Effects of Radioiodine Treatment on Salivary Gland Function in Patients with Differentiated Thyroid Carcinoma: A Prospective Study.

Complaints of a dry mouth (xerostomia) and sialoadenitis are frequent side effects of radioiodine treatment in differentiated thyroid cancer (DTC) patients. However, detailed prospective data on alterations in salivary gland functioning after radioiodine treatment (131I) are scarce. Therefore, the primary aim of this study was to prospectively assess the effect of high-activity radioiodine treatment on stimulated whole saliva flow rate. Secondary aims were to study unstimulated whole and stimulated glandular (i.e., parotid and submandibular) saliva flow rate and composition alterations, development of xerostomia, characteristics of patients at risk for salivary gland dysfunction, and whether radioiodine uptake in salivary glands on diagnostic scans correlates to flow rate alterations. METHODS In a multicenter prospective study, whole and glandular saliva were collected both before and 5 mo after radioiodine treatment. Furthermore, patients completed the validated xerostomia inventory. Alterations in salivary flow rate, composition, and xerostomia inventory score were analyzed. Salivary gland radioiodine uptake on diagnostic scans was correlated with saliva flow rate changes after radioiodine treatment. RESULTS Sixty-seven patients (mean age ± SD, 48 ± 17 y; 63% women, 84% underwent ablation therapy) completed both study visits. Stimulated whole saliva flow rate decreased after ablation therapy (from 0.92 [interquartile range, 0.74-1.25] to 0.80 [interquartile range, 0.58-1.18] mL/min, P = 0.003), as well as unstimulated whole- and stimulated glandular flow rates (P < 0.05). The concentration of salivary electrolytes was similar at both study visits, whereas the output of proteins, especially amylase (P < 0.05), was decreased. The subjective feeling of dry mouth increased (P = 0.001). Alterations in saliva flow rate were not associated with semiquantitatively assessed radioiodine uptake in salivary glands on diagnostic scans. For the small cohort of patients undergoing repeated radioiodine therapy, we could not demonstrate alterations in salivary parameters. CONCLUSION We prospectively showed that salivary gland function is affected after high-activity radioiodine ablation therapy in patients with DTC. Therefore, more emphasis should be placed on salivary gland dysfunction during follow-up for DTC patients receiving high-activity radioiodine treatment.