Sjögren syndrome (SS) is a systemic autoimmune disease that presents with sicca symptomatology of the main mucosa surfaces15. The main sicca features (xerophthalmia and xerostomia) are detected by specific ocular (Rose Bengal staining, Schirmer test) and oral (salivary flow measurement, parotid scintigraphy) tests. The histologic hallmark is a focal lymphocytic infiltration of the exocrine glands, determined by a biopsy of the minor labial salivary glands22. Patients with SS present a broad spectrum of serologic features (cytopenias, hypergammaglobulinemia, high erythrocyte sedimentation rate) and autoantibodies, of which antinuclear antibodies (ANA) are the most frequently detected, anti-Ro/SS-A the most specific, and cryoglobulins and hypocomplementemia the main prognostic markers34. The disease spectrum extends from sicca syndrome to systemic involvement (extraglandular manifestations)37.
SS is a heterogeneous disease that can be expressed in many guises17. The variability of its presentation may significantly delay the diagnosis after the onset of symptoms15. In addition, the epidemiologic characteristics, systemic involvement, or immunologic profile at diagnosis may have a significant influence on the presentation of SS. Researchers have analyzed these factors in various studies18,23,33,41 with differing results, which may be due to the small number of patients included and the different sets of classification criteria used. We conducted the current study to characterize the clinical presentation of primary SS in a large cohort of Spanish patients and to define epidemiologic, clinical, and immunologic subsets of patients with a more homogeneous expression in order to facilitate earlier diagnosis.
The GEMESS Study Group was formed in 2005 with the aim of collecting a large series of Spanish patients with primary SS, and included 12 Spanish reference centers with substantial experience in the management of SS patients. By March 2007, the database included 1010 consecutive patients, recruited since 1994, both incident and prevalent cases. Incident cases were classified as those diagnosed during the first study visit or within the previous 12 months. All patients fulfilled 4 or more of the preliminary diagnostic criteria for SS proposed by the European Community Study Group in 199344 and underwent a complete history and physical examination. Diagnostic tests for SS (Rose Bengal staining, Schirmer test, parotid scintigraphy, and salivary gland biopsy) were applied according to the recommendations of the European Community Study Group44. Clinical and laboratory data were collected and computerized according to a standard protocol designed by the GEMESS Study Group and based on previous multicenter studies17,35. Salient features included in the protocol were 1) age at diagnosis, defined as the age when the patient fulfilled the classification criteria; 2) age at inclusion, defined as the age when the patient was included in the registry; and 3) cumulative clinical and immunologic features during disease evolution (from the diagnosis until protocol inclusion). Exclusion criteria were chronic viral infections (negative test for anti-hepatitis C virus antibodies by ELISA), previous lymphoproliferative processes, and associated systemic autoimmune diseases defined according to previous studies17,30.
Definition of Clinical Features
Clinical features were defined as follows: Xerostomia and xerophthalmia were defined according to the European Community Study Group44.
Articular involvement included arthralgia (joint pain without inflammatory signs) and arthritis (tenderness, swelling, and/or joint effusion).
Raynaud phenomenon: intermittent attacks of digital pallor followed by cyanosis and/or rubor of the fingers, toes, ears, nose, or tongue, induced by exposure to cold, stress, or both, in the absence of any associated disease or anatomical abnormality.
Vasculitis was defined according to previous studies29. Vasculitides related to drugs, neoplasia, or infectious processes were excluded.
Lung involvement: persistent cough and/or dyspnea, with chronic diffuse interstitial infiltrates on X-ray, altered pattern on pulmonary function studies, and/or evidence of pulmonary alveolitis/fibrosis in computed tomography scans.
Nephropathy: persistent proteinuria >0.5 g/d, altered urinalysis (hematuria, pyuria, red blood cell casts), renal tubular acidosis, interstitial nephritis, or glomerulonephritis.
Pancreatic involvement: clinical signs of pancreatitis with raised levels of pancreatic enzymes.
Peripheral neuropathy: paresthesia, numbness, and/or motor defects of the lower/upper extremities confirmed by electromyography.
Involvement of the central nervous system (CNS): including demyelinating disorders, asymptomatic white matter lesions in magnetic resonance examination, and/or myelopathy.
Autoimmune thyroiditis: altered thyroid function with positive antithyroidal autoantibodies.
