**5. Salivary gland disorders associated with radioiodine therapy**

Radioactive iodine (RAI) therapy is the most widely used treatment for differentiated thyroid cancer and has a long history. Because NIS is expressed in the salivary glands, 131I is also incorporated into the salivary glands. Not only thyroid cancer but also salivary glands are irradiated; and thus, acute/chronic sialadenitis may develop.

#### **5.1. Acute salivary gland disorders**

Sialadenitis is one of the most common adverse reactions to RAI therapy. Acute-phase sialadenitis causes swelling of the major salivary glands and pain (especially while eating) within one to a few days after oral administration of 131I. Although sialadenitis ameliorates without treatment, xerostomia may develop during the chronic phase and significantly impair the quality of life. Thus, when symptoms develop, sialadenitis should be treated immediately [16, 17]. The parotid glands may be affected more often than the submandibular glands. Steroids are more effective than nonsteroidal anti-inflammatory drugs. Cooling and frequent rinsing with cold water may relieve symptoms. Taste dysfunction is characterized by reduced acuity for salt taste and subsequently sweet taste; bitter taste remains unaffected. Taste dysfunction may become obvious later (2–4 weeks after 131I administration), rather than immediately after administration. To prevent an acute-phase disorder, snacks such as lemon candy to stimulate saliva secretion may be helpful because they also promote the excretion of 131I. Apitherapy using honey products is reportedly useful for preventing salivary gland disorders. Massage of the salivary glands and aroma therapy are also reported to relieve symptoms [18].

#### **5.2. Chronic salivary gland disorders**

Xerostomia may develop during the chronic phase, even in patients without acute impairment. Permanent dysfunction is reported to develop more frequently in the submandibular glands than in the parotid glands. Salivary gland scintigraphy shows a pattern of obstructive dysfunction before revealing parenchymal damage of the salivary gland. Therefore, salivary gland function may improve if salivary gland dysfunction can be identified within the period showing an obstructive pattern [19]. Salivary gland function should be monitored regularly with scintigraphy or other studies [20].
