Etiopathogenesis and laboratory diagnosis of shjogren syndrome
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"Sjögren's Syndrome"[MeSH Terms] AND diagnosis
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Sjögren disease laboratory diagnosis 2016 ACR EULAR classification criteria official
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https://pmc.ncbi.nlm.nih.gov/articles/PMC5650478/
Sjögren syndrome: etiopathogenesis and laboratory diagnosis
Sjögren syndrome, also termed Sjögren disease, is a chronic systemic autoimmune disorder in which lymphocytic inflammation predominantly damages the lacrimal and salivary exocrine glands. It may be:
- Primary Sjögren syndrome: occurring alone
- Secondary Sjögren syndrome: associated with another connective-tissue disease, especially rheumatoid arthritis or SLE
Etiopathogenesis
The precise initiating cause is not fully established. Disease results from interaction between a genetically susceptible host, environmental factors, glandular epithelial activation, and persistent dysregulated innate and adaptive immune responses.
1. Genetic and hormonal susceptibility
- Strong female predominance suggests a role for sex hormones and X chromosome-related immune regulation.
- Genetic associations include HLA class II alleles and variants influencing:
- Type I interferon signaling, such as IRF5 and STAT4
- B-cell survival, particularly the BAFF pathway
- B-cell receptor and immune-cell signaling pathways
- Genetic predisposition alone is insufficient. External triggers are thought to initiate autoimmunity.
2. Environmental or infective triggers
- Viral infections have been proposed as initiating factors, including Epstein-Barr virus and other viruses, but no single virus has been proven to cause Sjögren syndrome.
- Environmental stimuli may induce epithelial injury and release or abnormal display of intracellular self-antigens, especially Ro/SSA and La/SSB ribonucleoprotein antigens.
3. Epithelial-cell activation and innate immunity
Salivary and lacrimal gland epithelial cells are active participants, not just targets.
- Injured epithelial cells undergo apoptosis and expose autoantigens.
- Pattern-recognition receptor activation promotes production of cytokines and chemokines.
- A prominent type I interferon signature develops.
- Epithelial and immune cells produce BAFF (B-cell activating factor), promoting B-cell survival, autoreactivity, and autoantibody production.
4. T-cell-mediated glandular damage
- CD4+ T lymphocytes infiltrate the exocrine glands, chiefly around ducts.
- T-helper cell subsets, including Th1, Th17, and T-follicular-helper cells, stimulate inflammatory cytokine production and B-cell activation.
- Cytotoxic mechanisms and inflammatory cytokines cause acinar-cell dysfunction, loss of secretory capacity, and eventually atrophy and fibrosis.
5. B-cell hyperactivity and autoantibodies
B-cell activation is a central feature.
- There is polyclonal hypergammaglobulinemia and production of autoantibodies, particularly:
- Anti-Ro/SSA, directed against Ro52 and Ro60-associated antigens
- Anti-La/SSB
- Rheumatoid factor and ANA
- Persistent B-cell proliferation may produce ectopic germinal-center-like structures in salivary glands.
- This explains the increased risk of B-cell non-Hodgkin lymphoma, particularly MALT-type lymphoma.
6. Histopathologic end point
The characteristic lesion is focal lymphocytic sialadenitis: dense aggregates of at least 50 lymphocytes adjacent to otherwise relatively preserved acini. Progressive inflammation produces acinar destruction, reduced saliva and tears, xerostomia, and keratoconjunctivitis sicca.
Laboratory diagnosis
Diagnosis is based on clinical sicca symptoms and/or systemic features together with objective glandular tests, autoantibody testing, and sometimes labial salivary-gland biopsy. No single test establishes the diagnosis in every patient.
A. Autoantibody tests
| Test | Significance |
|---|---|
| Anti-Ro/SSA | Most useful specific serologic marker. It carries high diagnostic weight in current ACR/EULAR classification. |
| Anti-La/SSB | Supportive, usually occurs with anti-Ro/SSA. Isolated anti-La/SSB is not sufficient for current classification. |
| ANA | Common but nonspecific. A negative ANA does not exclude anti-Ro positivity, because assay methodology can miss some anti-Ro antibodies. |
| Rheumatoid factor | Common and supports B-cell activation but is nonspecific. |
| Anticentromere antibody | Found in a small subset and may indicate an overlap phenotype. |
Anti-Ro/SSA is the principal disease-associated antibody. Anti-La/SSB has supportive value, but isolated positivity should be interpreted cautiously. Textbook discussion notes that anti-La rarely occurs without anti-Ro and that assay format affects the detection of anti-Ro antibodies. Firestein & Kelley's Textbook of Rheumatology, p. 1572.