Lymphoma: histologic diagnosis of lymphoproliferative disorders was performed according to the World Health Organization (WHO) classification of tumors of hematopoietic and lymphoid tissues21.
Immunologic tests included ANA determined by indirect immunofluorescence using triple tissue cryostat sections (liver-stomach-kidney), precipitating antibodies to the extractable nuclear antigens Ro/SS-A and La/SS-B detected by ELISA, and rheumatoid factor (RF) detected by nephelometry. Serum cryoglobulins were determined as previously described42. Complement measurement consisted of the determination of C3 and C4 levels by nephelometry.
Categorical data were compared using the chi-square and Fisher exact tests. Continuous variables were analyzed with the Student t-test in large samples of similar variance and with the nonparametric Mann-Whitney U-test for small samples, with results indicated as mean ± standard error of the mean. A 2-tailed value of p < 0.05 was taken to indicate statistical significance. We compared the main cumulative, clinical, and immunologic SS data of the total cohort according to the following dichotomized variables: sex (male/female), age at diagnosis (< or > 35 yr, < or > 70 yr), incident/prevalent case, fulfillment of the 2002 criteria (yes/no)43, systemic involvement (presence of extraglandular features), and presence of immunologic markers (ANA, RF, anti-Ro/La, hypocomplementemia, and cryoglobulinemia). A multiple logistic regression analysis adjusted for age, sex, length of follow-up, and the variables that were statistically significant (p < 0.05) in the univariate analysis was performed. The statistical analysis was performed with the 12.0 SPSS program (SPSS, Chicago, IL).
The cohort consisted of 1010 patients, including 937 (93%) women and 73 (7%) men (female:male ratio, 13:1), with a mean age at diagnosis of 53.0 ± 0.48 years (range, 14-88 yr) and of 58.7 ± 0.46 years (range, 16-94 yr) at inclusion in the registry (Table 1). There were 233 incident cases and 777 prevalent cases, in whom the disease evolution ranged from 12 to 480 months (mean, 74.9 ± 4 mo). Nine hundred seventy-five (96%) patients had xerostomia; 968 (96%) had xerophthalmia; 269 (27%) had parotid enlargement; 898/956 (94%) had abnormal ocular diagnostic tests (Schirmer test and/or Rose Bengal staining); 580/759 (76%) had altered salivary flows and/or parotid scintigraphy; and 449/561 (79%) had a salivary gland biopsy showing lymphocytic infiltrates grade 3 or 4. The main extraglandular features were arthralgia in 490 (48%) patients, Raynaud phenomenon in 187 (18%), arthritis in 150 (15%), pulmonary involvement in 112 (11%), peripheral neuropathy in 110 (11%), vasculitis in 91 (9%), renal involvement in 48 (5%), CNS involvement in 21 (2%) and pancreatitis in 5 (0.5%). Two hundred eighty-seven (28%) patients had cytopenias, including anemia (18%), leukopenia (16%), and thrombocytopenia (13%). The main immunologic features were ANA ≥ 1/80 in 859/1005 (85%) patients, anti-Ro/SS-A in 518/1002 (52%), RF in 467/982 (48%), anti-La/SS-B in 343/1000 (34%), low C3 levels in 67/753 (9%), low C4 levels in 66/747 (9%), and cryoglobulinemia in 62/628 (10%).
SS in Men
Of the 1010 patients with primary SS, 73 (7%) were men. A lower frequency of altered ocular tests, positive ANA, Raynaud phenomenon, and thyroiditis was found in men compared with women in the univariate analysis. The adjusted multivariate analysis identified altered ocular tests (p = 0.004), Raynaud phenomenon (p = 0.025), autoimmune thyroiditis (p = 0.034), and ANA (p = 0.037) as independent variables (Table 2).
Age at Diagnosis <35 Years (Young-Onset SS)
In 137 (14%) patients, primary SS was diagnosed before the age of 35 years. A lower frequency of xerostomia, positive ocular tests, and thyroiditis and a higher prevalence of parotid enlargement, vasculitis, leukopenia, and immunologic markers (RF, anti-Ro/SS-A, anti-LaSS-B, low C3 and low C4 levels) were found in patients aged <35 years at diagnosis, compared with those aged >35 years in the univariate analysis. The adjusted multivariate analysis identified length of follow-up (p=0.002), xerostomia (p=0.008), altered ocular tests (p = 0.03), anti-Ro/SS-A antibodies (p < 0.001), low C3 (p = 0.018), and low C4 levels (p = 0.017) as independent variables (Table 3).
