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Q & A

A Doctor’s View Newsletter 58, March 2005

• Does muscle weakness due to Myositis improve over time?
• Are there any new biological treatments for Myositis?
• What is an EMG test?

• What is Inclusion Body Myositis and can it be treated?
• There is a lot of interest in different diets. Can something specific like a gluten-free diet help?
• Sunlight can make me worse. What can I do about it?

A Doctor’s View Newsletter 58, March 2005

Does muscle weakness due to Myositis improve over time?

Muscle weakness is the feeling of lack of strength of one or more muscles. It can be subjective, when a person feels weak, but has no measurable loss of strength. It is usually objective, when there is measurable loss of strength. In Myositis weakness is almost always objective. It can be generalised, involving most of the body, or can be localised to one particular area or side of the body. In Myositis weakness is usually generalised. Many conditions cause weakness including metabolic disturbances, a range of neurological disease including strokes, toxicity from a range of exposures and muscle diseases such as Myositis. So weakness is a common problem that is characteristic but not diagnostic of Myositis. Inflamed muscles do not function normally and are weak. Therefore at the onset of Myositis weakness is very characteristic. Damaged muscles are also weak and so weakness can occur in the later stages of Myositis. The causes of weakness in active Myositis are complex. It may result entirely from direct damage to the muscles. But there are other changes such as reduced blood flow to the muscles that can starve them of oxygen - this is called tissue hypoxia. Associated with the weakness is fatigue, which can occur as a general response to the illness, similar to the fatigue of a flu-like illness. It can also occur as a result of damaged muscles recovering less well - local fatigue to the muscles.

In addition with illness people lose their overall physical fitness - they become deconditioned. This also contributes to the feeling of weakness. Treatment with immunosuppressive drugs and steroids will reverse the muscle inflammation. So patients with Myositis will become less weak due to this part of their disease. Damaged muscle cannot be renewed by normal tissue. But the existing muscle tissue can become stronger than previously. This improvement will overcome the feeling of muscle weakness.

Physical training in Myositis has two actions. First of all it improves the strength of existing muscles. Second it improves overall fitness. Both of these will reduce muscle weakness. In addition the feeling of muscle weakness is complex and has a subjective component. As we all age, we know that the strength of early adult life may have left us, but we do not feel weak. This is because we have adjusted our expectations. The same is partly true of the weakness of treated Myositis. Therefore although damaged muscles may never be entirely normal, for all practical purposes treating inflammation of the muscles and improving physical fitness by exercise in established disease will minimise the weakness of ongoing Myositis.

Are there any new biological treatments for Myositis?

New drugs are being developed all the time. They are mainly aimed at common diseases like rheumatoid arthritis. But they are then used in rarer diseases like Myositis in an exploratory way. In the last decade there has been an explosion in the number of biological treatments that have been developed. In rheumatoid arthritis one highly effective treatment is anti-TNF. This is an antibody treatment that inhibits one of the cytokines called tumour necrosis factor. Cytokines are the signalling molecules in our body. The name tumour necrosis factor simply reflects the first identification of the cytokine and says little about its function.

Anti-TNF is very effective in rheumatoid arthritis. It has two problems. First of all it is very expensive - about £10,000 annually for each patient. Second it damps down the immune system and leaves patients at risk of developing an infection. The balance of risks in severe rheumatoid arthritis favours these biologics, but each patient requires careful consideration and they need to be used with caution.

A small number of patients with Myositis have received anti-TNF treatments with mixed results. There are a few reports of impressive improvements. These are offset against reports of no improvements or major side effects. My personal view is that the risks currently outweigh the benefits.

Another biologic may give better results. This is called rituximab, which targets the antibody producing B cells in the body. It was developed to treat cancers of the B cells and is very effective in this role. It has also been used with considerable benefit to treat rheumatoid arthritis, though it is not yet licensed for this purpose.

There have been a few reports of patients with lupus and Myositis improving with rituximab treatment. The reasons for their improvements are not entirely clear. I am unconvinced that knocking out B cells and reducing antibody production is the only explanation. In any event it represents a hope for the future. At present it is no more than a possible treatment of last resort, because it is expensive and has many possible serious side effects. In the long term it will need a definitive trial to resolve its benefits and risks. But it suggests that there is the possibility of a new treatment avenue on the horizon.

