Archive Articles

Professor Gabriel Panayi

• Conference Report printed in Newsletter 35, Spring 1996 based on a talk given at the Myositis Support Group Conference 1995by Professor Panayi.

» Medical Papers
» Research



Conference Report printed in Newsletter 35 Spring 1996 based on a talk given at the Myositis Support Group Conference 1995 by Professor Panayi

The Nature of Myositis

This report summarised the main points made by Professor Panayi in his presentation to the Support Group in London in June 1995. He described the mechanisms which cause myositis both to start and to persist.

“Normal muscle has specialist muscle cells, blood vessels, nerves and supporting connective tissue. The normal muscle cells are of regular size and shape. The blood vessels have thin walls which act as filters and many components of the blood cannot leave the blood vessels and enter muscle. Normally there are very few inflammatory cells. During inflammation the blood vessels start to leak and constituents of the blood leave the blood vessel and enter the muscle. This includes the inflammatory white cells from the blood call lymphocytes. These changes characterise inflammatory muscle disease. There are three main types of inflammatory muscle disease; dematomyositis, polymyositis and inclusion body myositis and presents a distinct clinical picture.

The first change in dermatomyositis is seen in the muscle blood vessels which become inflamed and may be blocked, thrombosed or occluded. As a result nutrients do not enter that region of the muscle and as a result the muscle cells die whether they die partially or completely depends on the supply of oxygen and nutrients. The damage to muscle blood vessels is medicated by the combination of antibodies and complement, which are both components of the blood. Together they form “immune-complexes” which can cause damage to the surround tissue. There is uncertainty about which antibodies bind complement and cause damage to the blood vessels. This is an area of current research.

Lymphocytes are also involved in myositis. These are white blood cells and are not usually found in healthy muscles. There are T-lymphocytes which originate in the thymus gland in the neck. Normally, T-lymphocytes are involved in the body’s response to infections. Why these “T-cells” become activated and enter muscle, both in dermatomyositis and polymyositis, is a mystery. At present we have not idea why it occurs. The other type of lymphocytes are called B-lymphocytes and they make antibodies. These antibodies are often seen in damaged blood vessels in dermatomyositis.

There is a further subdivision of T-lymphocytes in two types. These are called CD-8 and CD-4 cells. They have different functions. In dermatomyositis the CD-4 lymphocytes, called helper T-cell, seem to be most important, these CD-4 cells activate the B-lymphocytes which mean they make antibody. The antibody present in the muscle then activates complement causing inflammation in the blood vessel and muscle damage. There are still many unanswered questions. We do not know why lymphocytes enter the muscle, nor do we know why they become activated.

Polymyositis is different and the blood vessels are not damaged in the same way as dermatomyositis. There are no deposits of antibodies and complement. T-lymphocytes are found but the main cell involved this time are the CD-8 cells. These are also called “killer cells” because they can kill other cells. These CD-8 lymphocytes are related to the dead and dying muscle fibres. Why should we have T-lymphocytes, developed in the thymus that are capable of killing cells of the body? The answer is two-fold. The first reason is that viruses when they invade the body live inside cells. The only way we can effectively get rid of viruses is by killing the virally infected cell. One crucial function of the CD-8 killer lymphocytes is to kill virally infected cells. The second function of CD-8 lymphocytes is to destroy tumour cells and CD-8 T-cells are also crucial to normal survival. Why do the CD-8 lymphocytes turn their armoury of killer molecules against muscle cells? Once again we don not know the answer to this and it an area for future research. One possibility is that the muscle cells may have been altered by a virus which has not yet been identified. There is some evidence that viruses can invade muscle cells and leave them open to destruction by killer cells, but we cannot be sure this is important in polymyositis.

The final type of myositis is called “inclusion body myositis”. This too has a distinct picture and is most like polymyositis [and inclusion bodies are present in the muscle]. There is less inflammation. Unfortunately it is especially difficult to treat this condition and we know less about it.”

<< Back to newsletters page