Mental neuropathy: report of five cases and review of the literature.

Mental nerve neuropathy, also referred to as numb chin syndrome, is a rare, seemingly harmless symptom. It is more often associated with cancer, either as first symptom or during the outcome, than with benign diseases. In this review, we will focus on the numb chin syndrome presenting as an isolated neurological symptom. We report five patients with mental nerve neuropathy associated with metastatic disease (small cell lung cancer, prostatic cancer and breast cancer). In one patient, numb chin syndrome preceded the discovery of the disease, while, in the four others, it occurred as a sign of relapse or progression. Isolated mental nerve neuropathy, frequently associated with breast cancer and lymphoproliferative diseases, is generally thought to be the consequence of bone metastases or leptomeningeal seeding, but may also present without an obvious cause, most often secondary to the involvement of the mental nerve itself. Although various therapies may lead to the resolution of this symptom, median survival after diagnosis is generally less than 1 year. The appearance of a mental nerve neuropathy should never be considered as a 'banal' symptom and investigations to detect a possible cancer should be mandatory.