Abstract
We encountered a patient with acute lymphocytic leukemia initially presenting as numb chin syndrome, a condition in which monoplegia of the mental nerve causes numbness, hypesthesia, and loss of sensation from the lower lip to the chin. The patient was a 14-year-old boy with pain, numbness, and anesthesia from the right lip to the lower jaw. Pain, numbness, and anesthesia were confirmed to extend from the right lip to the third branch of the trigeminal nerve, and the right palatine tonsil was also swollen. The patient did not exhibit any hematological abnormalities such as anemia, cytopenia, or blast cells, and diagnostic imaging did not reveal any abnormalities other than a swollen right palatine tonsil. Based on the results of palatine tonsil biopsy and bone-marrow aspiration, mature B-cell leukemia was diagnosed. Malignant tumor is frequently identified as the underlying cause of numb chin syndrome, which tends to be regarded lightly due to the mild nature of the symptoms. However, numb chin syndrome is clinically significant as a frequent initial symptom of malignancy. For this reason, even in the absence of symptoms suggesting acute lymphocytic leukemia such as our case, malignant tumor should be suspected in patients presenting with numbness from the lip to the lower jaw, and the underlying cause of the numbness should be investigated.
