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Imaging Procedures Useful for the Diagnosis of Sjögren’s Syndrome: Abnormalities of the Major Salivary Glands
Primary Sjögren’s syndrome (pSS) is an autoimmune disease affecting predominantly the salivary glands. Most of the classification criteria have considered involvement of salivary glands as a major sign of the disease. This involvement can be assessed by imaging procedures such as sialography or scialoscintigraphy (considered in the classification criteria currently used), which were the most commonly used procedures until 1990. More recently the development of magnetic resonance imaging (MRI) and ultrasonography (US) offers the opportunity to visualize specific abnormalities of major salivary glands using noninvasive and nonionizing procedures. Because of its easy accessibility and ability to save time in comparison with MRI, US appears to be the major imaging procedure used to classify Sjögren’s syndrome that has demonstrated its capacity to improve the diagnostic value of American-European Consensus Group (AECG) and American College of Rheumatology (ACR) criteria. MRI has value for complications such as duct obstruction, abscess, or lymphoma. Positron emission tomography/computed tomography (PET/CT) scan should be evaluated to detect nodal and extranodal location.
1
Sialography
1.1
Procedure
Sialography is based on the injection of a dye into the salivary duct orifice (Wharton or Stensen duct) in order to visualize the entire ductal pattern. It can induce discomfort for the patient, but the use of delicate catheters and gentle techniques can make the procedure painless. The sialograph is evaluated with panoramic, posteroanterior, or lateral views of the mandible. It has a great sensitivity to detect stone blocking of the duct. The presence of acute salivary gland infection and sialolithiasis of the duct, as well as allergy to contrast material, are contraindications for sialography. This procedure was commonly used until 1980 in Sjögren’s syndrome (SS). However, the development of sialoendoscopy for the treatment of salivary gland obstruction revitalized this radiographic technique.
1.2
Validity for Sjögren’s Syndrome
Sialography has been used for several years in SS and allows classification of patients with abnormal patterns, although sialographic changes in SS are not specific. The major excretory ducts can be normal but also atrophic with intraglandular diffuse collections that persist during the evacuation time of the procedure. Stages are described as normal with no contrast media collection or with punctuate, globular, cavitary, or destructive stages. The punctuated sialograph with sialectasias is considered as typical of SS. At a later stage, the cysts are enlarged and the gland is atrophic with complete destruction of the glandular parenchyma. Results of sialography correlated well with the diagnosis of SS, the presence of autoantibodies, or salivary gland biopsy (SGB) but appear to be less specific than labial SGB. Following these results, parotid sialography was included in the consensual classification criteria in 2002 and is considered abnormal if it shows diffuse sialectasias. However, this procedure is uncomfortable and can sometimes increase the sicca symptoms. Less invasive procedures, such as US, are now recommended.
2
Sialoscintigraphy
2.1
Procedure
Sialoscintigraphy is based on a scan after the injection of radioactive isotopes into the bloodstream ( Fig. 5.1 ). Technetium-99m is the most commonly used isotope, and is injected intravenously with simultaneous multiframe dynamic acquisition performed for 20–40 min. The scintiscan is considered for each gland using qualitative or quantitative analysis and evaluates the uptake, concentration, and excretion of the radioisotope by the major salivary gland with a gamma camera. The maximum uptake, the ratio between the mean counts in the gland at 20 min and the background activity and outflow efficiency can be calculated. Lemon juice stimulation can be performed for SS. It reveals the functional activity of the gland more than anatomical structures.
2.2
Validity for Sjögren’s Syndrome
The results of sialoscintigraphy, including delayed uptake, reduced concentration, and/or delayed excretion of tracer, are part of the 2002 classification criteria. The normal uptake of the radioisotopes in the salivary glands is diminished or patchy in SS, with a decrease in both excretion and uptake by the four glands. Most studies demonstrated its diagnostic accuracy with a good correlation with patient’s clinical symptoms of dryness, salivary flow rate, and sialography. Milic et al. evaluated its positive and negative predictive values (VVP and NPV), taking minor SGB as gold standard. She found VVP = 74.3% and VPN = 72.3%, and a good correlation with SGB or ultrasonography. Sialoscintigraphy has not been so extensively evaluated in SS as sialography and some uncertainty persists concerning the most useful parameters for detection of impaired parenchymatous function of major salivary glands.
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