Numb chin syndrome: An uncommon presentation of metastatic non-small cell lung cancer diagnosed by 18F-FDG PET/CT scan

Objective: To present an uncommon presentation of metastatic non-small cell lung cancer at mandible causing numb chin syndrome (NCS), diagnosed by PET/CT scan. Case presentation: A 72-year-old man presented with decreased sensation of left lower lip without motor deficit or taste alteration, so called NCS. Work up was initially focused on benign etiology as patient had no known malignancy. However, malignancy was suspected after excluding all possible benign causes. Further investigation showed high level of adenocarcinoma markers and a lytic lesion at sacrum leading to provisional diagnosis of bone metastasis with unknown primary cancer. The subsequent fluorine-18 fluorodeoxyglucose positron emission tomography/ computerized tomography (¹⁸F-FDG PET/CT scan) showed a pulmonary mass, representing primary lung cancer with multiple metastatic sites, including the destructive lesion at left mandible which was a cause of NCS. Conclusion: NCS could be an atypical presentation of malignancy. Among several investigations for NCS, PET/ CT scan may rarely be used. However, PET/CT scan may provide substantial benefits, particularly for metastatic disease with unknown primary cancer.