Sjögren’s syndrome (SS) is a chronic autoimmune condition where the body’s immune system mistakenly targets the exocrine glands, primarily those responsible for producing moisture, such as the tear and salivary glands. This attack leads to the characteristic symptoms of dry eyes and dry mouth. To diagnose this condition, physicians often rely on a minor salivary gland biopsy, commonly referred to as a lip biopsy. This procedure provides a direct, physical assessment of the underlying immune-mediated inflammation.
The Procedure of the Minor Salivary Gland Biopsy
The minor salivary gland biopsy is a brief outpatient procedure typically performed by an oral surgeon, otolaryngologist, or rheumatologist. The patient receives a local anesthetic, injected into the inner surface of the lower lip, to numb the area. The lower lip is chosen because it contains a high concentration of small, easily accessible minor salivary glands, which mirror the inflammatory changes occurring in the larger, deeper major salivary glands.
A small, horizontal incision, usually between 5 millimeters and 1.5 centimeters in length, is made on the inside of the lip, away from the midline. The surgeon uses blunt dissection to locate and remove a cluster of minor salivary glands, aiming to collect a sample of at least four to six complete glandular lobules. The tissue samples are immediately preserved for pathological analysis.
After the glands are removed, the incision is closed with dissolvable sutures that typically disappear within one to two weeks. Patients may experience mild pain, swelling, or bruising for several days following the procedure, managed with over-the-counter pain relievers. A common, though usually temporary, side effect is localized numbness or altered sensation of the lower lip, which can last from a few weeks to several months.
Interpreting the Biopsy: Understanding the Focus Score
The collected minor salivary gland tissue is sent to a pathologist who examines the sample under a microscope for signs of focal lymphocytic sialadenitis. This specific finding is the hallmark of Sjögren’s syndrome and represents the body’s immune response within the gland tissue. The pathologist’s analysis centers on calculating the “Focus Score” (FS), which is the standard metric for a positive result.
A focus is defined as an aggregate, or tight cluster, of 50 or more inflammatory cells, specifically lymphocytes, gathered around a salivary gland duct or acinus. The Focus Score is calculated by determining the number of these distinct foci present within a standardized area of four square millimeters (4 mm²) of glandular tissue. The minimum requirement for a biopsy to be considered positive and supportive of an SS diagnosis is a Focus Score of one or greater (FS of 1 or greater).
The degree of inflammation is often graded beyond this basic score, with higher scores suggesting more extensive immune infiltration and glandular destruction. The presence of these specific inflammatory aggregates is considered a strong indicator of Sjögren’s, as it reflects the chronic autoimmune attack on the moisture-producing glands.
Defining Accuracy: Sensitivity and Specificity Rates
The lip biopsy has a high level of diagnostic accuracy, measured using two statistical concepts: sensitivity and specificity. Sensitivity refers to the test’s ability to correctly identify patients who truly have Sjögren’s syndrome. Specificity is its ability to correctly identify those who do not have the disease. Studies indicate that the biopsy’s sensitivity ranges from approximately 80% to over 90%, meaning it successfully detects the disease in most affected individuals.
The specificity of the lip biopsy is also high, often reported between 90% and 100% in many studies. A high specificity means that a positive biopsy result is highly reliable and is rarely seen in people without Sjögren’s, though false positives can occur in conditions like Hepatitis C infection or sarcoidosis. However, the biopsy is not without limitations, and false negative results can occur, primarily if the disease is in its very early stages before significant cellular aggregation has developed.
A false negative can result if the surgeon does not obtain an adequate number of glandular lobules, or if the sample is taken from a less inflamed area of the lip. Some patients confirmed to have Sjögren’s syndrome based on other criteria may still have a negative biopsy, especially if they are in the later stages of the disease where the glands have atrophied and the lymphocytic clusters have dispersed. The expertise of both the clinician performing the biopsy and the pathologist reading the slide also significantly influences the reported accuracy.
The Biopsy within the Full Diagnostic Criteria
Despite its high accuracy, the minor salivary gland biopsy is rarely used as the sole determinant for a Sjögren’s diagnosis. The current international classification criteria for the syndrome require a combination of findings to confirm the disease. The biopsy is categorized as one of the objective criteria, alongside specific blood tests and functional assessments of the eyes and salivary glands.
For a diagnosis, a patient must meet a weighted score based on a combination of these factors. The complementary blood work focuses on detecting specific autoantibodies, such as anti-Ro/SSA and anti-La/SSB, which are highly characteristic of the disease. Objective tests for glandular function include the Schirmer’s test, which measures tear production, and unstimulated whole salivary flow rate measurements.
The biopsy becomes particularly valuable in “seronegative” patients, who present with classic symptoms but test negative for the characteristic autoantibodies in their blood. In these cases, a positive Focus Score provides the necessary confirmation of autoimmune inflammation to complete the diagnostic criteria. While the procedure is generally safe, the potential for complications means the biopsy is reserved for cases where the diagnosis cannot be confirmed by less invasive means.