What is it?

Arthritis is a complex family of musculoskeletal disorders consisting of more than 100 different diseases or conditions that destroy joints, bones, muscles, cartilage and other connective tissues, hampering or halting physical movement. Myositis is defined as the inflammation of muscles (“myo” means muscle and “itis” means inflammation). The inflammatory myopathies are a group of disorders characterized by inflammation and weakness mainly of the muscles closest to the trunk of the body (proximal muscles). These disorders include polymyositis, dermatomyositis and inclusion body myositis. Myositis may be associated with inflammation in other organs, including the joints, heart, lungs, intestines and skin. In dermatomyositis, a rash develops in addition to the muscle inflammation.

What are the effects?

Each of the disorders associated with Myositis have different effects.

Characteristics of Polymyositis can include:

  • Flares: Flares usually are recognized by increasing symptoms of muscle weakness, fatigue, skin changes or arthritis.
  • Proximal muscle weakness: Symmetric weakness of the large muscles closest to the trunk of the body is the main symptom of polymyositis. Initially, hips, thighs and shoulders are commonly affected. Shoulder and pelvic girdle muscles are most severely affected. The weakness may make it difficult to lift heavy objects, climb stairs, or lift your arm to comb hair or put on a coat.
  • Lung problems: Polymyositis can cause weakness of the muscles required for breathing. It may also cause fibrosis (build up of excessive scars tissue) of the lungs, which results in coughing and shortness of breath.
  • Systemic symptoms: You may experience fever, weight loss, general malaise and Raynaud’s phenomenon (an extreme sensitivity and discoloration to cold, especially in your fingers).
  • Joint pain: Pain in the joints commonly occurs during periods when the disease is active, but the joints are not usually warm or swollen.

Dermatomyositis is an inflammatory muscle disease, like polymyositis; however, it has a somewhat severe onset and affects both children and adults. Clinical features of dermatomyositis include all those of polymyositis, plus a variety of skin manifestations.

Juvenile dermatomyositis differs from the adult form because of the coexistence of vasculitis (inflammation of blood vessels), calcium deposits and defective metabolism of fat. In juvenile dermatomyositis, the skin lesions and weakness almost always occur at the same time, but the severity and progression of each symptom varies from patient to patient.

Inclusion body myositis mainly affects older individuals. The symptoms begin and progress slowly. Symptoms often are present for five to six years before diagnosis. Swallowing difficulties are noted in more than 20 percent of patients. As muscle weakness becomes severe, it is accompanied by muscle wasting and diminished deep-tendon reflexes. Unlike polymyositis and dermatomyositis, the muscle weakness is often not as symmetric, and may be prominent in the smaller muscles of the forearms and calfs.

How is it diagnosed?

To diagnose myositis, your doctor will ask you a series of questions about your symptoms, perform a physical exam and order several laboratory tests.

What are the treatment options?

Treatments can include rest, physical therapy and medications such as corticosteroids or DMARDS.