What are the implications of jaw pain near the temporomandibular joint (TMJ) in an adult patient with a history of papillary thyroid cancer, status post total thyroidectomy and high dose Radioiodine therapy, presenting 2 days after treatment?

Radioiodine-Induced Sialadenitis

This patient is experiencing radioiodine-induced sialadenitis affecting the parotid gland, a well-recognized complication occurring in approximately 25% of patients who receive high-dose RAI therapy (≥3700 MBq/100 mCi), with pain typically manifesting during salivary stimulation from eating. 1

Mechanism and Clinical Presentation

• The parotid glands concentrate radioiodine through sodium-iodide symporters, leading to radiation-induced inflammation and damage that manifests as pain during mastication when salivary flow is stimulated 1
• The 2-day timeframe post-RAI is consistent with acute sialadenitis, as the radiation effect on salivary tissue begins immediately after RAI uptake 1
• Pain localized to the TMJ region during eating is pathognomonic for parotid involvement, as the parotid gland lies directly over the mandibular ramus near the TMJ 1

Risk Factors in This Patient

• High-dose RAI therapy (used for papillary thyroid cancer post-thyroidectomy) is the primary risk factor, with damage occurring in 21% of patients receiving 3700 MBq (100 mCi) and increasing to 77.7% in those receiving ≥7400 MBq (≥200 mCi) 1
• Female patients have significantly higher risk (28.5%) compared to males (14.1%), making this a relevant consideration 1
• The bilateral parotid glands are most commonly affected (77 of 143 patients with damage had bilateral involvement), though unilateral presentation is possible 1

Diagnostic Confirmation

• Neck ultrasonography should be performed to assess for parotid gland abnormalities including diminished glandular volume, wavy contours, hypoechogenicity, and heterogeneity 1
• Physical examination should reveal tenderness over the parotid gland region, with pain exacerbated by palpation and during meals 1

Management Approach

• Immediate symptomatic management includes increased oral hydration (2-3 liters daily), frequent sour candy or lemon drops to stimulate salivary flow and clear radioiodine from glands, and NSAIDs for pain control 1
• Gentle massage of the parotid glands 4-6 times daily helps promote drainage and reduce inflammation 1
• Avoid dehydration and anticholinergic medications that reduce salivary flow 1

Critical Pitfall to Avoid

• Do not confuse this with TMJ disorder or dental pathology—the temporal relationship to RAI therapy and stimulation of pain specifically during eating (when salivary flow increases) distinguishes radioiodine-induced sialadenitis from musculoskeletal TMJ problems 1
• Recurrent laryngeal nerve injury would present with voice changes and hoarseness, not jaw pain during eating 2
• Hypoparathyroidism presents with perioral numbness and peripheral tingling, not localized jaw pain 2

Prognosis and Long-term Implications

• Most acute sialadenitis symptoms resolve within 2-4 weeks with conservative management, though chronic changes may persist 1
• Permanent anatomical damage (glandular atrophy) correlates directly with cumulative RAI activity, emphasizing the importance of using the lowest effective dose 1
• No injury was detected in patients receiving lower doses (1110-1850 MBq), highlighting that this complication is dose-dependent 1