Appropriate utilization of semi-quantitative analysis in salivary scintigraphy

The purpose of this case-control study was to determine whether semi-quantitative indices derived from salivary time-activity curves (TACs) are useful in the diagnosis and management of xerostomia.

Twenty-six healthy volunteers and 83 consecutive patients with xerostomia, including a subset of 40 patients with Sjogren's syndrome, underwent sequential salivary scintigraphy (SSS). Semi-quantitative analysis of the TACs was performed, deriving six different indices, previously cited in the literature, for each patient. These reflected trapping and uptake, stimulated excretion, or stimulated and unstimulated oral radioactivity. The indices were the percentage uptake, uptake ratios, maximum accumulation, pre-stimulatory oral radioactivity index, post-stimulatory oral radioactivity index and ejection fraction.

Reduced parotid activity relative to submandibular activity, expressed as the P : S ratio, was able to distinguish abnormal from normal salivary function, and a parotid ejection fraction of greater than 50% also indicated normal parotid function. The other parameters showed no statistically significant difference between controls and patients. Individual variation in all indices served to widen the reference limits obtained from controls to the extent that they overlapped with those from the xerostomic population.

This finding, together with previous work indicating that uptake parameters are only sensitive to differences exceeding 25% of the gland mass, the possibility that xerostomia may result from qualitative as well as quantitative changes in saliva and the probability that immune factors decrease neurosecretory circuits without affecting acinar mass, suggest that those indices derived from salivary TACs that directly reflect trapping and uptake are not useful in the detection of salivary gland disease.