Numb Chin Syndrome

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  • Numbness/decreased sensation of the chin and lower lip
  • Easily underemphasised by clinicians and patients
  • Caused by a wide range of differentials - some associated with significant morbidity and mortality

Epidemiology

  • Epidemiology
  • ♀ > < = ♂

Clinical Features

  • Paraesthesia, dysaesthesia or anaesthesia to chin and lower lip (mental/inferior alveolar nerve region)
    • Malignancy tends to be associated with numbness (pain occurs in <10% of cases associated with malignancy)[1]
  • Patients with skull based metastasis can also present with other cranial nerve abnormalities
  • Patients with mandibular tumours may also present with swelling, loose teeth etc

Aetiology and Pathogenesis

Pathophysiology

  • Can occur from a lesion anywhere along the course of the trigeminal nerve (including as proximal as trigeminal ganglion and pons)
  • Lesions can be divided into:
    1. Peripheral lesions - involving mandible, direct nerve infiltration , inflammation or compression
    2. Central lesions - involving the base of skull, leptomeninges, or brainstem
  • Malignancy associated cases can occur through the following mechanisms:
    1. Direct infiltration of the nerve
      • Head and neck primary or metastasis from distant site to mandible
    2. Leptomeningeal seeding
      • May have no obvious mass in the mandible or skull base
      • These cases are thought to be due to leptomeningeal seeding[2][3][4]
    3. Cervical lymphadenopathy
      • Nodes in the deeper upper cervical region can exert pressure on the inferior alveolar nerve just before it enters the mandibular foramen[5]
    4. Paraneoplastic Phenomenon
      • Antibodies may be directed against unknown antigens in the nervous system[6]

Causes

Dental and Traumatic Injury

  • Most common cause
  • Dental (odontogenic cysts, abscesses, trauma)
  • Facial trauma
  • Iatrogenic injury (extraction of teeth, local anaesthetic blocks, endodontic treatment, orthographic surgery, dental implants, MRONJ)

Malignancy

  • Primary tumours
    • Squamous cell carcinoma
    • Melanoma (of lower lip)
    • Lymphoma
    • Myeloma
  • Metastasis
    • Mandible is the most common site for metastatic lesions to present in the oral and maxillofacial complex
    • 1-3 percent of oral and maxillofacial tumours are metastatic lesions[7]

Infection

Drugs

Inflammatory/Autoimmune

Sickle Cell Disease

Investigations

Laboratory Investigations

Imaging

Other

Management

  • Management

Prognosis and Complications

  • Prognosis and Complications

Follow-up

  • Follow-up

References

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