An electromyogram, or EMG, tests the electrical activity in the muscles. It is usually undertaken by a neurophysiologist, who is one of a small number of highly specialised experts in the field of neurology. An EMG helps identify the causes of muscle weakness or paralysis and muscle problems such as twitching, numbness, tingling or pain, and nerve damage or injury.

Although they are safe, simple and risk free for patients, they are very difficult to interpret and always require an expert opinion. To me they seem almost uninterpretable, but an expert in the field has little problem. I always believe their interpretation is a mixture of science, art and experience.

An EMG relies on the fact that the activity of nerves and muscles produces electrical signals called action potentials. A nerve is actually a bundle of axons, cables that conduct action potentials from one end of a nerve cell to the other. The muscles are the recipients of these small electrical signals. In an EMG, the clinician inserts a small needle-like electrode into the muscle. This electrode records action potentials that occur when the muscle is at rest and during voluntary contractions.

The EMG shows whether a patient is likely to have Myositis, and can help to exclude nerve disorders and other associated muscle diseases. About 90% of patients with active Myositis have an abnormal EMG. It is important to test multiple muscles, as involvement can be limited. Healthy muscle appears quiet at rest. But spontaneous action potentials are seen in damaged muscles or muscles that have lost input from nerve cells. During voluntary contraction, dystrophic or wasted muscles show very small action potentials, and myotonic or stiff muscles show prolonged trains of action potentials. Altered patterns of muscle action potentials can indicate defects in nerve function.

The muscle fibres themselves are served by nerves that have cell bodies in the spinal cord. Each nerve branches several times and supplies a number of muscle fibres. The combination of a single nerve cell (called a motor neuron) and the muscle fibres it serves is called a motor unit. There are methods to study the electrical activity of these motor units individually using the EMG. As a non-expert in this highly technical field I would be unable to provide a useful commentary on the reporting of single motor units on the EMG. However, it is probably best to realise the limitations of knowledge. What is really needed is an expert opinion from a neurophysiologist. In many cases they will not say definitely yes or no, but they will provide an over view of the findings in muscles, which is invaluable in conjunction with other tests.

From the patients' perspective it involves a few needles being placed into the muscles and a lot of lying about in a relatively quiet room. It is safe and relatively time consuming - like so many aspects of life.

There is no standard course of treatment for IBM. The disease is unresponsive to steroids and immunosuppressive drugs. Intravenous immunoglobulin may have a slight, but short lasting, beneficial effect in a small number of cases. Physical therapy may be helpful in maintaining mobility. Other therapy is symptomatic and supportive. There is active research on whether biologics are helpful.

At the same time diet is important for us all. We need to avoid loosing weight when we are ill, and to avoid gaining weight when we are too inactive. Steroid treatment in myositis often increases weight, and this can be difficult to deal with. We also need to eat enough vegetables and fruit and try to keep to the five a day rule. This can be a tall order and we may not always get our diet exactly right. But a near miss is probably good enough.

Sunscreen can be used daily to dry skin about 15 to 30 minutes before going outdoors. Even on cloudy days up to 80% of UV rays still reach the earth’s surface. As repeated mini exposures to UV radiation accounts for most exposure daily use of sunscreens throughout the year is sensible.

Patients should avoid direct sun exposure, particularly during 10 AM and 4 PM especially during the summer months when the UV component of sunlight is least filtered through the atmosphere. Hats are sensible though unpopular. A wide brim hat is ideal. Sunscreens and sunblocks are essential. The sun protection factor is defined as the dose of UV radiation required to produce one minimal erythema dose on unprotected skin. This means the minimal sunburning dose. Some sunscreen products provide more UVA protection than others. Patients should select broad-spectrum sunscreens that contain agents that block UVB and UVA with an SPF of 30 or greater.

Finally you need to avoid sun-sensitising drugs. Some anti-inflammatory drugs or antibiotics are especially prone to causing sun-sensitivity and need to be avoided if possible. You will need to get advice from your doctor about specific drugs.

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