Radioactive Iodine and the Salivary Glands

Susan J. Mandel, Louis Mandel


Thyroid. 2003;13(3) 

In This Article

Salivary Gland Neoplasms and Strategies for Prevention

Because radiation can be carcinogenic, the incidence of salivary neoplasms after 131I therapy has been investigated. A small but statistically meaningful neoplastic increase years after 131I therapy has been demonstrated.[1,33,34] Reports include the development of pleomorphic adenoma,[35] non-Hodgkin's lymphoma,[36] and mucoepidermoid carcinoma.[37] Although definitive evidence is scant regarding neo-plastic change, its occurrence would seem to be in direct proportion to the dosage of 131I.

Rather than accept the salivary gland damage produced by 131I, the use of sour candy[1,4] or lemon juice[28] has been recommended to increase salivation during 131I administration in an attempt to reduce salivary gland damage. These interventions increase salivary flow and thereby decrease both the transit time of 131I through the parotid and the salivary 131I concentration. However, whether this results in a decrease in the overall salivary gland exposure to 131I is unknown. Transit time through the salivary glands can also be decreased with the cholinergic drugs pilocarpine or cevimeline using an empiric 5 day dosage regimen (2 days before, the day of and 2 days after 131I treatment). As a supplement, sugarless sour candy can be used at the time of treatment. Regrettably, there are no studies that have investigated the long-term efficacy of salivary stimulants (sour candy and/or cholinergic medications) in preventing salivary gland damage in patients receiving radioactive iodine. If medically possible, the temporary suspension of the use of any anticholinergic medications is also helpful.

Intravenous amifostine, an organic thiophosphate, is a recent addition to the drug armamentarium to combat the effects of irradiation.[38,39,40,41] Within the tissues, amifostine undergoes dephosphorylation to its active metabolite WR-1065. Alkaline phosphatase, present in all tissues, is necessary for this change. The conversion is more effective in the alkaline environment of normal tissue rather than the acid environment of tumor tissue. In addition, the concentration of alkaline phosphatase is 100 times greater in normal tissue than in tumor tissue.[33] Once the WR-1065 becomes available, it acts as a scavenger of oxygen-free radicals, which are the cause of radiation induced tissue damage.

A recent double-blind scintigraphic study examined the effect of amifostine on salivary gland function in 25 patients after amifostine infusion and 25 patients who received placebo prior to 131I therapy.[38] In conjunction with amifostine therapy, all 50 patients received salivary stimulation with ascorbic acid, and antiinflammatory therapy with an extremely high dose of dexamethasone (40 mg). One year after the 131I therapy, parotid and submandibular function was reduced by 40% in the placebo group and remained unchanged in the amifostine group. The one amifostine complication encountered was a decrease in mean blood pressure, which necessitated a temporary suspension of the infusion. Regardless of the safety record, there is some hesitancy to prescribe amifostine because many practitioners are not convinced that the amifostine does not inhibit the radioactive iodine's efficacy in the treatment of the cancer.

Patients should be made aware of the salivary gland damage that follows 131I therapy for thyroid cancer. The need for lifelong secondary prevention must be understood by the patient. Emphasis should be placed on the need to perserve salivary flow with glandular massage (Fig. 7) and to practice caution when anticholinergic drugs are used. Avoidance of any form of dehydration and the maintenance of an acceptable daily fluid intake must be impressed on the patient.

Although attention is legitimately directed toward achieving a cancer cure with the 131I, procedures should be implemented to negate the patient distress that is encountered from the radioisotope's harmful effect on salivary glands. The available techniques to prevent or diminish such injury should be part of the practitioner's knowledge base. In addition, early recognition and treatment of sialadenitis serve to lessen patient morbidity.


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