It has been widely established that women are more prone to develop autoimmune diseases [1]. Primary Sjögren’s syndrome (pSS) is a systemic autoimmune disease characterized by inflammation of the salivary and lacrimal glands, causing a reduction in exocrine secretion that ultimately leads to the clinical presentation of sicca symptoms. The reported population-based female to male ratio is 14:1 [2]. Many hypotheses have been proposed to explain the overall marked sex bias in autoimmunity and pSS [3], including genetic and epigenetic factors [4, 5], sex hormones [6], and X-chromosome aberrances [7, 8]. However, the molecular mechanisms that drive this sex skewing still remain elusive.

Interestingly, the differences between the sexes likewise extend to the clinical manifestations, where female and male patients differ in disease presentation and severity. Despite being less prone to develop autoimmune diseases, male patients have been reported to have a more severe disease and a worse prognosis. In systemic lupus erythematosus (SLE), men present more renal disease [9] and serositis [10]. Further, Andrade et al. [11] identified male sex as a strong predictor for poorer long-term prognosis due to accelerated damage accrual, while Manger et al. [12] reported male sex as a risk factor for increased SLE mortality. Male sex is also deemed as a factor for accelerated disease progression in multiple sclerosis (MS) [13] and associated with a significantly higher prevalence of comorbidities [14] such as diabetes, epilepsy, depression, and anxiety. Although less clear, sex differences in rheumatoid arthritis (RA) severity and extra-articular manifestations have also been described; women appear more prone to present sicca symptoms and men to have erosive joint disease, rheumatoid nodules, and interstitial lung disease [15, 16].

Regarding pSS, several studies have addressed sex differences in clinical presentation [17, 18]. As reviewed by Brandt et al. [3], some authors have identified differences in extraglandular manifestations and serological markers, with a focus on female prevalence. However, there is no clear consensus on whether male sex is associated with a more severe disease. Our group has described that at diagnosis, male patients more frequently present with extraglandular manifestations, more concomitant extraglandular manifestations, and higher anti-Ro52 levels by investigation in two independent cohorts [19]. To understand if there are sex differences in the clinical presentation of pSS also after a long-standing disease and whether risk for comorbidities vary between the sexes, we assessed glandular and extraglandular manifestations, serological parameters, and comorbidities of pSS in men and women years after diagnosis in a large Scandinavian cohort.

Primary Sjögren’s syndrome represents the autoimmune disease with the highest female bias, ranging from a ratio of 10–20:1 [22]. Besides the overwhelming sex bias observed in disease susceptibility, previous studies have also aimed to investigate whether the disease manifests differently between female and male patients. Earlier observations have not reached a clear consensus as to whether male pSS patients have a distinct clinical course and a more severe presentation of the disease [3]. In a recent study, though, we reported that men with pSS, from a population-based incident case cohort, displayed significantly higher levels of anti-Ro52, were diagnosed at an earlier age than their female counterparts, presented more concomitant extraglandular manifestations, and had a higher frequency of pulmonary complications and cutaneous vasculitis. Similarly, an Italian cohort revealed a significant male propensity towards extraglandular manifestation presentation [19]. These findings strongly suggest that men affected by pSS have a more severe disease at time of diagnosis. In the present study, we addressed whether differences between the sexes are also present several years after diagnosis.

We identified significant sex differences in terms of serological parameters and frequencies of some organ involvement. Our results indicate that the humoral response between women and men is different; particularly, men present more often with La/SSB, Ro/SSA + La/SSB and ANA positivity. This increased immune activity observed among the male patients is of special interest since in a healthy state, men mount a lower antibody response in comparison with women [23–25]. Although the pathogenic effect of autoantibodies has not been clearly established, the presence of certain autoantibodies has been associated with organ manifestations. Noteworthy, SSA antibodies are related to pulmonary diseases [26, 27], an extraglandular manifestation we observed overrepresented in the male patients from our cohort. Further, a recent study proposed that anti-La/SSB antibodies are a risk factor associated with increased mortality in pSS patients [28]. Thus, even though the pathogenic role of pSS-associated autoantibodies remains unknown, seropositivity has a strong correlation with organ involvement and worse prognosis, supporting the conclusion that the disease course is more severe in male patients than in female patients.

