Validity and Reliability of the Mastitis Symptom Severity Assessment Methods (M-Score and BISSI) in Non-Lactational Mastitis

Non-lactational granulomatous lobular/periductal mastitis (NL-GLM/PDM) are inflammatory breast diseases with unclear etiology, usually manifested as palpable breast mass, accompanied by breast pain and abscesses, erythema or fistula formation. There is no well-recognized assessment tool for evaluating the symptom severity and treatment efficacy of NL-GLM/PDM. In our previous studies with NL-GLM, we used the Mastitis-score (M-score) as a physician-directed measure of the symptom severity. However, there were no patient-reported outcome measure for NL-GLM/PDM. The Breast Inflammatory Symptom Severity Index(BISSI) was reported as a valid patient-reported outcome measure for lactational mastitis. Its clinical validity as a measure of Symptom Severity for NL-GLM/PDM are still unclear. In this multicenter, prospective cohort study, we will validate the validity and reliability of the M-score, a physician-directed measure, and the Breast Inflammatory Symptom Severity Index (BISSI), a patient-reported outcome (PRO) measure, for assessing symptom severity in patients with non-lactational granulomatous lobular/periductal mastitis (NL-GLM/PDM). Establishing the validity of these two approaches will facilitate the objective measurement of treatment efficacy for NL-GLM/PDM in the future.