Jennifer, a healthy 27-year-old teacher, suddenly developed muscle weakness and pain in her arms and legs.  Because she was finding it difficult to reach with her arms or get out of a chair, she became worried and went to see her doctor.  Blood tests showed an elevated CPK of 5670 and an EMG (electromyogram) and muscle biopsy confirmed a diagnosis of polymyositis.  Her doctor started her on high doses of corticosteroids, followed by intravenous immunoglobulin infusion therapy, and her muscle weakness gradually improved. Because she was improving, her corticosteroids were decreased and then stopped, leaving her with the current treatment regimen of Methotrexate and physical therapy to increase muscle strength and endurance.

Polymyositis is an autoimmune disease, which occurs when our immune system attacks our own muscles, causing generalized muscle weakness, especially in the shoulders, upper arms, thighs, and hips, due to inflammation of muscle tissue.  It is estimated that only five out of every million people each year are diagnosed with polymyositis, so it is considered relatively rare.  Although men, women, and children can develop polymyositis, it seems to target women between the ages of 30 to 60.  Dermatomyositis, another autoimmune disease, has all the symptoms of polymyositis and a characteristic skin rash around the eyes, knuckles and hands.

Usually, the first symptom experienced with polymyositis is muscle weakness, making it difficult to lift your arms, comb your hair, or get out of a chair.  Its onset can be either gradual or quite sudden, and symptoms may vary from person to person.  Frequently, people experience muscle and joint paint, fatigue, and fever.  However, occasionally, shortness of breath or an irregular heartbeat can occur if the lungs or heart become affected.

CPK, an enzyme found primarily in our muscles, leaks into the blood stream when muscles are damaged or inflamed, thus creating an elevated level of CPK.  In general, the greater the muscle damage, the higher the level of CPK, as in Jennifer’s case.  Distinguishing whether or not the weakness is due to nerve or muscle damage can be revealed via an EMG, which measures the electrical activity within a muscle by inserting needle-like electrodes into muscles to stimulate and record their activity.  Finally, a muscle biopsy to examine muscle inflammation and damage under a microscope may be ordered to confirm the diagnosis.

Necrotizing myopathy (also called necrotizing autoimmune myopathy or immune-mediated necrotizing myopathy is unique form of autoimmune myopathy.  Necrotizing myopathy has unique findings on their muscle biopsies revealing histologically less inflammation but increased muscle cell death (necrosis) which distinguishes them from those with other forms of myositis.  Anti-signal recognition particle (anti-SRP) and 3-hydroxy-3-methylglutary-coenzyme A reductase (anti-HMGCR) are the two most common autoantibodies.

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).

Fortunately, over the past 20 years, the outlook of polymyositis and dermatomyositis has improved significantly, thanks to corticosteroids, intravenous gamma globulin, azathioprine (Imuran) and Methotrexate treatment to decrease inflammation and restore muscle strength.  Recently, clinical trials are studying the effects of biologic agents such as rituximab (Rituxan) on both polymyositis and dermatomyositis.  Along with medical treatments, physical therapy including various exercise programs is also vital to restore muscle strength and flexibility.