**2. Diagnosis and Classification of pSS**

Currently, there is no "gold standard" test or diagnostic criteria set to support diagnosis of this heterogenous and multisystemic autoimmune disease [11,12]. Therefore, diagnosis of pSS is still based on expert opinion, which relies on interpretation of a combination of several assessments. Although there is no consensus yet which assessments are necessary for diagnosing pSS, the diagnostic work-up can consist of different items, such as clinical examination, serological tests, oral and ocular tests, imaging techniques, and histopathology of the salivary gland. In the past years, multiple classification criteria sets were developed for pSS. These classification criteria were developed for research purposes, to allow selection of well-defined and homogenous populations of pSS patients for clinical studies. However, the terms diagnosis and classification in pSS are often used interchangeably since diagnosis and classification depend on similar items/tests. Table 1 shows the items that are included in the various classification criteria sets. In this review, we focus on the value of imaging techniques in the diagnostic work-up of pSS. When we specifically discuss imaging techniques as items of classification criteria sets, we add the term classification.



ACR-EULAR: American College of Rheumatology-European League Against Rheumatism; ACR: American College of Rheumatology; AECG: American European Consensus Group; ESSDAI: EULAR Sjögren's Syndrome Disease Activity Index; UWS: unstimulated whole saliva; OSS: ocular staining score; vBv: van Bijsterveld score.
