Numb chin syndrome

Numb chin syndrome describes a sensory neuropathy occurring in the distribution of either the mental nerve or inferior alveolar nerve. While numb chin syndrome has a multitude of causes, it is considered an ominous entity due to its strong association with heralding advanced malignancy ¹.

Clinical presentation

Numb chin syndrome presents subtly with abnormal sensation to the chin and lower lip ^1-3. The abnormal sensation is usually numbness, but may be associated with paresthesia or localized pain ^1-3. The syndrome is usually unilateral, but can be bilateral in 10-15% of cases ^2,3.

Pathology

Numb chin syndrome is caused by a lesion of the trigeminal nerve, occurring anywhere from the central pathways to the mental nerve terminal branch. There are protean etiologies for numb chin syndrome, which can broadly be categorized into malignant and non-malignant causes. Overall, the most common causes are local non-malignant odontogenic pathology and occult malignancy ⁴.

In malignancy-associated numb chin syndrome, the condition can be the first sign of malignancy in approximately 30% of cases ³. This can occur due to a number of postulated mechanisms, including mechanical compression along the course of the trigeminal nerve (e.g. at the skull base or mandible) or through perineural infiltration ^1-3.

Etiology

• non-malignant ^1-3

  • odontogenic: e.g. infection, medication-related osteonecrosis of the jaw, dental local anesthetic, etc.

  • local trauma: e.g. inferior alveolar nerve injury, post-genioplasty, etc.

  • vasculitis, autoimmune and connective tissue diseases: e.g. giant cell arteritis, sarcoidosis, etc.

  • sickle cell disease

  • systemic infection: e.g. HIV, Lyme disease, syphilis, etc.

  • radiotherapy

  • multiple sclerosis

  • ischemic stroke

  • diabetes mellitus

• malignant ^1-3

  • primary oropharyngeal or odontogenic malignancy

  • metastases: e.g. skull base, mandibular, leptomeningeal, etc.

    • numerous primary malignancies can be implicated, but the most common are breast cancer and lymphoma

Radiographic features

Radiographic features depend on the underlying cause. A thorough work-up may include the following imaging modalities, with the intent to exclude a malignant etiology ^2,4,5:

• orthopantomogram (OPG)

• CT brain, skull base and facial bones

  • especially if there is a history of trauma

• MRI, contrast-enhanced with dedicated views of the brain, brainstem, skull base, and mandible

  • especially if there is no history of trauma

Treatment and prognosis

Management is highly variable and depends upon the underlying cause. In malignancy-associated numb chin syndrome, presence of this syndrome is associated with a poor prognosis ³.

History and etymology

The first description of numb chin syndrome was made by Sir Charles Bell (1774-1842), Scottish neurologist, in 1830 ⁶.