Polymyositis: symptoms, treatment and what to expect

Arthritis UK explains that myositis is the name for a group of rare conditions that cause muscles to become weak, tired and painful, and that the word simply means inflammation in the muscles. Polymyositis is one of the two most common types, along with dermatomyositis. "Poly" means many, so polymyositis means that many muscles are affected by inflammation.

Arthritis UK says polymyositis, dermatomyositis and the other types of myositis are autoimmune conditions: the immune system mistakenly attacks the body's own healthy tissue. Arthritis UK also notes that polymyositis does not often affect other parts of the body very much, whereas Myositis UK says it affects the muscles and connective tissues and sometimes the joints.

Myositis UK says the main symptoms are weak and painful muscles, tiredness and feelings of depression, and that some people also have joint pains. Most people notice muscle weakness within weeks, although some have the disease for months or even years before it is recognised.

• Weakness and tenderness in the large muscles around the hips and shoulders, which are usually the first to be affected.

• Difficulty walking, lifting the arms, or getting up from a sitting or lying position. Arthritis UK gives climbing stairs, brushing hair and getting in and out of cars as examples.

• Muscle pain, tenderness, and sometimes swelling, and a general feeling of being unwell.

• Weakness in the neck, making it hard to lift the head when lying down.

• Some trouble swallowing, and a voice that becomes nasal or deeper.

• Fever and weight loss in some people. Arthritis UK also lists night sweats.

• An increased tendency to fall, because of weak and tired muscles.

The types of myositis have overlapping muscle symptoms but differ in other features and in how they respond to treatment. Arthritis UK describes several types.

Arthritis UK says there is no single test that shows for certain whether someone has myositis. Your doctor will talk to you about your symptoms and examine you, and because the symptoms are similar to many other conditions you will probably have blood tests and other examinations. Myositis UK adds that experienced doctors will recognise myositis after a simple examination, and that it needs to be confirmed with blood tests and other tests.

• Blood tests: damaged muscles release enzymes such as creatine kinase (CK) and lactate dehydrogenase (LDH). Tests can also check inflammation levels and autoantibodies such as ANA, ENA and anti-Jo-1, though no antibody test proves myositis on its own.

• Electromyography (EMG): a fine needle electrode records the electrical activity of the muscle. Arthritis UK says it is not very painful but may be uncomfortable.

• Muscle biopsy: a small sample of muscle, usually taken under local anaesthetic, is examined under a microscope for signs of inflammation.

• MRI scan: can show where the inflammation is and areas of muscle replaced by fat.

Arthritis UK lists other conditions that can appear similar to myositis. Your doctor will think about these when assessing you.

• Side effects of some medicines, for example steroids and statins used to lower cholesterol.

• The effects of drinking too much alcohol over a long period.

• Hormonal conditions such as an under- or overactive thyroid.

• Low vitamin D, or abnormal calcium or magnesium levels.

• Infections, and other rare muscle conditions.

Myositis UK says that once the disease has been diagnosed, most people respond well to steroids, which are usually given in a high dose to begin with and then gradually lowered. Arthritis UK adds that steroids should reduce inflammation quickly and settle muscle pain, and that your doctor will reduce the dose as quickly as possible because high doses have side effects.

Sometimes symptoms flare up when the steroid dose is lowered. In that case, or alongside steroids from the start, a second medicine that suppresses the immune system is prescribed. Methotrexate, azathioprine, ciclosporin, tacrolimus and mycophenolate are examples. These need regular blood tests to check for side effects.

If these do not control the disease, Arthritis UK says cyclophosphamide, the biological therapy rituximab, or immunoglobulin infusions might be available. Myositis UK says most people will not need immunoglobulin.

Arthritis UK says it is probably best to rest when myositis is very active, but once it has calmed down regular exercise can greatly improve symptoms and overall health. Aerobic exercise is especially important to help restore muscle strength and improve stamina, and at first should ideally be supervised by a physiotherapist who will give you a tailored programme. Very strenuous exercise should be avoided.

Myositis UK says exercise is encouraged even in the early phases, guided by your doctor and physiotherapist, and that physiotherapy can help to maximise the efficiency of relatively unaffected muscles and help make weak muscles strong again.

Arthritis UK says people with myositis can make a good recovery and that even in severe cases most eventually respond to treatment, although you may need to try more than one treatment, and muscle strength can take longer to get back to normal. Some people never regain their original muscle strength or function, and many people need life-long drug treatment to keep the condition under control.

Myositis UK says a small percentage get well within two years, and for most it is a case of living with the condition. It says the disease is rarely fatal and that, as long as prescribed medication is taken, the future is hopeful. It also says there is always a possibility of a flare-up, including with hormonal changes in pregnancy, so medical advice should be sought before planning a pregnancy.

Arthritis UK says myositis can occasionally affect the muscles used for breathing and swallowing, which may happen at the start of severe cases, and on rare occasions can weaken the heart. Inflammation in the lungs can cause scarring that affects how the lungs work, and heart and lung conditions can cause long-term breathlessness, so you may be referred to a heart or chest specialist.

Polymyositis occasionally occurs in people who have other autoimmune conditions such as rheumatoid arthritis, lupus or scleroderma. On rare occasions myositis can be associated with cancer. Arthritis UK says most people with myositis do not develop cancer, but your doctor might arrange tests to be on the safe side.

Muscle weakness that is getting steadily worse, new difficulty swallowing or breathing, or a rapid change in strength needs prompt assessment, because the muscles used for breathing and swallowing can be involved. Contact your GP or specialist team the same day, call NHS 111 if you cannot reach them, and call 999 or go to A&E if you are struggling to breathe.

On the NHS, a GP usually refers you to rheumatology, neurology or a specialist myositis service, where blood tests, EMG, MRI and biopsy are arranged and treatment is started and monitored. Myositis UK notes that experienced doctors at a centre familiar with the disease will recognise it. Some people seek a private specialist opinion to speed up testing.