Polymyositis is an uncommon disease that causes inflammation in your muscles. Doctors also refer to it as a type of connective tissue disease. Its most noticeable characteristic is muscle weakness, especially in the muscles closest to your trunk, such as your shoulder and hip muscles. As a result, you may find it difficult to get out of chairs, climb stairs, brush your hair or work with your arms over your head. The disease is rarely fatal, but it can be disabling in its more severe forms.
Although polymyositis can occur at any age, it mostly affects adults in their 40s and 50s. It is more common in blacks than in whites, and women have it more often than men do. The disease usually develops gradually over weeks or months.
A disease similar to polymyositis is dermatomyositis. Dermatomyositis leads to many of the same symptoms as polymyositis, but it causes a skin inflammation or rash as well. Globally, dermatomyositis and polymyositis together affect about 5 to 10 people out of 100,000. Other inflammatory muscle diseases include inclusion body myositis, which progresses more slowly than other forms; myositis associated with other connective tissue diseases, such as lupus or scleroderma; and myositis associated with cancer (malignancy).
Periods of remission, during which signs and symptoms improve spontaneously, rarely occur in polymyositis. However, treatment can improve your muscle strength and function.
Signs and symptoms
Signs and symptoms of polymyositis usually appear gradually, so it may be difficult to note when they first started. The most common signs and symptoms include:
Polymyositis belongs to a group of conditions called inflammatory myopathies. Myopathies are diseases or abnormal conditions of the striated muscles that cover your skeleton. The cause of most inflammatory myopathies is unknown. Doctors suspect that these are autoimmune disorders, in which your body's own immune system attacks itself. Infections caused by bacteria, parasites or viruses can cause inflammatory myopathies, but in most cases, doctors aren't able to identify an infection in polymyositis.
Typically, your immune system works to protect your healthy cells from
attacks by foreign substances, such as bacteria and viruses. If you have
polymyositis, an unknown cause seems to trigger your immune system to
begin producing autoimmune antibodies (also called autoantibodies). Many
people with polymyositis show a detectable level of autoantibodies in
their blood. It's unclear whether these autoantibodies are involved in
Polymyositis has also been associated with several viral diseases, including HIV. Some researchers speculate that, in some form, polymyositis may be caused by a viral infection of the muscle. This theory isn't well supported, however.
When to seek medical advice
If you experience weakness in your shoulder and hip muscles for a continued period, see your doctor. The earlier polymyositis is detected, the better your response may be to treatment. With treatment, you can manage and sometimes even reverse your signs and symptoms. If your doctor thinks you may have polymyositis, he or she may refer you to a specialist, such as a rheumatologist or a neurologist.
If you have difficulty swallowing or shortness of breath, call your doctor as soon as possible, as this may indicate the need for immediate help.