve the muscles of the thigh and calf.  The muscles of the face and shoulders tend to be spared.  Muscles of the mouth and throat are often involved, though, which can result in difficulty swallowing.

 

The disorder is likely an autoimmune reaction, as lymphocytes (cells involved in an immune response) are often found in affected muscles.  Two genetic variations associated with multiple sclerosis, an autoimmune disease, have also been found to be more common in people with inclusion body myositis.

 

The disorder is diagnosed by a muscle biopsy, which shows a characteristic protein deposit inside the muscle.  These “inclusion bodies” give the disease its name.

At this time there is no effective treatment.  Progressive weakness is expected. 

Dermatomyositis

Dermatomyositis is an inflammatory disease that can come on either in childhood or adulthood. 

Children with this myopathy often have signs of viral exposure first.  Ninety percent of cases are associated with the genetic variant HLA-DQ, which is also associated with increased risks of multiple sclerosis. Adults who develop dermatomyositis often, but not always, have antibodies against the Mi-2 protein. 

The symptoms of the disease include pain and weakness in muscles close to the body’s center, such as shoulders and thighs.  Difficulty swallowing is common. A rash also develops over sun-exposed areas of skin, especially the face, eyelids, and neck.  The skin on the elbows and knees can thicken.

When the blood is tested in a laboratory, a protein called creatine kinase (CK) is typically very high—up to 30 times the normal limit.

  A muscle biopsy will show inflammation around blood vessels in the muscle, with areas of cell death and regrowth.

Dermatomyositis is treated with immunotherapies such as solu-medrol, and prednisone.  Other immunosuppressants like azathioprine or methotrexate may also be used.  Such treatments may take two to three months before improvement is noted. 

Polymyositis

Polymyositis is another inflammatory muscle disease that usually progresses over weeks or months.  Symptoms include weakness and pain in the thighs and shoulders.  Facial muscles are normal except for in advanced cases, though about 30% of cases may have involvement of the esophagus, leading to difficulty swallowing.

Sometimes polymyositis may be part of a broader autoimmune disease.  The average age of onset in such cases is relatively young at about 35 years.  Women tend to be more commonly affected than men. Polymyositis is sometimes associated with problems with the heart or lungs. 

To diagnose polymyositis, physicians may check creatine kinase levels in the blood, which can be very high in polymyositis.  Ultimately, a muscle biopsy may be helpful.  Under the microscope, one can see the destruction of muscle fibers by inflammatory cells.

Sarcoid myopathy

Sarcoidosis is an autoimmune disease that impacts several different organs.  The disease is about 10 to 20 times more common in African-Americans than Caucasians.  It usually presents with characteristic skin findings as well as arthritis.  That said, the lungs, brain and more can also be impacted.  A large percentage of patients with sarcoidosis have evidence of muscle disease when a biopsy is examined under the microscope, even though many of these patients never had symptoms.   Sometimes, though, people develop painful aches in their muscles, wth muscle weakness and wasting as well. 

A chest X-ray may show additional signs of sarcoidosis in lymph nodes.  A muscle biopsy will show classic collections of inflammatory cells called a granuloma.  The prognosis is generally good—remissions are more common than not.  Corticosteroids may provide relief.

Vasculitic Myopathy

Inflammatory diseases can impact blood vessels, and that impacts muscles as well as other parts of the body.  Examples include polyarteritis nodosa, Churg-Strauss syndrome, and Wegener’s granulomatosis.

In summary, there are many different forms of myositis, all causing muscle weakness, and pain.  While it may not always be possible to cure the disease, some relief may result with the use of immune modifying drugs. 

Source: 

Nima Mowzoon, Disorders of Muscle, Neurology Board Review: An Illustrated Study Guide, 2007 

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