Interstitial lung disease has been extensively studied in the context of pSS [29, 30]. Male sex is widely recognized as a risk factor for developing interstitial lung disease [26, 31]. In accordance with more recent studies [19], our extended cohort shows that male patients with pSS are indeed more prone to develop interstitial lung disease. The reasons for this male preponderance are poorly understood; however, this might be due to increased seropositivity, environmental exposure to certain pollutants [32] and smoking [31] in the male pSS group. In fact, idiopathic pulmonary fibrosis, which represents a usual interstitial pneumonia histopathological pattern, is one of the most common forms of interstitial lung disease detected in pSS [29] and has a higher prevalence in men, as epidemiological studies have previously described [33, 34]. In other words, regardless of pSS diagnosis, men in general are more frequently affected by a type of interstitial lung disease that is associated with a worse prognosis. This susceptibility, thus, might be augmented in pSS, driven by other pathophysiological factors that enhance this propensity to develop pulmonary disease.

It is well known that pSS patients have an increased risk for developing non-Hodgkin lymphoma [35–38]. Sex-specific risk for lymphoma development in patients with rheumatic disease has been seldom studied, mainly due to the inclusion of mostly female patients. Nevertheless, Ansell et al. have reported a significantly higher incidence of lymphoma in male RA patients. Despite the increased association of autoimmune diseases and lymphoma in men [39], earlier studies of sex differences in lymphoproliferative malignancies in pSS have not shown a clear sex-specific predominance [40, 41]. In contrast, our present study is the largest pSS cohort to report a significantly increased risk for male patients to present lymphoma in comparison with female patients. This is in accordance with the results from a smaller patient sample from which an increased risk for men affected with pSS, SLE, RA, and autoimmune hemolytic anemia to develop lymphoma was reported [42].

Since the male bias observed in pSS-associated malignancies has only recently been described, it is not fully understood. However, considering the reported predictive factors of lymphoma development, an increased risk of lymphoma in male patients is logical. As reviewed by Nocturne and Mariette [43], the main clinical manifestations and parameters associated with this type of cancer are swelling of salivary glands, lymphadenopathy, palpable purpura, cryoglobulinemia, lymphopenia, low complement levels, and a monoclonal component in serum or urine. Interestingly, the male pSS patients from our cohort presented more frequently with lymphadenopathy. Although not included in the data analysis due to the high amount of missing data, cryoglobulinemia was also more commonly observed in the male patients (20/151 in females vs 3/7 in males, p = 0.03).

The only clinical manifestation that was more significantly represented in the female pSS patients from our cohort was hypothyroidism. Endocrine problems are not uncommon in patients with autoimmune disorders [44], and the female bias towards thyroid diseases has been extensively documented [45–48]. Furthermore, since the predominantly female incidence of hypothyroidism corresponds with the female susceptibility to autoimmune diseases, the thyroid gland has been proposed as a decisive organ to explain the sex skewness in autoimmune diseases. The effect of adipokines, which comprise a number of different cytokines including, e.g., leptins, adiponectins, TNF-α, and IL-6, on thyroid tissue has been suggested as a triggering mechanism for autoimmune thyroiditis, which probably precedes or coincides with the diagnosis of another systemic autoimmune disease such as pSS and SLE. [44]. This emphasizes the need for a comprehensive screening and close monitoring of thyroid function in suspected patients because it might be an important marker for autoimmune disease development. As for the thyroid gland being responsible for female-preponderant diseases, further studies should be performed to clarify its role.

The studied cohort offers a valuable large group of clinically carefully characterized patients with pSS, allowing for analysis of parameters that differ between men and women affected by the syndrome. The long follow-up time is essential for identifying clinical manifestations at different time points of the disease course. However, the patients included in this cohort were mostly included at tertiary referral centers of university hospital clinics. A possible limitation of the study is that the study population might therefore not mirror the general pSS patient population and that the patients described in this study represent cases with an overall more severe disease phenotype, both female and male patients. A further possibility is that male patients with mild symptoms and less severe disease are less often referred, as the primary health care doctor may not be as likely to suspect Sjögren’s syndrome due to its rarity in men, resulting in only men with more severe disease being included in the study. As the evaluation of extraglandular manifestations was dependent on doctors’ clinical assessments and did not include specific laboratory or physiologic tests unless the patient had symptoms, it is also possible that subclinical extraglandular manifestations may have been missed. However, the mean number of extraglandular manifestations diagnosed did not differ significantly between centers, nor did the proportion of men and women contributed. A further limitation is the lack of EULAR primary Sjögren’s syndrome disease activity (ESSDAI) and patient-reported (ESSPRI) indexes [49] at diagnosis, as well as information on other common extraglandular manifestations such as neurological diseases.

In summary, our findings provide compelling evidence that the clinical presentation of pSS differs between women and men. The sex-specific preference of some clinical manifestations hints at divergent pathophysiological mechanisms between women and men with pSS. Consequently, management of the disease will benefit from sex-specific tailored clinical programs to address complications that are common or expected in the respective sex.