Age at SS Diagnosis >70 Years (Elderly-Onset SS)
In 156 (15%) patients, primary SS was diagnosed after the age of 70 years. A lower frequency of parotid enlargement, arthralgia, Raynaud phenomenon, and anti-Ro/SS-A antibodies and a higher prevalence of pulmonary involvement and anemia were found in patients aged > 70 years at diagnosis, compared with those aged < 70 years in the univariate analysis. The adjusted multivariate analysis identified length of follow-up (p < 0.001), arthralgia (p = 0.006), lung involvement (p < 0.001), anemia (p = 0.017), and anti-Ro/SS-A antibodies (p = 0.035) as independent variables (Table 4).
Long-Term Evolution (>10 Years)
Two hundred thirty-eight patients had an evolution of more than 10 years from diagnosis until inclusion in the registry. Compared with the incident cases, these patients had a lower mean age at diagnosis, a higher prevalence of xerophthalmia, positive ocular tests, anti-Ro/SS-A and anti-La/SS-B antibodies, parotid enlargement, arthralgia, vasculitis, lung involvement, peripheral neuropathy, leukopenia, and low C4 levels in the univariate analysis. The adjusted multivariate analysis identified age (p < 0.001), parotid enlargement (p < 0.001), lung involvement (p = 0.044), vasculitis (p = 0.047), peripheral neuropathy (p = 0.025), leukopenia (p = 0.008), anti-Ro/SS-A antibodies (p = 0.001), and low C4 levels (p = 0.036) as independent variables (Table 5).
Two hundred ninety-two (29%) patients presented only sicca symptomatology (without extraglandular features), while the remaining 718 (71%) presented a systemic process with diverse extraglandular manifestations. When SS patients were compared according to the presence of extraglandular involvement, those with a sicca-limited disease had a higher mean age at diagnosis and a lower frequency of parotid enlargement and immunologic markers (ANA, RF, anti-Ro/SS-A antibodies, and cryoglobulins) in the univariate analysis. The adjusted multivariate analysis identified length of follow-up (p = 0.003), ANA (p = 0.037), and anti-Ro/SS-A (p = 0.04) as independent variables (Table 6).
Fulfillment of the 2002 American-European Criteria
All diagnostic tests included in the 2002 criteria were performed in 766 patients: 707 (92%) fulfilled the 2002 criteria, and 59 (8%) fulfilled only the 1993 criteria. When SS patients were compared according to the criteria fulfilled, those who fulfilled only the 1993 criteria showed a lower prevalence of arthritis, pulmonary involvement, peripheral neuropathy, RF, and cryoglobulins in the univariate analysis, although only RF was statistically significant in the multivariate analysis.
Patients With Positive ANA
In comparison with ANA-negative patients, ANA-positive patients were more frequently female and had a lower mean age at diagnosis and a higher frequency of extraglandular features (Raynaud phenomenon, arthralgia, and arthritis), leukopenia, and positivity of other immunologic markers (RF, anti-Ro/SS-A, anti-La/SS-B antibodies) in the univariate analysis. The adjusted multivariate analysis identified arthralgia (p = 0.01), Raynaud phenomenon (p = 0.003), RF (p = 0.001), and anti-Ro/SS-A antibodies (p < 0.001) as independent variables (Table 7).
Patients With RF
Compared with RF-negative patients, RF-positive patients had a lower mean age at diagnosis and a higher frequency of positive salivary gland biopsy, parotid enlargement, extraglandular features (Raynaud phenomenon, arthralgia, arthritis, vasculitis, and CNS involvement), cytopenias (anemia and leukopenia), and positive immunologic markers (ANA, anti-Ro/SS-A, anti-La/SS-B antibodies, low C4 levels, and cryoglobulins) in the univariate analysis. The adjusted multivariate analysis identified vasculitis (p = 0.04), anti-Ro/SS-A antibodies (p < 0.001) and cryoglobulins (p = 0.006) as independent variables (see Table 7).
