Inflammatory myositis is the medical term for muscle inflammation. This causes the muscle to be weak and can also cause muscle ache and swelling. There are many types of inflammatory myositis but the major types include:
1. Dermatomyositis – in addition to muscle weakness, there is a rash on the skin especially around the eye-lids and the fingers. Cancer is found in approximately 10%-20% of cases. Sometimes, the muscle problem develops first. In other cases, the cancer is detected before the myositis.
2. Polymyositis – the condition affects the muscles alone without a rash. Cancer is not commonly associated with polymyositis, unlike in dermatomyositis.
3. Inclusion body myositis – the condition causes severe muscle weakness and wasting throughout the body over a long period of time.
4. Drug-induced myositis – the condition is triggered by the body’s response to a type of cholesterol lowering drug called statins. The symptoms of muscle pain and weakness can manifest over a short period of time, but patients can also improve rapidly once the medication is stopped.
Inflammatory myositis is a rare condition, affecting about 5 to 10 persons per million worldwide. While it can affect people of any age, there are two main clusters of patients: children between the ages of 5 to 15 years and adults between the ages of 30 to 65 years. Generally, women are twice more likely to develop myositis than men.
In dermatomyositis and polymyositis, weakness usually affects muscles near the centre of the body like the neck, shoulders and hips. Patients can experience difficulty with simple tasks like combing their hair, dressing, getting into a car, and standing up from a sitting position or climbing stairs. About one third or half of such patients also have problems swallowing and often choke when drinking fluids. Some patients with dermatomyositis and polymyositis also have lung involvement which results in cough and breathlessness.
General symptoms like lethargy, fatigue, weight loss and poor appetite are also very common
Other autoimmune diseases and a family history of inflammatory myositis may be risk factors.
Due to the many different forms of inflammatory myositis and similarities to other muscular and nerve diseases, it may take a few visits to the doctor before the condition can be diagnosed. After a careful physical examination, the doctor will order other tests to confirm the diagnosis. Such tests may include:
1. Routine tests like a full blood count, Erythrocyte Sedimentation Rate (ESR) and C-reactive protein (CRP).
2. Blood tests for muscle enzymes and auto-antibodies. Muscle enzyme levels (usually raised initially) are useful for monitoring progress and response to treatment.
3. Other Investigations:
• Electromyogram (EMG)This is a test that measures the electrical activity of muscles. In patients with inflammatory myositis the EMG would be abnormal.
• Muscle BiopsyThe doctor takes a sample of the affected muscle to be examined under the microscope. The procedure is done under local anaesthesia.
• X-ray of the chestTo investigate for lung cancer and lung involvement associated with inflammatory myositis.
• Magnetic Resonance Imaging (MRI)This painless scan can identify abnormal muscles and can be used to locate the best site for a biopsy and to monitor the progress of the disorder.
• A chest and abdominal CT scanThis test is useful to investigate for hidden cancers.
• Gastroscopy and colonoscopyThese tests are useful to investigate for underlying cancers in the gastrointestinal tract.
Although there is currently no cure for inflammatory myositis, it can be treated effectively so that patients lead healthy lives. Treatment strategies focus on alleviating symptoms and managing the progression of the condition. Compliance with treatment is very important.
For dermatomyositis and polymyositis, doctors usually start with high-dose corticosteroids (e.g. prednisolone) for about 4 to 6 weeks. When the condition improves the dosage is then slowly reduced. Other immunosuppressive treatments may be added (e.g. methotrexate).
Intravenous immunoglobulin (IVIG) (an injection of antibodies) may occasionally be effective in cases that fail the above first-line treatments. If IVIG is effective, it needs to be continued on a long term basis, although in lower doses to maintain the effect.
Another form of treatment in patients who do not respond well to conventional drugs is plasmapheresis or plasma exchange. This is a type of blood cleansing in which the damaging antibodies are removed from the blood. Often the effect is temporary.
In patients who are refractory to these treatments, intravenous rituximab (a monoclonal antibody which depletes B cells from the circulation) may be considered.
In patients with drug-induced myositis, the medication causing the inflammatory myositis will need to be stopped and replaced with an alternative. At the moment there is no effective treatment for inclusion body myositis.
Physical therapy and specially designed exercise programmes are very important for recovery of muscle strength.
3. Dermatomyositis associated with cancer
Treatment of the underlying cancer should take priority either by surgery, chemotherapy or radiotherapy.