Utilidad de la elastografía para la valoración de las glándulas salivales en pacientes con Síndrome de Sjögren Primario

Abstract

Sjögren's syndrome is a chronic autoimmune disease that affects salivary glands producing an inflammatory infiltrate that leads to glandular destruction, and thus to salivary deficiency and xerostomia. Within the imaging tests used in clinical practice for evaluation of salivary glands, ultrasound is of special interest, but although it is a reliable and non-invasive technique, it only offers qualitative results that must be interpreted and graded by the explorer, making this test highly subjective. Given this need to find an objective technique to add to conventional ultrasound to study these patients, ARFI elastography has been proposed as it allows the results to be standardized, by obtaining a numerical result, therefore adding reproducibility and improving its performance. Objective: The aim of the study was to validate ARFI elastography as a new technique to assess salivary gland involvement in patients with pSS, describing the elasticity of major salivary glands (parotid and submandibular) by measuring shear wave speed and comparing it with the findings in salivary glands of healthy subjects. Secondary objectives included the determination of a numerical cut-off point that allowed an appropriate diagnostic discrimination of patients with pSS from healthy subjects and the calculation of sensitivity, specificity and predictive values. The possible influence of the age of the patients and the years of disease evolution on shear wave speed values were also be studied. Methods: A case-control study was conducted, including 110 patients with primary Sjögren's Syndrome meeting the 2016 ACR/EULAR criteria and 110 age-matched subjects as a control group. An ultrasound examination of all four salivary glands was performed, obtaining images both in ultrasound B-mode and in ARFI elastography mode. After completing the exploration, ESSPRI and HADS for anxiety and depression questionnaires were completed. Demographic, clinical and laboratory variables were obtained from clinical records. Results: Mean shear wave speed and elasticity values were significantly higher in patients with pSS than in healthy subjects, this difference being statistically significant (p<0.05). In our study the mean elasticity of the shear wave speed mode was best able to differentiate the salivary glands of patients with pSS from those of healthy volunteers at a cut-off value for the mean of the four glands of 1,905m/sec, with a sensitivity of 95.5% and a specificity of 59.1%. This cut-off point has a positive predictive value of 70% and a negative predictive value of 92.9% (95% CI) with an area under the curve of 0.956 (95% CI 0.931-0.981). There was no statistically significant relationship between duration of symptoms, patient age or the degree of positivity of Ro and La autoantibodies and the elastographic results, so it could be considered an independent parameter. Similarly, the reproducibility of the test was confirmed with an intraclass correlation result of 0.953 (95% CI 0.949-0.988), not presenting significant variations in the intra-explorer result. Conclusion: ARFI elastography is a fast, reproducible, harmless, accessible and observer-independent ultrasound modality that allows an objective and quantitative evaluation of salivary gland stiffness in patients with pSS by measuring and analyzing shear wave propagation speed when passing through gland parenchyma. Our experience corroborates that patients with pSS present significantly higher values than healthy subjects in all salivary glands and that these values are not affected by the subject's age or by the years of disease evolution. Furthermore, the good sensitivity and specificity values obtained, allow us to establish EL as a technique of great clinical utility, not only as an aid to diagnosis by obtaining a numerical cut-off point that correctly discriminates healthy subjects from subjects with Sjögren´s syndrome, which would avoid the need for biopsy in selected cases, but also to determine the severity of glandular involvement from the onset, analyze disease progression or monitor the response to future treatments.