Numb chin syndrome.

CLINICAL HISTORY This 67-year-old man was seen in neurological consultation with a 10-day history of numbness and tingling of the right chin which was intermittent for the first 3 days and then constant for one week. The chin could also be intermittently painful with an intensity ranging from 7 to 9/10 especially with chewing. He had no headache, speech disturbance, dysphagia, visual disturbance, or other neurological symptoms. After seeing his primary care physician, he then saw both an ENT physician and oral surgeon without a cause being found. Mandible x-rays were negative. There was a past medical history of prostate carcinoma initially diagnosed on biopsy 4 years previously when he was started on leuprolide injections. He developed bony metastases requiring palliative radiotherapy to the hips and lower extremities completed about 6 weeks previously. His medications were ketoconazole and hyodrocortisone. Neurological examination was normal except for decreased sensation over the right chin and right lower lip. A magnetic resonance imaging (MRI) of the brain and skull base with and without contrast was normal. The Westergren erythrocyte sedimentation rate was 47 mm/hour. Questions.—What is the diagnosis? What are the possible etiologies? What testing is indicated when presented with similar symptoms?