Quantitative Single-Photon Emission Computed Tomography/Computed Tomography for Evaluation of Salivary Gland Dysfunction in Sjögren's Syndrome Patients

Purpose

The purpose of the study was to investigate the usefulness of quantitative salivary single-photon emission computed tomography/computed tomography (SPECT/CT) using Tc-99m pertechnetate in Sjögren's syndrome (SS).

Methods

We retrospectively reviewed quantitative salivary SPECT/CT data from 95 xerostomic patients who were classified as either SS (n = 47, male:female = 0:47, age = 54.60 ± 13.16 y [mean ± SD]) or non-SS (n = 48, male:female = 5:43, age = 54.94 ± 14.04 y) by combination of anti-SSA/Ro antibody, labial salivary gland biopsy, unstimulated whole saliva flow rate, and Schirmer's test. Thyroid cancer patients (n = 43, male:female = 19:24, age = 46.37 ± 12.13 y) before radioactive iodine therapy served as negative controls. Quantitative SPECT/CT was performed pre-stimulatory 20 min and post-stimulatory 40 min after injection of Tc-99m pertechnetate (15 mCi). The %injected dose at 20 min and the %excretion between 20 and 40 min were calculated for parotid and submandibular glands, generating four quantitative parameters: %parotid uptake (%PU), %submandibular uptake (%SU), %parotid excretion (%PE), and %submandibular excretion (%SE). The most useful parameter for SS diagnosis was investigated.

Results

The uptake parameters (%PU and %SU) were significantly different among the SS, non-SS, and negative controls (p = 0.005 for %PU and p < 0.001 for %SU, respectively), but the excretion parameters (%PE and %SE) were not (p > 0.05 for both). The %PU and %SU were significantly lower in SS than in the negative controls and non-SS (p < 0.05 for all pair-wise comparisons). Additionally, the %SU was significantly lower in non-SS than in the negative controls (p < 0.05). Receiver-operating characteristic analysis revealed that the %SU had the greatest area-under-the curve of 0.720 (95% confidence interval = 0.618-0.807). Using the optimal cut-off value of %SU ≤ 0.07%, SS was identified with a sensitivity of 70.21% and a specificity of 70.83%.

Conclusion

Reduced submandibular uptake of Tc-99m pertechnetate at 20 min (%SU) was proved useful for the diagnosis of SS. Quantitative salivary gland SPECT/CT holds promise as an objective imaging modality for assessment of salivary dysfunction and may facilitate accurate classification of SS.

Salivary gland scintigraphy in Sjögren's syndrome: are quantitative indices the answer?

We evaluated the role of quantitative indices derived from dynamic 99mTc-pertechnetate salivary scintigraphy in the differentiation between a group of patients with Sjögren's syndrome (SS), a group of patients without xerostomia, but with underlying autoimmune disorders, and a group of controls. Seventeen patients with SS (group A), 18 patients with autoimmune disorders (group B) and 15 controls (group C) underwent dynamic salivary gland scintigraphy. Functional indices for the parotid and submandibular glands were calculated and comparisons were made between the groups. There were no significant differences between the three groups in terms of the maximum accumulation (MA), maximum secretion (MS) and pre-stimulatory oral index (PRI). The uptake ratios (URs) for both the right and left parotid glands and the left submandibular gland in group A were significantly lower than those in group C, but no different from those in group B. The URs for the parotid glands in group B were significantly less than those in group C. The percentage uptake by the right parotid gland at 4 min (U4) was significantly lower in group A than in groups B or C, and lower than the percentage uptake by the left parotid gland at 4 min in group A. The rest of the U4 values and all of the uptakes at 14 min (U14) were not significantly different between the three groups. The time taken for the right parotid gland to reach peak activity (Tmax) was significantly less in group A than in the other groups, but other glands showed no significant differences. It can be concluded that MA, MS and PRI cannot be used to differentiate between the three groups. The URs in groups A and B were no different, but were significantly lower than those in group C. However, the extensive overlap between xerostomic patients and normal controls for all the quantitative indices calculated imposes a severe limitation on their discriminatory power.