Salivary Function after Radioiodine Therapy: Poor Correlation between Symptoms and Salivary Scintigraphy

OBJECTIVE Symptoms of salivary gland dysfunction frequently develop after radioactive iodine (RAI) therapy, but have generally not been correlated with assessment of salivary gland functioning. The aim of this study was to determine whether there was a correlation between salivary symptoms and salivary functioning as assessed by salivary scan parameters. METHODS This was a non-randomized observational study. Fifteen patients receiving RAI therapy for differentiated thyroid cancer completed a questionnaire assessing their salivary and nasal symptoms prior to their therapy and 3 and 12 months after their therapy. Salivary gland scanning using technetium-99m pertechnetate was performed at the same time points. In addition, protective measures used at the time of radioiodine administration, such as use of fluids and sour candy, were also documented. Measures of salivary gland accumulation and secretion were correlated with scores of salivary and nasal symptomatology and any effects of protective measures were assessed. RESULTS The mean number of salivary, nasal, and total symptoms at 3 months increased significantly over the number of symptoms at baseline by 3.7, 2.7, and 6.3 symptoms, respectively (p values 0.001, 0.0046, and <0.001, respectively). The mean increases in the number of salivary, nasal, and total symptoms at 12 months were non-significant at 1.3, 1.3, and 2.5 symptoms, respectively. The mean right parotid gland accumulation and secretion of radioisotope declined significantly at 3 months, compared with baseline. The changes in left parotid and right and left submandibular function were non-significant. There was no association between the increase in salivary, nasal, or total symptoms and the change in scintigraphy measures. However, the increases in nasal and total symptoms were significantly greater in those with co-existent Hashimoto's disease, compared with those without this condition (p values 0.01 and 0.04, respectively). Nasal symptoms decreased (p value 0.04) and total symptoms trended to decrease (p value 0.08) in those who used sour candies, compared with those who did not. Increasing body mass index was significantly associated with increasing nasal symptoms (p value 0.05). Greater decline in salivary parameters at 3 months compared with baseline was generally associated with heavier body weight, decreased thyroid cancer stage, absence of Hashimoto's thyroiditis, and pre-menopausal status. CONCLUSION Salivary and nasal symptoms increased and salivary scintigraphy parameters decreased after radioiodine therapy. However, the increased symptoms did not correlate with decrements in salivary gland accumulation or secretion. Moreover, the variables associated with symptoms and changes in salivary scan parameters differed. Therefore, a better understanding of the relationship between salivary gland symptoms and functioning is needed. Factors affecting susceptibility to salivary and nasal damage after radioiodine therapy need to be better elucidated, so that modifiable factors can be identified.