Disease targets connection between muscle and nerve

DEAR DR. ROACH: What can you tell me about myasthenia gravis? I’d like to know how it’s contracted, and what the treatment options are.

ANSWER: Myasthenia gravis is a disease of the connection between nerve and muscle. It is caused by an autoimmune process — meaning, the body mistakenly destroys one of the nerve/muscle receptors, which is how the nerve communicates information from the brain to the muscle.

The most common receptor is the acetylcholine receptor, but a smaller number of people with MG have antibodies to a different receptor, the muscle-specific tyrosine kinase. The thymus, an obscure organ in the neck (and the “T” of T-cells), may be the source of the autoimmune reaction.

The symptoms of MG are weakness and easily fatigued muscles, especially the muscles of the eye, which is where symptoms usually start. The muscle weakness comes and goes, and often people (or their friends) notice a drooping eyelid on one or both sides. Double vision is a common symptom.

There are many treatment options. Initially, many people with MG will be prescribed medication such as pyridostigmine (Mestinon). This keeps the acetylcholine in the synapse (the connection between the nerve and muscle) longer. In some people, it provides a dramatic benefit.

Medications used for other autoimmune diseases also are used in MG.

These agents — such as steroids, azathioprine and cyclosporine — suppress the immune system and reduce the destruction of the receptors, but increase the likelihood of infection. The antibodies can be removed with plasmapheresis, but the benefits last only a few weeks; this therapy is used for crises and if surgery is needed.

Finally, surgical removal of the thymus gland can improve symptoms and reduce medication need.

DEAR DR. ROACH: I am a 90-year-old man who has been diagnosed with macular degeneration. What treatments are available for this?

ANSWER: The macula is a part of the retina, the specialized bit of brain tissue in the back of the eye. There are two types of macular degeneration: proliferative (“wet”) and nonproliferative (“dry”).

Age-related macular degeneration is the leading cause of blindness in industrialized countries. In both types of macular degeneration, progression can be slowed down with vitamin supplementation, such as the AREDS formulation. (Current or former smokers should not take the standard supplement, as it contains betacarotene, which may increase lung cancer risk.)

In wet AMD, the most effective treatment is to inject medication into the eye that blocks growth of new blood vessels, such as bevacizumab (Avastin). Laser treatment used to be common, but is used much less often now.

Apart from the vitamin supplementation, there is no accepted effective therapy for dry AMD.