Thyroid Eye Disease and Smoking
Graves' thyrotoxicosis is caused by circulating antibodies that stimulate the thyroid gland to become overactive - hyperthyroidism. Graves' disease is the most common cause of thyrotoxicosis and about a quarter of patients also develop thyroid eye disease (TED).
The link between Graves' thyrotoxicosis and the eye
The antibodies that stimulate the thyroid can also attach and inflame the muscles that move the eyes. The eyes sit in a bony cup just large enough for the eye and the muscles and nerves - there's no extra space. If the muscles become inflamed the eye cannot expand though the bones, it can only go forwards, causing the eye to protrude, termed proptosis or exophthalmos.
Thyroid Eye Disease
The appearance can be distressing - the eye can be obviously pushed out, the white of the eye around the iris can be visible giving a staring appearance and the lid and conjunctive can become red and inflamed. As there is more of the eye out of the orbit both the tear film and the eyelid in blinking and in sleeping have more eye to cover This can cause the eye to feel dry or gritty during the day, and the eye can be uncovered at night; if the eye gets too dry it can be damaged and even ulcerate threatening vision. Furthermore as the eye is pushed forward the nerve at the back of the eye can be stretched and put under pressure from the swollen muscles, this can damage the nerve and threaten vision. Lastly the inflamed muscles do not always move as freely and if this limits the fine coordination of eye movements double vision can be the result.
Taken all together this is called Thyroid Eye Disease (TED) and/or Graves' ophthalmopathy, as part of extra-thyroidal Graves' disease. TED can occur at any time, before, during or even after the hyperthyroidism is diagnosed, but it does usually occur with the hyperthyroidism.
In most patients it is mild, but when it is severe it can be distressing and difficult to treat, requiring very close liaison between the endocrinologist, an ophthalmologist with experience of TED and the patient.
How is smoking relevant to TED and thyrotoxicosis?
Cigarette smoking is a major risk factor for the development and severity of TED. Indeed smokers have less chance of being cured of their thyrotoxicosis than non-smokers or ex-smokers. This may be because of the many chemicals in cigarette smoke but the reduction in oxygen availability to the tissues from smoking is also important.
TED is more common the more cigarettes one smokes but the good news is the risk declines very quickly if one stops smoking. If a patient has TED and continues to smoke the treatment is less effective, but again this difficultly quickly disappears if smoking stops.
Even exposure to passive smoke increases the risk of TED.
We do not yet know the effect of nicotine replacement therapy on TED, but if a smoker needs nicotine therapy to help them stop we think that it is appropriate to take the nicotine therapy.
Smokers with Graves' disease are about two times more likely to develop TED and heavy smokers are eight times more likely to develop TED.
If patients develops TED and they continue to smoke they are more likely to suffer the more severe forms of the disease than if they quit. These are 'proptosis' or 'exophthalmos' (protrusion of the eyeball), double vision due to squints developing and the most severe form which can cause blindness ('dysthyroid optic neuropathy').
If patients need any specific treatment for their eyes (such as steroids, radiotherapy or surgery), the treatment will not work as well if they continue to smoke because it seems that smoking makes them resistant to treatment and healing of tissues is slower and less complete.
Apart from the effects of smoking on the eyes of people with Graves' disease, smoking reduces the chance of a cure of the thyroid over-activity after a course of tablets because it is thought that smoking fuels the autoimmune attack on the thyroid and counteracts the effects of the medication.
General health can benefit if patients stop smoking.
Thyroid health and TED can improve significantly too.
Patients with Graves' Disease especially who already have Thyroid Eye Disease should stop smoking.
Your doctor will be very keen to support patients to stop smoking.