Abstract:
Introduction. The Numb chin syndrome (NCS) also known as mental neuropathy is a rare sensory neuropathy
characterised by oral and lower face numbness, often in association with jaw pain and paresthesia. The hypoesthesia
usually involves the lower lip, chin and/or lower anterior teeth mucosa. The clinical acknowledgement of the NCS is
important mainly because frequently can be the first clinical manifestations of an occult malignancy. Breast cancer
and non-Hodgkin lymphoma are the most common reported causes of NCS. Hypoesthesia can occur unilaterally or
bilaterally. Thorough diagnostic evaluation should always be performed when no clear cause is evident.
Aim of study. The first report of mental neuropathy as the initial presentation of malignancies dates from 1963. The
mental nerve has no motor fibres that is why the NCS is a purely sensory neuropathy. The mandibular branch of the
trigeminal nerve leaves the skull through the foramen ovale dividing into two trunks: an anterior motor trunk for
mastication muscles and a posterior sensory trunk passing through the mandible and forming the inferior alveolar
nerve. The last exits the mental foramen as the mental nerve, responsible for the sensation of the lower lip and the
skin of the chin. In most cases, the neuropathy results from mechanical compression or tumour infiltration. The most
common haematologic neoplastic cause is non-Hodgkin lymphoma (NHL). The NCS is an under-recognised
condition in spite of the fact that NCS is vastly documented in the literature. Thus, the lack of awareness causes delay
in diagnosis and treatment.
Methods and materials. Desktop research with systematic review on Medline, PubMed, Mendeley, Google scholar
and Google searching for articles published in English until February 28, 2022 with the search terms “Hodgkin and
non-Hodgkin disease,” “lymphoma,” “neurolymphomatosis” in combination with “Numb Chin syndrome,” and
“mental neuropathy”.
Results. Usually, the NCS is the first sign of recurrence or metastasis in patients with a history of malignancy. Often
though, the NCS is the first manifestation in hematologic malignancies, preceding the diagnosis of the primary
tumour. The NCS can underline many malignant conditions, including lymphoma, acute leukaemia, Burkitt
lymphoma, multiple myeloma, Ewing sarcoma, melanoma, but also breast, lung, esophageal colon and prostate
cancers. The pathophysiology of NCS can vary from direct compression of the mental nerve by the tumour,
leptomeningeal invasion or lesion of the bone at the mental foramen. Heavy infiltration of tumour cells in the
trigeminal nerve and destruction of axons and myelin in the mandibular nerve have been reported in post-mortem
studies. A particular vulnerability of inferior alveolar nerve/mental nerve to malignant alteration is due to their
tortuous course through the mandibular bone. Is interesting though that the bilateral NCS are more often associated
with hematologic malignancies than with solid malignancies. This could be explained by the infiltrative character of
the hematologic malignancies versus the solid tumours.
Conclusion. The NCS may be a subtle sign of occult malignancy progression or recurrence or disease progression
in patients with a history of cancer; • Thus, the panoramic radiography of the jaw, computed tomography (CT) or
magnetic resonance image (MRI) of the jaw, face, and brain makes shall be compulsory for every NCS; • The most
common non-haematologic neoplastic cause of NCS is breast cancer, while the most common haematologic
neoplastic cause is NHL; • The exact pathophysiology of NCS is still unclear. Currently known mechanisms include
direct compression of the mental nerve by tumour mass, leptomeningeal invasion or a bony lesion at mental foramen.
However, other mechanisms may also exist, such as dural lesions.