LAUSR

In our previous study, we found a rare type of medication-related osteonecrosis of the jaw (MRONJ), which shows periosteal reaction (PR) at a site distant from osteolytic lesions or the extraction site (periosteal reaction dominant type, PRd type), even though the osteolytic lesions in the bone marrow are localized. The causes and treatment of MRONJ remain unclear; hence, this study aimed to describe the imaging and clinical features of the PRd type. MRONJ patients who visited Nagasaki University Hospital between 2009 and 2020 and received conservative therapy as initial treatment were included in this study. The PR site, imaging findings, initial symptoms, outcome, and time to progression were examined. Among 59 MRONJ patients treated with conservative therapy, 38 did not show PR (PR− type), 15 showed PR near the osteolytic region (PR + type), and 6 had the PRd type. All patients with the PRd type had submental abscesses, and computed tomography (CT) images demonstrated PR on the lingual side of the anterior mandible. Osteolytic lesions progressed in 6/6 PRd type (100%), 5/15 PR + type (33.3%), and 2/38 PR− type (5.3%) patients. Time to progression for the osteolytic region on CT was short for the PRd type, at 56–148 days (median 79 days). Among the MRONJ types, the PRd type has a poor prognosis. Therefore, accumulating and analyzing more PRd cases in the future is warranted. This is the first report to describe the presence of this specific subtype of MRONJ.