Patients With Anti-Ro/La Antibodies
In comparison with Ro/La-negative patients, Ro/La-positive patients had a lower mean age at diagnosis and a higher frequency of altered diagnostic tests (parotid scintigraphy and salivary gland biopsy), parotid enlargement, extraglandular features (Raynaud phenomenon, arthralgia, arthritis, vasculitis, renal involvement, and peripheral neuropathy), cytopenias (leukopenia and thrombocytopenia), and positive immunologic markers (ANA, RF, and cryoglobulins) in the univariate analysis. The adjusted multivariate analysis identified age (p < 0.001), parotid scintigraphy (p = 0.013), salivary gland biopsy (p = 0.013), Raynaud phenomenon (p = 0.014), peripheral neuropathy (p = 0.001), thrombocytopenia (p = 0.017), and RF (p < 0.001) as independent variables (see Table 7).
Patients With Hypocomplementemia
Compared with patients with normal C3/C4 levels, those with hypocomplementemia had a lower mean age at diagnosis and a higher frequency of extraglandular features (vasculitis), lymphoma, cytopenias (anemia, leukopenia, and thrombocytopenia) and positivity of other immunologic markers (RF and cryoglobulins) in the univariate analysis. The adjusted multivariate analysis identified the age at diagnosis (p < 0.001), vasculitis (p = 0.001), lymphoma (p = 0.01), and cryoglobulins (p < 0.001) as independent variables (see Table 7).
Patients With Cryoglobulinemia
In comparison with patients without cryoglobulins, those with cryoglobulinemia had a lower mean age at diagnosis and a higher frequency of parotid enlargement, extraglandular features (Raynaud phenomenon, vasculitis, renal involvement, and peripheral neuropathy), cytopenias (anemia, leukopenia, and thrombocytopenia), and positivity of other immunologic markers (RF, anti-Ro/SS-A antibodies, low C3 and low C4 levels) in the univariate analysis. The multivariate analysis identified parotid enlargement (p = 0.034), vasculitis (p < 0.001), leukopenia (p = 0.003), and low C4 levels (p < 0.001) as independent variables (see Table 7).
SS is a systemic autoimmune disease that affects mainly the exocrine glands and usually presents as persistent dryness of the mouth and eyes due to functional impairment of the salivary and lacrimal glands15. Although most patients present with sicca symptoms, SS is a disease that can be expressed in many guises, depending on the specific epidemiologic, clinical, or immunologic features. In the current study we evaluated the clinical and immunologic expression of primary SS in 1010 consecutive Spanish patients, the largest series analyzed to date, to our knowledge. We confirmed that, epidemiologically, primary SS is a systemic autoimmune disease that overwhelmingly affects women of middle age, with xerostomia, xerophthalmia, ANA, anti-Ro/SS-A, and RF being the most frequent features. However, several other manifestations not included in the current classification criteria such as arthralgia (48%), cytopenia (28%), parotid enlargement (27%), Raynaud phenomenon (18%), and arthritis (15%) were frequently found. These figures are similar to those found in the 2 largest reported series that we know of, from Greece20 (723 patients) and Sweden40 (484 patients).
The expression of SS in males was less pronounced than in females, and was characterized by a lower frequency of altered ocular tests and a lower prevalence of some extraglandular and immunologic features. All previous studies4,5,8,10,13,27,38 except one12 have described a lesser autoimmune expression (whether clinical, histologic, sialographic, and/or immunologic) in male patients. This is in line with one of the generally accepted ideas in autoimmunity, namely, that women have higher levels of autoimmune processes (both clinical and serologic) than men. Various reports have demonstrated this higher rate of autoimmune alterations in female patients, including a higher frequency of autoantibodies in healthy females16, higher levels of serum immunoglobulins9 and stronger humoral and cell-mediated immune responses14. These differences are especially marked in patients with autoimmune diseases characterized by B-cell hyperreactivity, such as systemic lupus erythematosus or primary SS32. This less-pronounced autoimmune expression in men may make early diagnosis of the disease difficult.
We found that the age at SS diagnosis plays a significant role in the clinical and immunologic expression of the disease. There was a specific pattern in the clinical expression of primary SS in young-onset patients (low degree of sicca involvement, high degree of systemic involvement). The identification of this specific presentation pattern may aid earlier diagnosis of these patients, in whom the diagnosis may be complicated by the less pronounced expression of sicca features. In addition, this subset of patients had a high frequency of immunologic features that may also facilitate the diagnosis. This confirms results in children and adolescents6,13 and other young-onset SS populations18,41. The clinical presentation of primary SS in elderly patients was diametrically opposite, with a lower prevalence of some systemic and immunologic features. This less pronounced autoimmune expression in older-onset patients may reflect senescence of the immune system36. However, no differences in the results of diagnostic tests (including salivary gland biopsy) were observed between older and younger patients, suggesting that the tests have the same diagnostic validity in older patients.
