Trigeminal neuralgia

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Definition and Etiology

Neurovascular conflicts include a set of syndromes caused by the compression of the cranial nerves and generally corresponding to their entry point into the brainstem (root entry zone or REZ).

The REZ corresponds to the point in which the sheath (myelin) of central origin (oligodendrocytes) is modified into peripheral myelin (Schwann cells).

Trigeminal neuralgia or tic doloreux is one of the most frequent causes of facial pains and affects the areas that are innervated by the trigeminal nerve. The latter is the fifth pair of cranial nerves, which is in charge of the sensory perception of the face and exerts some motor functions (such as chewing).

The incidence of neuralgia is equal to 4-5 new cases per year for every 100,000 inhabitants and is higher in the female gender.

Being a prevalently sensitive nerve, the surface of the face is considered as its origin. From there the fibres converge through the three branches (hence the name trigeminal) ophthalmic (V1), maxillary (V2), and mandibular (V3) into the Gasserian ganglion to then end in their own nucleus within the brainstem.

The ophthalmic branch supplies sensations to the frontal region of the face and to the maxillary region of the nose and jaw, while the mandibular branch supplies sensations to the mouth and mandibular arch.

Trigeminal neuralgia in its typical form is characterised by four elements:

  • piercing or electrical pain generally in one or more of the three territories or divisions of the trigeminal nerve

  • presence of points on the face which, if stimulated, evoke the pain (trigger points) (middle of the eyebrow, nose wing, hemilip)

  • specific stimuli inducing the pain (triggers)

  • sudden beginning of the symptoms

Trigeminal neuralgia generally appears in subjects who are older than 50, and can induce extremely negative effects on the patient’s emotional structure, since he/she will experience periods of intense pain alternated by moments of fear for the possible return of the symptoms.

In the past, when there was no possible cure, some patients would even face suicide to end this atrocious pain.

In most patients, typical trigeminal neuralgia is caused by the close contact of the nerve with a cerebellar artery (neurovascular conflict), in a smaller number of cases the conflict can be with a vein.

The repeated contact with an artery (and its respective pulsatility) causes the trigeminal to lose the myelin sheath covering the sensory fibres, which tend to develop anomalous spontaneous impulses that reveal themselves with the well-known painful sensations.

Atypical trigeminal neuralgia is characterised by an absence of defined trigger points, intermittent or persistent pain, numbness of the face. In these cases, even a reduction of taste, in particular of salty foods, can be perceived.

The causes of atypical trigeminal neuralgia should be investigated in other concomitant pathologies, such as multiple sclerosis, Herpes infections, skull base tumor, with consequent direct compression of the nerve.

Multiple sclerosis is the cause of about 2% of trigeminal neuralgias. 18% of all patients with bilateral trigeminal neuralgia suffers from multiple sclerosis.