A detailed view on salivary glands in primary Sjögren’s syndrome: histopathology and imaging

Primary Sjögren’s syndrome (pSS) is a systemic autoimmune disease characterized by dryness of the mouth and eyes. Besides the involvement of exocrine glands, multiple sites and organ systems can be affected. As pSS patients can present with a wide range of signs, diagnosing pSS can be complicated. The general aim of this thesis was to improve diagnosis and classification of the systemic autoimmune disease pSS by focusing on one of the main target organs: the salivary glands. The studies described in this thesis focused on salivary gland histopathology and salivary gland imaging. We showed that the addition of three histopathological features to the workup of salivary gland biopsies increased the diagnostic accuracy of the biopsy and also increased the specificity of the classification criteria. The three histopathological features are: presence of intraepithelial B-lymphocytes in striated ducts, a relative increase in IgG plasmacells, presence of germinal centers. Furthermore, we showed that ultrasonography of the parotid gland and histopathology of the parotid gland assess different (or at best partly related) constructs. Therefore, we concluded that ultrasonography cannot directly replace the salivary gland biopsy in the diagnostic work-up of pSS. Salivary gland imaging by using the nuclear medicine technique FDG-PET/CT currently has no place in the work-up of pSS, as it was not able to differentiate between salivary glands from pSS patients and salivary glands of two control groups. However, we showed that FDG-PET/CT imaging was useful to detect pSS-associated lymphomas and to detect systemic disease activity outside the salivary glands.