Positive autoantibodies are 1 of the 6 current classification criteria for SS and are the only analytical data included. The 1993 European Criteria44 include the presence of 1 or more of 4 antibodies (ANA, RF, Ro/SS-A, and/or La/SS-B), while the 2002 Criteria include only anti-Ro/SS-A and/or anti-La/SS-B antibodies43. ANA is the most frequently detected antibody in primary SS (85% in the current study), and is closely associated with various extraglandular and analytical SS features, as is RF, which was associated with the main extraglandular, histopathologic, hematologic, and immunologic SS features5,39,45. In light of this evidence, we believe that a patient with sicca syndrome, positive ocular tests and parotid scintigraphy, and positive ANA and/or RF should be classified as having SS, even when Ro/La antibodies are negative. ANA and RF determinations may play a central role in differentiating SS from nonautoimmune causes of sicca syndrome, and their role in the diagnosis of patients with suspected SS should be reconsidered. Our and other results suggest an important diagnostic role for ANA/RF determination and support their possible inclusion in future classification criteria.
The subset of patients with anti-Ro/La antibodies had the highest prevalence of most systemic, hematologic, and immunologic alterations, confirming previous reports in smaller series which found a close correlation between these autoantibodies and extraglandular manifestations2,3,11,19,28, serologic markers11,19,24,28, and a higher focus score in the salivary gland biopsy25,45. This suggests that anti-Ro/La antibodies should not be considered per se as a mandatory criterion for primary SS, since that characteristic identifies a specific subset of patients who probably have the most clinically and immunologically "active" SS presentation. The inclusion of positive anti-Ro/La antibodies as a mandatory criterion limits the diagnosis of primary SS, since some subsets, such as males, patients with late-onset SS, and those with sicca-limited disease, had a lower prevalence of anti-Ro/La antibodies, and therefore a lower probability of fulfilling the 2002 criteria.
The current study found a close association between hypocomplementemia/cryoglobulinemia and several epidemiologic, clinical, and immunologic features, such as a lower mean age and a higher frequency of vasculitis, lymphoma, and RF. Previous studies have prospectively confirmed that patients with hypocomplementemia and cryoglobulins at diagnosis have a higher risk of developing vasculitis and B-cell lymphoma during follow-up20,30,40. These studies also found that the presence of these immunologic markers at diagnosis have a key prognostic value in the survival of patients with primary SS. To our knowledge, Ioannidis and colleagues20 were the first to suggest the prognostic role of low C4 levels, and this was confirmed, together with low C3 levels, by Theander et al40. We have recently confirmed the prognostic role for low C4 levels at diagnosis and identified cryoglobulins as a new prognostic marker in primary SS. However, cryoglobulins, but not C4 levels, were independently associated with mortality in the multivariate analysis, suggesting that the negative association between hypocomplementemia and survival found in previous studies20,30,40 may be due to the complement activation caused by cryoglobulinemia. These data, all coming from large, prospective series of patients, confirm that complement and cryoglobulin measurement should be considered as the key immunologic markers in the follow-up of patients with primary SS (as complement and anti-DNA are for systemic lupus erythematosus), and their inclusion in the classification criteria of SS should be strongly suggested.
We found some differences in the main features of the current 1010 patients compared with those of the 400 patients described 7 years ago17. These included a higher frequency of xerophthalmia, parotid enlargement, articular involvement, and the main autoantibodies (ANA, RF, anti-Ro/La) (Table 8)1,20,40. Overall, the 4 studies have analyzed more than 2400 patients and have found similar percentages in Spanish, Swedish, and Greek patients, and provide a homogeneous view of the clinical and immunologic presentation of primary SS in Europe.
