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 of polymyositis usually appear gradually, so it may be difficult to note when they first started.