Salivary gland scintigraphy to detect chronic salivary gland damages after high dose radioiodine therapy for thyroid cancer: Correlation with sialography

Objectives To investigate whether salivary gland scintigraphy (SGS) is helpful to diagnose chronic salivary gland damages after high dose radioiodine therapy (RIT) for thyroid cancer.

Methods 56 patients with postsurgical thyroid cancer who received RIT underwent SGS in 2 - 4 yrs. after the latest therapy. Cumulative dose of I-131 ranged from 3.7 to 7.4 GBq. Of 56 patients, 25 had acute sialoadenitis after RIT while the remaining 31 did not had acute salivary injury. Scan images and time activity curves for the 4 major salivary glands were interpreted and were classified into 3 patterns: normal, obstruction dominant with preserved parenchymal function, parenchymal damage dominant with hypo or non-functioning gland. Patients who showed abnormal SGS finding further underwent sialography. Morphological changes in salivary ducts and parenchyma on sialographm were correlated with SGS. SGS was repeated 6-12 mos. after sialography.

Results 24 (44%) of 56 patients showed abnormal SGS findings, There were no significant difference in the frequency of abnormal SGS between patients with and those without acute salivary injury (48% vs. 42%, ns). Obstructive pattern and parenchymal damage pattern was observed in 13 and 7 pts., respectively. 4 patients had both patterns. On the sialogram, obstructive pattern was correlated with irregularity or narrowing in the lumen of the main duct or its branches. Degeneration or atrophy of the acinar lobe was correlated with parenchymal damage pattern. After cleansing of the ductal lumen, SGS finding improved in 8 (62%) of 13 patients with obstructive pattern but did not in any patients with parenchymal damage pattern.

Conclusions Obstructive pattern on SGS, which precedes parenchymal dysfunction, may be an early manifestation of chronic salivary gland damages after RIT. Xerostomia may be prevented if adequate therapy is planned at this stage. Once parenchymal damage pattern becomes evident, salivary dysfunction may be irreversible.