With respect to the characterization of the epidemiologic, clinical, and immunologic subsets of patients with primary SS, the adjusted multivariate analysis in the current study confirmed the majority of statistical differences found in the univariate analysis in our previous study of 400 patients. In addition, the multivariate analysis revealed new associations. First, we found an association between the age at diagnosis of SS and positive immunologic markers, with positive anti-Ro/La antibodies and low C3/C4 levels being more frequently found in patients diagnosed at a younger age. Second, we found a close association between cytopenias (leukopenia and thrombocytopenia) and both the length of SS evolution and the presence of anti-Ro/La antibodies and cryoglobulinemia. Finally, we confirmed the close association between hypocomplementemia, cryoglobulinemia, and lymphoma suggested by previous studies20,31,37,40.
The broad heterogeneity in the clinical and analytical features of patients with primary SS observed in the current study shows that our understanding of this systemic autoimmune disease is still evolving, and that the different criteria used for the diagnosis of primary SS lead to different visions of the disease. The 2002 criteria41, in which anti-Ro/La antibodies and/or positive salivary gland biopsy are mandatory, principally classify patients with the most pronounced extraglandular and immunologic expression. This subset of patients is easily diagnosed using these criteria, while patients with a predominantly sicca-limited disease, especially males, the elderly, and immunonegative patients, are excluded. As the current study and other recent studies have shown, the 2002 criteria do not cover the broad clinical and immunologic heterogeneity of primary SS, since 5 of the 6 criteria focus exclusively on glandular involvement and the remaining criterion is the mandatory presence of only 1 autoantibody, anti-Ro/SS-A (anti-La is overwhelmingly associated with Ro). In addition, the application of these criteria requires that all patients with negative Ro/La antibodies must be biopsied to evaluate if the criteria are fulfilled.
It may be time to re-evaluate the classification and definition of primary SS according to recent prognostic studies. Ioannidis and colleagues20 were the first that we know of to propose a prognostic classification of patients with primary SS according to the presence of low C4 levels and/or palpable purpura (type I and type II patients). Other and subsequent studies25,29,38 have confirmed the high risk of adverse outcomes in patients presenting with vasculitis or hypocomplementemia, and we have recently identified 2 additional risk factors (severe parotid involvement demonstrated by scintigraphy and cryoglobulinemia). Most of these recently described prognostic factors are not included in the current 2002 classification criteria, an additional reason for revisiting the diagnosis and classification of primary SS.
The authors thank David Buss for his editorial assistance.
The members of the GEMESS Study Group are listed below:
M. Ramos-Casals (Coordination), P. Brito-Zerón (Laboratorio de Enfermedades Autoinmunes "Josep Font," Servicio de Enfermedades Autoinmunes, IDIBAPS, Hospital Clínic, Barcelona); R. Solans, J. A. Bosch, M. Vilardell (Servicio de Medicina Interna, Hospital Vall d'Hebron, Barcelona); J. Rosas, G. Santos, R. Martín (Sección de Reumatología, Hospital de Villajoyosa, Alicante); A. Gil, P. Lavilla, I. Pérez (Servicio de Medicina Interna, Hospital La Paz, Madrid); M. T. Camps (Servicio de Medicina Interna, Hospital Carlos Haya, Malaga); J. Del Pino, C. A. Montilla (Servicio de Reumatología, Hospital Universitario de Salamanca, Salamanca); L. Pallarés (Servicio de Medicina Interna, Hospital de Son Dureta, Palma de Mallorca); J. Calvo-Alén (Sección de Reumatología, Hospital de Sierrallana, Torrelavega); M. L. Micó (Servicio de Medicina Interna, Hospital La Fe, Valencia); J. Beltrán (Sección de Reumatología, Hospital General de Castellón, Castellón); C. Hidalgo-Tenorio, J. M. Sabio, J. Jiménez-Alonso (Servicio de Medicina Interna, Hospital Virgen de las Nieves, Granada); R. Belenguer (Unidad de Reumatología, Hospital 9 de Octubre, Valencia).
