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Patients who have received high dose radioiodine therapy may experience long-term problems with lacrimal gland function, reported Austrian researchers at the annual meeting of the Association for Research in Vision and Ophthalmology.
Radioactive sodium iodine therapy with I131 is commonly used to treat Grave’s disease and toxic nodular goiter. In thyroid cancer patients, however, radioiodine treatment is performed with higher doses.

Following oral administration, the iodine accumulates not only in the thyroid but also in other tissues including the lacrimal glands. While external radiation has long been known to affect the lacrimal glands, the long-term effects of oral administration have not been studied, noted Georg H Hanselmayer MD, Department of Ophthalmology, University of Vienna.

Dr Hanselmayer and colleagues conducted a cross-sectional study on the effects of oral high dose radioiodine therapy on lacrimal gland function. The study evaluated 182 eyes of 90 patients who had received radioiodine therapy from thyroid carcinoma.

The mean age of patients was 55 years, ranging from 17 to 81. All patients had received at least 2960 MBq 131-I (maximal administered activity 22.2 GBq 131-I). The protocol excluded patients with factors known to affect lacrimal gland function such as contact lenses and autoimmune disorders.

Dr Hanselmayer examined patients one to 317 months after radioiodine treatment (mean 64 months). He evaluated lacrimal gland function using three objective tests. He also obtained medical histories from the patients.
A comparison with age-matched controls showed significantly greater reductions in Schirmer’s tear test, break up time and lipid phase interference among treated patients.

Problems seen in majority of patients
The objective tests revealed that 70% of patients had at least one abnormal result, indicating impaired lacrimal gland function. Sixty-four patients had decreased tear film break up time (<5 sec) in at least one eye. Fifty-one patients had this result in both eyes.

Some 42% of patients showed decreased values by the Schirmer tear test in at least one eye while thirty patients manifested this in both eyes. A total of 18% of the study group demonstrated clearly abnormal Schirmer tests
(<5 mm/5 min). In addition, 39% of patients showed confirmed impairment of the lacrimal lipid in at least one eye.

Interestingly, the lacrimal function test results and clinical symptoms did not correlate with the total administered amount of radioiodine or with the time period since initial radioiodine treatment, he noted.

Previous research indicates that some 25% of patients receiving radioiodine therapy experience dry-eye symptoms within the first year of treatment. Dr Hanselmayer’s study is among the first to look at longer term effects.

Radioiodine therapy is employed to treat various forms of hyperthyroidism such as Grave’s disease and toxic nodular goitre. Successful treatment results in reduction or elimination of hyperfunctioning thyroid tissue leading to an euthyroid state. In these patients, radioiodine therapy is an excellent therapeutic option: side effects are rare, and the results are similar to thyroid surgery.

Thyroid cancer patients, however, reveal higher doses of radioiodine to eliminate remnant thyroid tissue after thyroidectomy. In these patients, side effects such as salivary gland or lacrimal gland dysfunction — reported by Dr Hanselmayer — may appear.

Dr Hanselmayer noted that further studies in patients with Grave’s disease and toxic nodular goitre will also be performed to evaluate a possible effect of lower amounts of radioiodine on the lacrimal glands.

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