VARIABILITY OF QUANTITATIVE SCINTIGRAPHIC SALIVARY INDEXES IN NORMAL SUBJECTS

Several quantitative measures of salivary uptake and discharge have be en proposed recently in the scintigraphic evaluation of xerostomia. We investigated the scatter of four time-activity curve (TAC)-derived in dices in a group of volunteer subjects who met extensive inclusionary and exclusionary criteria of salivary normalcy, Methods: Thirty-one ad ult volunteers underwent dynamic salivary scintigraphy with gustatory stimulation. Any candidates with subjective xerostomia, conditions or medications associated with dry mouth, salivary gland enlargement or p regnancy were excluded from study. All subjects had normal oral exams, xerostomia scores and unstimulated whole-mouth salivary flow rates. A fter the intravenous administration of (TcO)-Tc-99m-4, scintigraphy wa s performed with generation of TACs derived from regions of interest c entered about the four major salivary glands and the oral cavity. At 4 5 min postinjection, hard lemon candy was given for 15 min as a gustat ory stimulus. The following functional indices were calculated for eac h gland: partitioned percentage (PP) of total prestimulated activity, maximum net uptake ratio (NUR) and its time of occurrence (T-NUR) and percentage stimulated discharge fraction (DF). Results: The following ranges were observed: parotid PP, 22%-49%; submandibular PP, 4%-31%; p arotid NUR, 2.2-16.0; submandibular NUR, 1.4-16.2; parotid T-NUR, 8-45 min; submandibular T-NUR, 2-45 min; parotid DF, 20%-99%; and submandi bular DF, 27%-98%, Every subject except one 91-yr-old man showed frequ ent periodic unstimulated oral transfer of salivary activity with a ri sing oral TAC and responded to gustatory stimulation. Conclusion: So-c alled quantitative indices may perform poorly in the scintigraphic eva luation of xerostomic patients because the effects of normal simultane ous glandular trapping, uptake, oral discharge and possible vascular w ashout combine to widen reference limits. Coordinated analysis of oral cavity and glandular activities, glandular index averaging and better temporal resolution may help improve diagnostic performance.