Multiple myeloma identified within the same site of the mandible with medication-related osteonecrosis of jaw: An unusual case report

Multiple myeloma (MM) is a malignant disease characterized by abnormal proliferation of plasma cells, which usually occurs in middle-aged and elderly male patients. Bisphosphonates (BP) are commonly used for the treatment of MM bone disease. Long-time use of BP may cause medication-related osteonecrosis of the jaw (MRONJ). MRONJ occurs in jaw exclusively, and Multiple myeloma can also invade the jaw. The 2 diseases have similar clinical manifestations and imaging findings. This report present a case of MM identified in surgical specimen at the site that had been previously pathologically diagnosed as MRONJ in a patient with MM. PATIENT CONCERNS: A 57-years-old male patient visited our clinic on October 16, 2020 because of gingival swelling and pain in the right mandible for 1 month after extraction of the lower right premolar. The patient had a long-time illness history of multiple myeloma, and received intravenous zoledronic acid treatment. DIAGNOSES: Based on the clinical characteristics, imaging, and pathological findings of sequestrum formation and high inflammatory cell infiltration, the patient was diagnosed with MRONJ. After 1 year, a mandibular osteotomy was performed and pathological analysis showed the presence of necrotic bone and a large number of abnormal plasma cell infiltration, suggesting the presence of MM in the mandible. INTERVENTIONS: The patient was treated with a series of conservative treatments including antibiotic treatment, saline irrigation and laser irradiation, as well as superficial sequestration was. One year later, a mandibular osteotomy was performed. OUTCOMES: For the patient, the symptoms of gingival swelling, pain and discharge disappeared after surgery. LESSONS: These findings suggested MRONJ and MM could occur simultaneously at same site, so patients with MM presenting with symptoms of MRONJ should be screened for concurrent or disease relapse of multiple myeloma to prevent misdiagnosis or inadequate management. Meanwhile, this also suggests long-term inflammatory may lead to invasion of multiple myeloma.