1. Alamanos Y, Tsifetaki N, Voulgari PV, Venetsanopoulou AI, Siozos C, Drosos AA. Epidemiology of primary Sjogren's syndrome in north-west Greece, 1982-2003. Rheumatology (Oxford)
2. Alexander E, Arnett F, Provost T, Stevens M. Sjogren's syndrome: association of anti-Ro(SS-A) antibodies with vasculitis, hematologic abnormalities, and serologic hyperreactivity. Ann Intern Med
3. Alexander E, Provost T, Stevens M, Alexander G. Neurologic complications of primary Sjogren's syndrome. Medicine (Baltimore)
4. Anaya J, Liu G, D'Souza E, Ogawa N, Luan X, Talal N. Primary Sjogren's syndrome in men. Ann Rheum Dis
5. Asmussen K, Andersen V, Bendixen G, Schiodt M, Oxholm P. A new model for classification of disease manifestations in primary Sjogren's syndrome: evaluation in a retrospective long-term study. J Intern Med
6. Bartunkova J, Sediva A, Vencovsky J, Tesar V. Primary Sjogren's syndrome in children and adolescents: proposal for diagnostic criteria. Clin Exp Rheumatol
7. Brennan M, Fox P. Sex differences in primary Sjogren's syndrome. J Rheumatol
8. Brennan M, Sankar V, Leakan R, Kleiner D, Atkinson J, Wilkinson W, Baum B, Pillemer S. Risk factors for positive minor salivary gland biopsy findings in Sjogren's syndrome and dry mouth patients. Arthritis Rheum
9. Butterworth M, McClellan B, Allansmith M. Influence of sex in immunoglobulin levels. Nature
10. Cervera R, Font J, Ramos-Casals M, Garcia-Carrasco M, Rosas J, Morla R, Munoz F, Artigues A, Pallares L, Ingelmo M. Primary Sjogren's syndrome in men: clinical and immunological characteristics. Lupus
11. Davidson B, Kelly C, Griffiths I. Primary Sjogren's syndrome in the North East of England: a long-term follow-up study. Rheumatology (Oxford)
12. Diaz-Lopez C, Geli C, Corominas H, Malat N, Diaz-Torner C, Llobet J, De La Serna A, Laiz A, Moreno M, Vazquez G. Are there clinical or serological differences between male and female patients with primary Sjogren's syndrome? J Rheumatol
13. Drosos A, Tsiakou E, Tsifetaki N, Politi E, Siamopoulou-Mavridou A. Subgroups of primary Sjogren's syndrome. Sjogren's syndrome in male and paediatric Greek patients. Ann Rheum Dis
14. Eidinger D, Garrett T. Studies of the regulatory effects of the sex hormones on antibody formation and stem cell differentiation. J Exp Med
15. Fox R. Sjogren's syndrome. Lancet
16. Fritzler M, Pauls J, Kinsella T, Bowen T. Antinuclear, anticytoplasmic, and anti-Sjogren's syndrome antigen A (SS-A/Ro) antibodies in female blood donors. Clin Immunol Immunopathol
17. Garcia-Carrasco M, Ramos-Casals M, Rosas J, Pallares L, Calvo-Alen J, Cervera R, Font J, Ingelmo M. Primary Sjogren syndrome: clinical and immunologic disease patterns in a cohort of 400 patients. Medicine (Baltimore)
18. Haga H, Jonsson R. The influence of age on disease manifestations and serological characteristics in primary Sjogren's syndrome. Scand J Rheumatol
19. Harley J, Alexander E, Bias W, Fox O, Provost T, Reichlin M, Yamagata H, Arnett F. Anti-Ro (SS-A) and anti-La (SS-B) in patients with Sjogren's syndrome. Arthritis Rheum
20. Ioannidis J, Vassiliou V, Moutsopoulos H. Long-term risk of mortality and lymphoproliferative disease and predictive classification of primary Sjogren's syndrome. Arthritis Rheum
21. Jaffe ES, Harris NL, Stein H, Vardiman JW. World Health Organization Classification of Tumors. Pathology and Genetics of Tumors of Hematopoietic and Lymphoid Tissues. Lyon: IARC Press; 2001.
22. Kassan S, Moutsopoulos H. Clinical manifestations and early diagnosis of Sjogren syndrome. Arch Intern Med
23. Kraus A, Alarcon-Segovia D. Primary juvenile Sjogren's syndrome. J Rheumatol
24. Manoussakis M, Tzioufas A, Pange P, Moutsopoulos H. Serological profiles in subgroups of patients with Sjogren's syndrome. Scand J Rheumatol
. 1986; Suppl 61: 89-92.