B. Nonspecific laboratory abnormalities
These support systemic autoimmune activity and help identify complications:
- CBC:
- Mild normocytic anemia, often anemia of chronic inflammation
- Leukopenia or lymphopenia
- Occasionally thrombocytopenia
- ESR: often raised, sometimes disproportionately high due to hypergammaglobulinemia
- Serum immunoglobulins: polyclonal hypergammaglobulinemia, chiefly raised IgG
- Rheumatoid factor: frequently positive
- Complement C3 and C4:
- Low C4 may indicate immune-complex activity, cryoglobulinemia, systemic disease, and higher lymphoma risk
- Cryoglobulins:
- Test in patients with purpura, neuropathy, renal involvement, low complement, or suspected lymphoma
- Renal work-up:
- Urinalysis, serum creatinine, electrolytes, bicarbonate
- Helps detect tubulointerstitial nephritis or distal renal tubular acidosis
- Liver tests and thyroid screening may be appropriate because autoimmune comorbidity can occur.
- Serum protein electrophoresis and immunofixation are useful when persistent gland enlargement, purpura, lymphadenopathy, unexplained cytopenia, or lymphoma is suspected.
Routine laboratory features can include leukopenia, raised ESR, hypergammaglobulinemia, ANA, RF, and anti-Ro/La antibodies. Harrison’s Principles of Internal Medicine, 22e, p. 3802.
C. Objective tests of ocular and salivary dysfunction
These are not serological tests, but they form part of the diagnostic laboratory evaluation.
| Test | Positive/abnormal result |
|---|---|
| Schirmer test | Tear wetting ≤5 mm in 5 minutes in at least one eye |
| Ocular surface staining | Ocular staining score ≥5 in at least one eye, or van Bijsterveld score ≥4 |
| Unstimulated whole salivary flow | ≤0.1 mL/min |
| Salivary gland ultrasonography | Supportive noninvasive test showing gland heterogeneity, hypoechoic areas, and architectural disruption. It is not currently a core 2016 ACR/EULAR item. |
D. Labial minor salivary-gland biopsy
This is particularly useful when anti-Ro/SSA is negative but clinical suspicion is high.
Diagnostic histology
- Focal lymphocytic sialadenitis
- Focus score ≥1 focus per 4 mm²
- A focus is an aggregate of 50 or more lymphocytes
Biopsy should be interpreted by an experienced pathologist. Nonspecific chronic sialadenitis, especially in older adults, may show fibrosis, duct dilatation, acinar atrophy, and mixed plasma-cell/lymphocyte infiltration but should not be mistaken for Sjögren histology. Firestein & Kelley's Textbook of Rheumatology, p. 1572.
E. 2016 ACR/EULAR classification criteria
For a patient with ocular/oral dryness symptoms or appropriate systemic features, classify primary Sjögren syndrome when the total score is ≥4, after excluding alternative causes.
| Item | Score |
|---|---|
| Labial salivary-gland biopsy with focal lymphocytic sialadenitis and focus score ≥1/4 mm² | 3 |
| Anti-Ro/SSA positivity | 3 |
| Ocular staining score ≥5, or van Bijsterveld score ≥4 | 1 |
| Schirmer test ≤5 mm/5 min | 1 |
| Unstimulated whole saliva flow ≤0.1 mL/min | 1 |
The original criteria study reported sensitivity of 96% and specificity of 95% in its validation cohort, as described in the ACR/EULAR criteria paper. Rheumatology, 2-Volume Set, p. 1307.
Important: These are classification criteria, mainly designed for uniform classification in research. In clinical practice, diagnosis still requires correlation with symptoms, objective findings, systemic manifestations, and exclusion of mimics.
F. Exclude important mimics before diagnosing primary Sjögren syndrome
- Drugs causing dryness, especially anticholinergic drugs
- Head and neck radiotherapy
- Active hepatitis C infection
- HIV/AIDS
- Sarcoidosis
- Amyloidosis
- Graft-versus-host disease
- IgG4-related disease
The ACR/EULAR framework specifically lists these as exclusions. Goldman-Cecil Medicine, p. 2478.
Practical diagnostic sequence
- Document dry eyes/dry mouth and systemic features.
- Test anti-Ro/SSA, anti-La/SSB, ANA, RF, CBC, ESR/CRP, immunoglobulins, complement, urinalysis, and targeted tests such as cryoglobulins.
- Obtain Schirmer test, ocular staining, and unstimulated salivary flow.
- If anti-Ro/SSA is negative or uncertainty remains, perform labial minor salivary-gland biopsy.
- Exclude mimics and evaluate for systemic involvement and lymphoma-risk features.
Current-evidence note
Recent systematic reviews indicate that salivary-gland ultrasound and ultrasound elastography are promising adjuncts, especially when biopsy is undesirable, but they do not replace anti-SSA testing or biopsy in the current ACR/EULAR framework. See ultrasound meta-analysis, PMID 38177085 and elastography meta-analysis, PMID 37658892.
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