Sjögren’s Syndrome (SS) is a chronic autoimmune disorder where the body’s immune system attacks moisture-producing glands, primarily the salivary and lacrimal glands, causing characteristic dryness symptoms. The disease is systemic and can also affect other organs, including the joints, lungs, and nerves. Ultrasound has emerged as a particularly valuable, non-invasive imaging tool in the management of this complex disease. The technique offers objective visual evidence of the structural changes caused by the underlying inflammatory process.
The Role of Ultrasound in Assessing Salivary Glands
Ultrasound is considered a preferred imaging method for evaluating the major salivary glands, offering a detailed view of the parotid and submandibular glands. This non-invasive procedure utilizes high-frequency linear array transducers, typically operating at 7 to 18 MHz, to generate high-resolution images of the glandular tissue. The examination involves applying a smooth probe coated with coupling gel to the areas over the angle of the jaw and beneath the mid-portion of the jawbone.
The primary advantage of salivary gland ultrasound (SGUS) is its ability to visualize the internal structure of the glands without requiring surgery or exposure to ionizing radiation. This makes it a cost-effective and repeatable option for patients suspected of having SS. Furthermore, SGUS can often serve as a reliable alternative to a minor salivary gland biopsy, which is an invasive procedure sometimes used to confirm the diagnosis.
The standard scanning protocol systematically assesses both the parotid and submandibular glands on both sides of the face. The goal is to detect structural abnormalities indicative of lymphocytic infiltration and glandular destruction characteristic of SS. The procedure is quick, typically taking only 5 to 10 minutes, and is well-tolerated by patients, making it suitable for routine clinical use.
Visualization allows clinicians to assess glandular size and the general texture of the parenchyma, or the functional tissue. Detecting structural changes early helps secure a diagnosis by providing objective evidence of glandular involvement. This physical evidence complements the clinical symptoms and laboratory blood tests traditionally used to classify and diagnose Sjögren’s Syndrome.
Interpreting Specific Ultrasound Findings for Diagnosis
The diagnosis of Sjögren’s Syndrome using ultrasound centers on identifying characteristic structural abnormalities within the salivary gland parenchyma. The most telling sign is glandular heterogeneity, which refers to an uneven or patchy texture of the gland. This irregularity results from the infiltration of lymphocytes, a type of white blood cell, into the glandular tissue.
These inflammatory infiltrates appear on the ultrasound image as hypoechoic or anechoic areas, meaning they are darker than the surrounding normal tissue. Hypoechoic areas generally represent clusters of inflammatory cells. Anechoic areas often correspond to small cystic lesions or ductal dilation caused by the ongoing inflammation. The presence, size, and distribution of these dark spots are directly linked to the severity of the inflammatory damage.
To standardize the interpretation of these visual markers, clinicians often use established grading systems, such as the Outcome Measures in Rheumatology Clinical Trials (OMERACT) scoring system. This system typically uses a four-grade scale, from Grade 0 (normal, homogeneous gland) to Grade 3 (severe, diffuse inhomogeneity). A higher score, particularly Grade 3 findings, strongly correlates with a positive result from an invasive labial salivary gland biopsy.
Changes in glandular size can also provide diagnostic clues. While the glands may be enlarged in the early, active inflammatory phase, long-standing SS often leads to glandular atrophy, resulting in smaller, shrunken glands. Furthermore, the presence of multiple hypoechoic lesions is associated with a higher likelihood of the patient testing positive for characteristic autoantibodies.
Beyond Salivary Glands: Assessing Other Manifestations
The systemic nature of Sjögren’s Syndrome requires assessment that extends past the major salivary glands, and ultrasound is increasingly employed to evaluate other affected anatomical sites.
Musculoskeletal ultrasound (MSUS) is routinely used to investigate joint involvement, which can manifest as inflammatory arthritis, a common extra-glandular feature of SS. MSUS allows clinicians to visualize soft tissue structures in detail, including the synovium, tendons, and joint fluid. The application of US can reveal objective signs of inflammation, such as synovitis (thickening of the joint lining) and joint effusion (excess fluid).
Ultrasound also plays an important role in monitoring for the risk of non-Hodgkin’s lymphoma, a serious complication of SS. Persistent or newly developed focal lesions within the salivary glands, or abnormal enlargement of local lymph nodes in the neck, can raise suspicion for lymphoproliferative disease. Ultrasound can guide a core needle biopsy directly into the suspicious lesion for definitive diagnosis of lymphoma.
Researchers are exploring the use of ultra-high frequency ultrasound to evaluate the lacrimal glands, which are the tear-producing glands. Similar to the salivary glands, the lacrimal glands in SS patients may show structural changes, including glandular heterogeneity and hypoechoic areas, reflecting lymphocytic infiltration. Lacrimal gland ultrasound holds promise for objective assessment of the dry eye component of the syndrome.
Using Ultrasound to Track Disease Progression
One of the most valuable applications of ultrasound in Sjögren’s Syndrome management is its capacity for longitudinal follow-up and tracking disease progression over time. Because the procedure is non-invasive and repeatable, it provides objective data that can be compared across sequential scans. This serial monitoring allows clinicians to assess the stability of the glandular damage or detect any worsening of the condition.
The established OMERACT scoring system facilitates this monitoring by providing a quantifiable measure of structural damage. By comparing scores from scans performed months or years apart, physicians can objectively determine if the disease is progressing to a more destructive stage. This information is important for guiding therapeutic decisions, especially concerning the initiation or modification of immunosuppressive treatments.
In addition to structural assessment, Power Doppler ultrasound is used to monitor active glandular inflammation. This technique measures blood flow within the tissue, and increased vascularity within the salivary glands indicates active inflammation. Power Doppler signals reflect the current level of immune activity, which is an immediate measure of disease activity, rather than long-term structural damage.
Ultrasound findings have been shown to be reversible in response to effective treatment. For example, sequential scans may show a reduction in the severity of hypoechoic foci and a decrease in the Power Doppler signals, signifying a successful reduction in glandular inflammation. This objective evidence provides a direct way to gauge the effectiveness of therapy and solidifies the role of ultrasound in the long-term management of Sjögren’s Syndrome.