Our A to Z of myasthenia
Acetyl-Choline (ACh) is a chemical transmitter released from nerve endings. It is far too small to be seen on any microscope.
Acetyl-Choline Receptor (AChR) is the ‘ignition lock’ on the nearby muscle surface. When ACh binds to it, it opens up channels into the muscles, allowing salt to enter and trigger the muscle into action. It can just be seen on the most powerful (electron) microscopes.
Acetyl-Choline Esterase (AChE) is a protein near the AChRs that destroys any spare ACh. Anti-choline esterases are drugs that block AChE, so that any ACh lasts longer and has a better chance of triggering. These drugs include pyridostigmine (Mestinon®) (long-acting), medium-acting neostigmine and Tensilon® (short-acting; edrophonium).
Antibodies are immune proteins tailor made to destroy germs or block toxins. They are made by ‘B cells’ (from the bone marrow) and travel around in the blood and tissue fluids.
Antibody negative MG is a bad name, because these people do have typical myasthenia-and it is caused by antibodies, but not against the AChR. In about half of them, antibodies instead recognise another muscle target called MuSK.
Apnoea/apnoeic attack is the sudden stopping of breathing. Auto-immune diseases are caused by cells or antibodies that can attack our own tissues or cell products.
Azathioprine (Imuran®) is a drug that generally suppresses immune responses.
B cell(s) are immune cells from the bone marrow. When their surface-bound antibodies recognise their particular target or germ, they release more of these antibodies to destroy it.
Bulbar applies to the movements of chewing, swallowing, speech and breathing controlled by the lower brain stem.
Congenital Myasthenic Syndrome strictly means myasthenia that can be seen at birth. In fact, some of these inherited faults in nerve to muscle triggering can start even in teenagers or adults. While many faults are in the AChR, others are in other genes involved in triggering.
Cyclophosphamide is a drug that generally suppresses immune responses. It is used in people who can’t take more standard immunosuppressants.
Cyclosporin A is a drug that generally suppresses immune responses, especially ‘T cells’.
DAP, ‘3,4 diamino-pyridine’ is a drug used to boost ACh release from nerve endings in LEMS and some congenital myasthenias.
Diplopia is double vision.
Diuretic is a drug causing an increased output of urine.
Dysarthria means to have difficulty in getting words out (in the movements of speech rather than in finding the right word in your brain).
Dysphagia is difficulty in chewing/swallowing.
Dyspnoea is difficulty in breathing.
Edrophonium (Tensilon®) is a very short acting anti-choline esterase drug.
EMG is short for electromyography. Nerves are stimulated electrically and the resulting electrical impulses are measured in the muscles they supply. EMGs help neurologists to sort out different congenital myasthenias and LEMS from immune myasthenia.
Firdapse® is a new form of DAP used to treat LEMS andsome CMS.
Imuran® see Azathioprine.
IvIg is short for intravenous immunoglobulin. This involves injecting (slowly into a vein) the pooled antibody fraction from normal blood. For unknown reasons this improves many auto-immune conditions.
LEMS, Lambert-Eaton Myasthenic Syndrome is caused by antibodies against nerve endings.
Mestinon® is the commercial name for pyridostigmine.
Methotrexate is a drug that generally suppresses immune responses and is used in people who can’t take more standard immunosuppressants.
Muscles are long tubes of proteins woven together; when triggered, they shorten (‘contract’). Thiscould be pulling bones (‘voluntary’ muscles), or narrowing tubes (the involuntary muscles in the guts, bladder, blood vessels and heart). Muscles and nerves are made up of huge numbers of much smaller cells.
MuSK is another target of antibodies in a few people with previously ‘antibody- negative’ myasthenia.
Mutation is an inherited fault in any gene.
Myasthenia is any form of muscle weakness.
Mycophenolate Mofetil is a drug like Cyclosporin A that generally suppresses immune responses, especially of ‘T cells’; also called CellCept®.
Neonatal myasthenia is the term used when myasthenia in a newborn baby is caused by antibodies from its mum. Luckily, it only happens with about one in eight myasthenia mums.
Neostigmine is another (medium-lasting) anti-choline esterase.
Nerves relay electrical impulses from sense organs (e.g. eyes and skin) to the brain and spinal cord or from there to muscles and glands. They relay the signals to other nerves or muscles at special junctions, and switch them either on or off. Some act more like dimmer switches telling things to work harder or slower.
Ocular myasthenia is myasthenia which only affects the eye movements not other muscles (nor eye focusing).
Plasmapheresis or plasma exchange means washing the liquid fraction out of the blood to remove the antibodies and then giving the red cells back in an artificial fluid.
Prednisone and Prednisolone are synthetic steroid drugs (like those from the adrenal glands) that generally suppress immune responses.
Propantheline is a drug like atropine that cuts down the side-effects of Mestinon® on the guts.
Quinidine is a drug that partly blocks the AChR, and is used to limit the harmful effects of some congenital myasthenias. It is related to quinine that comes from tree bark. This was used to treat malaria and is still an ingredient in tonic water.
Strabismus is a squint.
Synapse is any junction between a nerve and another nerve, a muscle or a gland. Signals can be passed either by chemical transmitters like ACh, or by direct electrical triggering.
T cells are immune cells from the thymus. Like antibodies, they also recognise foreign germs. They can either directly attack infected cells or recruit other cells to do that instead (‘inflammation’). They are also needed to help switch ‘B cells’ on.
Tensilon® (edrophonium) is a short-acting anti-AChE drug for diagnosing myasthenia. It is injected into a vein and the resulting increase in muscle strength is measured.
Thymus is a ‘factory’ that produces immune ‘T cells’, especially before age 40, and exports them to the rest of the body. It lies between the breastbone and the heart. It may be involved in starting the immune reaction against the AChR. A thymectomy (procedure to remove the thymus) seems to improve myasthenia in some young-onset people.
Thymoma is a tumour of the thymus found in around 10% of people with myasthenia. It may somehow auto-immunise in myasthenia.
Vaccine is a germ (or germ product) made harmless. ‘T and B cells’ still recognise it. It can be injected in advance. This stimulates these cells to multiply and forearm us before the real menace comes along.