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
Commonly affected area in numb chin syndrome

Clinical Features[edit | edit source]

  • 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[edit | edit source]

Pathophysiology[edit | edit source]

  • 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[edit | edit source]

Dental and Traumatic Injury[edit | edit source]

  • 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[edit | edit source]

  • 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
    • Common primary sites:[1]
      1. Breast cancer (40%)
      2. Lymphoma (21%)
      3. Prostate cancer (7%)
      4. Leukemia (5%)

Infection[edit | edit source]

  • Syphilis
  • Lyme's disease
  • Herpes

Drugs[edit | edit source]

  • Mefloquine (malaria)
  • Allopurinol (gout)
  • Interferon-alpha (leukaemia, melanoma, lymphoma, Hep B and Hep C)

Inflammatory/Autoimmune[edit | edit source]

  • Numb chin syndrome can be a rare presentation for the following:
    • Multiple Sclerosis
    • Giant cell arteritis
    • Post-hepatitis B vaccination
    • Systemic Lupus Erythematosus
    • Sjögren syndrome
    • Scleroderma
    • Rheumatoid arthritis
    • Mixed connective tissue disease
    • Dermatomyositis
    • Sarcoidosis
    • Diabetic polyneuropathy (usually subclinical)

Sickle Cell Disease[edit | edit source]

  • Vaso-occlusive disease → pain and numbness of chin

Investigations[edit | edit source]

  • Rule out dental, traumatic or iatrogenic causes
  • Following investigations may be helpful in evaluating new onset cases without obvious causes

Imaging[edit | edit source]

  • Orthopantogram (OPG)
    • Investigate for dental or traumatic cause
    • Will also demonstrate obvious boney pathology and lytic lesions
  • Computed tomography (CT)
    • For further delineation of boney pathology/trauma
  • Magnetic resonance imaging (MRI)
    • MRI of the head and neck can demonstrate any pathology along the full length of trigeminal nerve
    • Can also demonstrate demyelinating disease
  • Positron emission tomography (PET)

Laboratory Investigations[edit | edit source]

  • Routine bloods
    • FBC, ESR, CRP
  • Bloods for specific diseases
    • Aninuclear antibodies, Antibodies to extractable nuclear antigens (Ro/SSA and La/SSB), HBA1C, ACE assay
  • Peripheral blood smear (lymphoma/leukaemia screen)
  • Infective screen
    • HIV
    • Lyme serology
    • Syphilis
    • Herpes simplex virus testing

Other[edit | edit source]

  • Cerebrospinal fluid analysis
    • Consider if no history of trauma and all above imaging is negative
    • May reveal presence of malignant cells

Management[edit | edit source]

  • Address the cause

Prognosis and Complications[edit | edit source]

  • Again cause dependent
  • Numb chin syndrome caused by malignancy has a poor prognosis - overall mortality around 80% with mean survival of 7 months[1]

References[edit | edit source]