What is the significance of a focus score of ≥1 on a minor salivary gland biopsy in a patient with suspected seronegative Sjögren's syndrome?

Focus Score ≥1 on Minor Salivary Gland Biopsy in Seronegative Sjögren's Syndrome

A focus score ≥1 (defined as ≥1 focus of ≥50 mononuclear cells per 4 mm² of glandular tissue) on minor salivary gland biopsy is the mandatory diagnostic criterion for primary Sjögren's syndrome in patients who are seronegative for anti-SSA/Ro antibodies, and represents the histological hallmark that enables diagnosis when serological markers are absent. 1, 2

Diagnostic Significance in Seronegative Patients

The minor salivary gland biopsy becomes absolutely essential for diagnosis in seronegative Sjögren's syndrome because it is the only way to fulfill the 2016 ACR/EULAR classification criteria when anti-SSA/Ro antibodies are negative. 3 Without a positive biopsy showing focus score ≥1, seronegative patients cannot be classified as having primary Sjögren's syndrome regardless of their clinical symptoms. 3

Diagnostic Performance Metrics

The diagnostic utility of minor salivary gland biopsy in seronegative patients is exceptionally strong:

• Sensitivity: 93.3% - meaning the biopsy will correctly identify nearly all true cases of Sjögren's syndrome in seronegative patients 3
• Specificity: 100% - no false positives when focus score ≥1 is used as the criterion 3
• Positive predictive value: 100% - a positive biopsy definitively confirms the diagnosis 3
• Negative predictive value: 97% - a negative biopsy essentially rules out the diagnosis 3

These metrics demonstrate that the biopsy has superior diagnostic performance compared to clinical symptoms and signs, which have low specificity and positive likelihood ratios. 4

Technical Definition and Calculation

What Constitutes a Focus

A focus is defined as an aggregate of ≥50 mononuclear cells (predominantly lymphocytes) in a periductal or perivascular location, adjacent to normal-appearing acini. 1 Foci may be confluent and can include plasma cells, though the extent of plasma cell infiltration compatible with focal lymphocytic sialadenitis remains somewhat debated among experts. 1

Focus Score Calculation

The focus score is calculated by:

1. Counting the total number of foci in the entire specimen
2. Dividing by the glandular surface area (measured in mm²)
3. Multiplying by 4 to express as foci per 4 mm² 1

Critical technical point: The entire glandular surface area must be included in the denominator, including areas of atrophy, duct dilation, and fibrosis, to avoid introducing bias. 1 This standardized approach ensures reproducibility, though it may potentially reduce the focus score in late-stage disease with extensive fibrosis. 1

Upper Limit Considerations

Above a focus score of 10, foci are typically confluent, and a "ceiling" score of 12 may be applied. 1

Common Pitfalls and How to Avoid Them

Distinguishing from Non-Specific Chronic Sialadenitis

The most critical pitfall is misinterpreting non-specific chronic sialadenitis (NSCS) as Sjögren's syndrome. 1 Features of NSCS such as atrophy and duct dilation are common in the general population and may coexist with primary Sjögren's syndrome. 1

Key distinction: Focal lymphocytic sialadenitis cannot be attributed when the histological appearance is dominated by NSCS features (acinar atrophy, duct dilation, fibrosis) with no evidence of any foci adjacent to normal parenchyma. 1 However, given the prevalence of NSCS, some foci in Sjögren's syndrome may be expected adjacent to atrophic features. 1

Recommendation: The extent of atrophic features should be graded and reported to aid the referring clinician in interpretation. 1

Adequate Tissue Sampling

The biopsy must contain adequate glandular tissue for accurate assessment. 1 Insufficient tissue is a common cause of false-negative results. 5

Strict Application of Focus Scoring Criteria

Studies demonstrate that strict application of focus scoring guidelines significantly improves diagnostic accuracy. 5 When strict criteria were applied retrospectively, sensitivity increased from 80% to 95.4%, highlighting that initial interpretations may miss true cases due to inconsistent scoring methodology. 5

Additional Histopathological Features to Report

While focus score ≥1 is the primary criterion, other histopathological features should be documented as they increase diagnostic specificity and may have prognostic significance: 1, 6

Germinal Centers (Ectopic GCs)

The presence of germinal centers should be reported in routine practice. 1, 7 H&E staining is sufficient for detection by a histopathologist, though additional staining with CD21 (follicular dendritic cell marker), CD3, and CD20 can better define their presence. 1 Germinal centers are associated with increased lymphoma risk. 2

Lymphoepithelial Lesions (LESA)

Lymphoepithelial sialadenitis is characterized by lymphocytic infiltration of ducts with basal cell hyperplasia resulting in multilayered epithelium, and has potential prognostic significance for lymphoma development. 2 LESA is more commonly seen in parotid glands than in minor salivary glands. 2, 7

Enhanced Diagnostic Accuracy with Multiple Features

Recent evidence shows that including multiple histopathological features beyond focus score alone increases diagnostic accuracy by reducing false positives. 6 When an abnormal biopsy is defined by the presence of two or more features (focus score ≥1, pre-lymphoepithelial/lymphoepithelial lesions, IgG plasma cell shift, germinal centers) instead of focus score ≥1 alone, specificity increases from 84% to 95% for ACR/EULAR criteria fulfillment. 6

Clinical Context for Seronegative Patients

Approximately 10% of patients with clinically significant aqueous deficient dry eye have underlying primary Sjögren's syndrome, warranting a low threshold for biopsy when serologies are negative but clinical suspicion remains high. 2 Maintain high suspicion when dry eye occurs with systemic symptoms like fatigue, arthralgia, or recurrent parotid swelling. 2

The high proportion of cases with negative autoantibodies but positive focus score demonstrates the critical contribution of minor salivary gland biopsy to Sjögren's syndrome diagnosis in seronegative patients. 8 Without the biopsy, these patients would remain undiagnosed despite having genuine disease.

Prognostic Implications

Patients with focus score 4 (Chisholm score 4) may represent more established disease with higher autoantibody levels compared to those with focus score 3, though clinical findings remain similar. 8 The presence of additional features like germinal centers and LESA indicates increased risk for lymphoproliferative disorders, particularly extranodal marginal zone B-cell lymphoma of MALT type. 2