25. Markusse H, Veldhoven C, Swaak A, Smeenk R. The clinical significance of the detection of anti-Ro/SS-A and anti-La/SS-B autoantibodies using purified recombinant proteins in primary Sjogren's syndrome. Rheumatol Int
26. Martens P, Pillemer S, Jacobsson L, O'Fallon W, Matteson E. Survivorship in a population based cohort of patients with Sjogren's syndrome, 1976-1992. J Rheumatol
27. Molina R, Provost T, Arnett F, Bias W, Hochberg M, Wilson R, Alexander E. Primary Sjogren's syndrome in men. Clinical, serologic, and immunogenetic features. Am J Med
28. Moutsopoulos H, Zerva L. Anti-Ro (SSA)/La (SSB) antibodies and Sjogren's syndrome. Clin Rheumatol
. 1990;9(1 Suppl 1):123-130.
29. Ramos-Casals M, Anaya J, Garcia-Carrasco M, Rosas J, Bove A, Claver G, Diaz L, Herrero C, Font J. Cutaneous vasculitis in primary Sjogren syndrome: classification and clinical significance of 52 patients. Medicine (Baltimore)
30. Ramos-Casals M, Brito-Zeron P, Garcia-Carrasco M, Font J. Sarcoidosis or Sjogren syndrome? Clues to defining mimicry or coexistence in 59 cases. Medicine (Baltimore)
31. Ramos-Casals M, Brito-Zeron P, Yague J, Akasbi M, Bautista R, Ruano M, Claver G, Gil V, Font J. Hypocomplementaemia as an immunological marker of morbidity and mortality in patients with primary Sjogren's syndrome. Rheumatology (Oxford)
32. Ramos-Casals M, Cervera R, Font J. Do male patients with primary Sjogren's syndrome have a higher frequency of autoantibodies? J Rheumatol
33. Ramos-Casals M, Cervera R, Font J, Garcia-Carrasco M, Espinosa G, Reino S, Pallares L, Ingelmo M. Young onset of primary Sjogren's syndrome: clinical and immunological characteristics. Lupus
34. Ramos-Casals M, Font J. Primary Sjogren's syndrome: current and emergent aetiopathogenic concepts. Rheumatology (Oxford)
35. Ramos-Casals M, Font J, Garcia-Carrasco M, Brito M, Rosas J, Calvo-Alen J, Pallares L, Cervera R, Ingelmo M. Primary Sjogren syndrome: hematologic patterns of disease expression. Medicine (Baltimore
36. Ramos-Casals M, Garcia-Carrasco M, Brito M, Lopez-Soto A, Font J. Autoimmunity and geriatrics: clinical significance of autoimmune manifestations in the elderly. Lupus
37. Ramos-Casals M, Tzioufas A, Font J. Primary Sjogren's syndrome: new clinical and therapeutic concepts. Ann Rheum Dis
38. Saito T, Sato J, Kondo K, Horikawa M, Ohmori K, Fukuda H. Low prevalence of clinicopathologic and sialographic changes in salivary glands of men with Sjogren's syndrome. J Oral Pathol Med
39. Shah F, Rapini R, Arnett F, Warner N, Smith C. Association of labial salivary gland histopathology with clinical and serologic features of connective tissue diseases. Arthritis Rheum
40. Theander E, Manthorpe R, Jacobsson L. Mortality and causes of death in primary Sjogren's syndrome: a prospective cohort study. Arthritis Rheum
41. Tishler M, Yaron I, Shirazi I, Yaron M. Clinical and immunological characteristics of elderly onset Sjogren's syndrome: a comparison with younger onset disease. J Rheumatol
42. Trejo O, Ramos-Casals M, Garcia-Carrasco M, Yague J, Jimenez S, de la Red G, Cervera R, Font J, Ingelmo M. Cryoglobulinemia: study of etiologic factors and clinical and immunologic features in 443 patients from a single center. Medicine (Baltimore)
43. Vitali C, Bombardieri S, Jonsson R, Moutsopoulos H, Alexander E, Carsons S, Daniels T, Fox P, Fox R, Kassan S, Pillemer S, Talal N, Weisman M. Classification criteria for Sjogren's syndrome: a revised version of the European criteria proposed by the American-European Consensus Group. Ann Rheum Dis
44. Vitali C, Bombardieri S, Moutsopoulos H, Balestrieri G, Bencivelli W, Bernstein R, Bjerrum K, Braga S, Coll J, de Vita S. Preliminary criteria for the classification of Sjogren's syndrome. Results of a prospective concerted action supported by the European Community. Arthritis Rheum
45. Wise C, Woodruff R. Minor salivary gland biopsies in patients investigated for primary Sjogren's syndrome. A review of 187 patients. J Rheumatol