Background/Purpose Numb chin syndrome (NCS) is a critical sign of systemic malignancy; however it remains largely unknown by clinicians and dentists. The aim of this study was to investigate NCS that is more often associated with metastatic cancers than with benign diseases. Methods Sixteen patients with NCS were diagnosed and treated. The oral and radiographic manifestations were assessed. Results Four (25%) of 16 patients with NCS were affected by nonmalignant diseases (19% by medication-related osteonecrosis of the jaw and 6% by osteopetrosis); yet 12 (75%) patient conditions were caused by malignant metastasis, either in the mandible (62%) or intracranial invasion (13%). NCS was unilateral in 13 cases and bilateral in three cases. Mandibular pain and masticatory weakness often dominate the clinical features in NCS associated with cancer metastasis. In two patients, NCS preceded the discovery of unknown malignancy (breast cancer and leukemia). In nine others, NCS heralded malignancy relapse and progression. Metastatic breast cancer in four (36%) cases accounted for the most common malignancy. Other metastatic diseases included two multiple myelomas, and one each of leukemia, prostate cancer, colon cancer, lung cancer, maxillary sinus adenoid cystic carcinoma and adrenal gland neuroblastoma. Radiographic examinations showed obvious mandibular metastasis with compression of the inferior alveolar nerve or mental nerve in nine patients, and leptomeningeal seeding or intracranial metastasis to the trigeminal nerve root at the skull base in two patients. Conclusion NCS without obvious odontogenic causes or trauma often signals systemic malignancy. It may be the first clue of occult malignancy.
