Prevalence of inflammatory back pain and radiologic sacroiliitis is increased in patients with primary Sjögren’s syndrome

Introduction The prevalence of Sjögren's syndrome (SS) in patients with the diagnosis of SpA has been reported to be higher than normal population. Yet, the vice-versa is unclear. In this study, we aimed to investigate the prevalence of IBP, radiologic sacroiliitis and SpA in patients with primary SS. Methods 85 patients followed at the rheumatology clinics of the Marmara and Kocaeli Universities with the diagnosis of primary SS between November 2011 and August 2012 were included in this study. The control group consisted of 100 age-and gender-matched patients. Inflammatory back pain and axial SpA were diagnosed according to the assessment of spondylo arthritis International Society (ASAS) criteria. Results 83 patients were (97%) female and 2 (3%) were male. Mean age of the patients was 49.1 (±11) years. Mean disease duration was 7.3 (±4) years. The patient and control groups were comparable in terms of age and gender (p > 0.05). Inflammatory back pain was observed in 21 (24.7%) of 85 primary SS patients and in 4 (4%) of 100 control subjects (p < 0.001), radiographic sacroiliitis was demonstrated in 9 (10.5%) of primary SS patients and 2 (2%) of the control subjects (p = 0.025). Remaining SpA findings were not encountered in either group. Conclusion inflammatory back pain and radiologic sacroiliitis is increased in patients with primary SS. Whether IBP, SI joint inflammation and radiologic sacroiliitis is due to the co-existence of SpA and primary SS or IBP is an underdiagnosed clinical feature of SS deserves further studies of large patient numbers.


Introduction
Sjögren's Syndrome (SS) is a systemic chronic inflammatory disease characterized by lymphocytic infiltration of exocrine glands [1].
Although dry eye and xerostomia due to the involvement of lacrimal and salivary glands are the major features of SS, other organ systems such as respiratory, urinary, neurological, gastrointestinal and hematological systems may be affected due to the involvement of related exocrine glands, as well [2][3][4]. Sjögren's syndrome is denoted as primary SS (pSS) when it exists solely and as secondary SS when it is associated with another autoimmune disease [5].
Rheumatoid arthritis (RA), systemic lupus erythematosus (SLE) and scleroderma are the most common autoimmune diseases associated with secondary SS [1][2][3][4][5][6]. Spondylarthropathies (SpA) comprise a group of inflammatory disorders, which are similar to each other in terms of clinical features and genetic susceptibility [7]. Ankylosing spondylitis (AS) is the prototype of these disorders and present particularly with inflammatory back pain (IBP) and radiologicallydetected sacroiliitis [8]. The prevalence of SS in patients with the diagnosis of SpA has been reported to be higher compared to control groups and population surveys in previous studies [9][10][11][12][13][14].
Yet, the vice-versa is unclear. No [16]. Firstly, all pSS patients were questioned for the presence of chronic back pain with at least three months of duration at any time before the age of 45. Patients were questionned using the following criteria: 1) Onset before the age of

Results
Eighty five primary SS patients and 100 control subjects were included in the study. The demographic characteristics of patient and control groups are presented in Table 1 Table 2).  Table 3).

Discussion
Sjögren's Syndrome occurring in association with SpA and/or AS has been reported previously [9]. However, IBP is not among the expected findings of SS. Coexistence of IBP and SS in a patient was first described by Chang et al who assessed this condition as an abnormal finding [10]. Afterwards, Golstein et al described 2 cases having SS and AS concurrently for the first time. Similar to the former case, they denoted this situation as in favor of a chance association [9]. Beyond those mentioned cases, there is a lack of elaborative investigations about the existence of IBP and SpA in primary SS patients. The prevalence of IBP and SpA was firstly evaluated in primary SS patients in our study, where the prevalence of IBP was 24.7% in the patient group, and 4% in the control group. These findings were comparable with the results reported by Weisman et al who found the prevalence of IBP to be 5 to 6% in healthy subjects in a relatively large cohort (n = 5013) [19]. When we compare criteria defining IBP, ASAS criteria have higher specificity (91.7%) than Berlin and Calin criteria, yet it has low sensitivity (77%). None of the criteria for IBP is adequate in terms of both specificity and sensitivity, we preferred to use ASAS, which has the highest specificity [16,20,21]. Despite the discrepancies between the underlying pathophysiological mechanisms, the association of SS with psoriatic arthritis, AS and reactive arthritis was reported by Whaley et al at 1971 [11]. Later, Di Fazone et al showed that SS European criteria was met more often in SpA patients compared to the control subjects (31% vs. 2.9%) in a study including 41 SpA patients and 102 control subjects [12]. sacroiliitis. In addition, in our study, the presence of IBP, radiologic sacroiliitis and axial SpA were investigated in primary SS patients who have been followed for a relatively longer period of time.
Sacroiliitis findings on radiological imaging develop nearly 5 to 10 years after the onset of IBP in almost half of the patients [22]. Therefore, although direct radiography assessed using modified New York criteria remains the initial imaging modality for detection of sacroilitis in the ASAS criteria, magnetic resonance imaging may be needed as second-line method of choice when modified New York criteria are not met [16]. Nine patients and two controls with IBP had radiographic sacroiliitis in our study. We therefore did choose to proceed with SI joint CTs instead of MRIs since an MRI is showed the superiority of CT scanning compared to direct X-ray in a study evaluating sacroiliitis in 17 symptomatic patients. While sacroiliitis was detected in 12 patients with CT, only 5 of these patients showed sacroiliitis on X-ray [26]. Similar results were found by Kozin et al in a study including 43 patients who had sacroiliitis clinically. 56% of the patients had sacroiliitis on CT scans; yet only 21% of the patients had suspicious findings on X-ray [24]. Beside these studies, Puhakka et al showed that both CT and MRI are equally sufficient in detection of sacriliitis [27]. Morover, CT has been found to be more useful and cheaper in demonstration of bone erosions, sclerosis and ankylosis in some studies [28][29][30].

Conclusion
In conclusion, inflammatory back pain and radiologic sacroiliitis is increased in patients with primary SS. Whether IBP, SI joint inflammation and radiologic sacroiliitis is due to the co-existence of SpA and primary SS or IBP is an underdiagnosed clinical feature of SS deserves further studies of large patient numbers.
What is known about this topic  The prevalence of Sjögren's syndrome in patients with the diagnosis of SpA is higher than normal population;  There is no sufficient data on the frequency of IBP and SpA in primary SS patients.

What this study adds
 Inflammatory back pain and radiologic sacroiliitis is increased in patients with primary SS;  IBP, SI joint inflammation and radiologic sacroiliitis is either due to the co-existence of SpA and primary SS or IBP is an underdiagnosed clinical feature of SS.

Competing interests
The authors declare no competing interests.