What’s causing double vision on downward glance?

DEAR DR. ROACH » For two weeks, I have had double vision when I look down to the lower side. Each eye is individually normal, but I have double vision when using both eyes. An MRI was done by my doctor and was normal. Now my doctor suspects myasthenia gravis.

Please let me know whether it is curable or for life. Is treatment available?

— P.K.S.

ANSWER » My textbook lists over 70 causes of double vision on downward gaze. Many of these would cause an MRI result to be abnormal, but not all. Myasthenia gravis, a disease of the specific spot where the nerves interact with muscles (called the acetylcholine receptor), is a common cause of double vision in this situation. Your doctor will likely test you for antibodies to the acetylcholine receptor (or other closely related structures). The diagnosis may be confirmed by an electrodiagnostic study, which evaluates the function of the nerve/muscle junction.

If you do have myasthenia gravis, there are three kinds of treatments: symptomatic medical treatments, immunosuppression and surgery.

Pyridostigmine is a commonly used initial treatment for the symptoms of mild to moderate myasthenia. It stops the breakdown of the neurotransmitter — the chemical that the nerve uses to tell the muscle to fire — allowing for more effective muscle function. Some people do very well with this treatment, but it is minimally effective for others. Immune globulin and plasma exchange can be done in people with exacerbations of the disease.

Because MG is an autoimmune disease, suppressing the immune system can help control the course of the disease. This may be necessary for people who do not have a good response to pyridostigmine. Steroids are the usual first treatment. Other agents, such as azathioprine and mycophenolate, are used to improve effectiveness and reduce the many side effects of steroids. These take weeks to months to become effective.

Surgery on the thymus gland is indicated in people with a tumor of the gland, but may also can be recommended for people younger than 60 with antibodies to the acetylcholine receptor. The benefit of surgery takes effect slowly and improves over years.

Contact Dr. Roach at ToYourGoodHealth@med. cornell.edu.

Keith Roach