Trigeminal neuralgia is the most common type of neuralgias. Incidence estimated to be one every 25000 adults. The condition occur without any apparant organic cause and it is characterized by classic diagnostic symptoms. (Table 2)
Table 2. Classical symptoms of trigeminal neuralgia.
- Paroxyamal attacks of pain which lasts for seconds or minutes.
- Provacation of the attack by gentel surface stimulation of the trigger zone.
- Pain is limited to the distribution of the branches of the trigeminal nerve.
- Unilateral occurance, pain never cross the midline.
- Lack of any sensory or motor nerve abnormalities.
The etilogy of trigeminal neuralgia is unknown and even the site of the primary lesion is uncertain. However, many possible etiological factors have been
suggested. These includes multiple sclerosis (a chronic disease of unknown etiology that result in damage of the myelin sheath of the nerves in the brain and the spinal cord), ischemia of the gasrian ganglion and dental etiological factors. The significance
of teeth as an etiological factor has been suggested based on some observations which are listed in table 2.
Signs And Symptoms
Trigeminal neuralgia is considered as a disease of senility as it usually affect patients in the 5th or 6th decade of life. Females are more commonly affected than males. For unknown cause the right side of the face is much more commonly affected than the
left side, while bilateral involvement is quite rare. The disease most commonly affect the mandibular or maxillary divisions of the trigmenal nerve more than the ophthalmic division.
Table 3. Clinical
observations which suggest a dental origin of the trigeminal neuralgia.
- The common occurance of the disease in the second and third divisions over the first division.
- The characteristic localization of the trigger zone in the oral or paraoral regions in most cases.
- The remission of the paroxysmal attacks of pain following the extraction
of teeth in some cases.
- The increased number of case reports which contributed the development of the disease to the presence of septic foci within the jaw bones.
Character of pain
Pain has an abrubt origin and the atacks lasts for seconds or few minutes.The attack could be initiated by slight afferent impulses to the trigger zones or may be evoked spontenously. Table 3 summurizes
the character of trigeminal neuralgia pain. Usually pain raadiates to the tretories of the nerve involved. However, pain may be refrred to an area innervated by other division.
Trigger zone mechanism
zone represents the primary site of origin of pain. In some cases the trigger zone is pinpoint in size while in other cases it is more diffuse. In some cases the triggr zone is so hy[erirritable that the displacement of a single haire is suffeicent to evoke
the attack. However, more commonly the attack is evoked by insignificant effort a chewing, drinking, yawing, talking, swallowing, touch or even an air draft. Mostly the trigger zone remains confined to a certain location but migration has been reported with
long standing cases. Charaterixtically the patient points to the trigger zone with his finger without touching it to avoid pricipitation of the attack. This is called “Half-an-inch sign”.
4. Charater of pain in trigeminal neuralgia.
- Abrupt onset.
- The attack lasts for seconds or few minutes.
- Pain is unberable, boring, burning, stabbing, sharp, shooting pain.
- Sometimes the attacks occur so rapidly that the patient complain of continous
pain. that lasts for several minutes or hours.
- The attack could be evoked by slight atterent impulses from the trigger zones or may be evoked spontinously.
- Between the attacks the patient is completely free from pain but there is some discomfort. This is usually due to headack and some paraesthesia, sorness and feeling of pressure over the trigger zone.
Treatment Of Trigeminal Neuralgia
This drug is used mainly for treatment of epilepsy. However the dose required to control the trigeminal pain is very near to the toxic level and can not be tolerated for an extended period of time.
- Vitamine B12: It offeres some relif
of pain but faile to achieve sustain relief of pain.
- Tegratol (Carbamazepine): This ia an anticonvulsant drug that is used to control the convulasion attaks in epilepsy. It is used also for relief of pain of trigeminal neuralgia.
The dose of the drug is increased gradually until the attacks no longer occur. The drug should be discontinued every three months and the patient is observed for any side effect. Side effects of tegratol include urtecaria and dermatitis, agranulocytosis, abnormalities
of liver and bone marrow, drowsiness, dizziness and muscular incoordination.
The idea of this line of treatment is to place the a chemical as alcohol, local anaesthetic agent
phenol or even boiling water in direct contact with the affected nerve. This will cause destruction of the nerve fibers and prevent the attacks of pain.
- Local Anaesthetic injection: Novacaine in oil emulsion is injected into the
trunk of the nerve affected. Injection is repeated 6-7 times. It has a neurolytic action and thus prevent the occurance of the attacks.
- Alcohol injection: Alcohol 95% is injected to cause interruption of afferent impulses to the higer
cortical center. This will produce prolonged anaesthesia. Alcohol may be injected peripherally near the trunk of the affected division or centrally into the gasserian ganglion. Table 10-4 shows some comments on the peripheral alcohol injection.
1. Peripheral Neurotomy
Pheripheral neurotomy, or post-ganglionic surgery, involves destruction or evulsion of the nerve at the mental, mandibular, infraorbital or
nasoplatine foramen. This procedure is rlatively easy to be performed and carry no mortalitiy or morbidity. However, pain recurrence is mandatory with the regeneration of the evulsed nerves. Peripheral neurectomy is superior to alcohol injection as nerve regeneration
takes longer time and no damage to the surrounding tissue occurs. The period of pain relief becomes longer with repeated neurectomies.
Lingual nerve neurectomy
- An incisionis made at the plica sublingualis
just medial to the retromolar triangle thus the nerve is exposed as it crosses over the wharton’s duct.
- The lingual nerve at this site is large enough to be easily identified, graspped and evulsed.
- A U-shaped incision is made in the canine fossa and a mucoperiosteal flap is reflected upward to expose the infraorbital foramen.
- The nerve is then identified as it emergs from the foramend
and grassped with a hemostate and evulsed. The entire trunk can be removed by winding it on the hemostate.
Inferior dental nerve neurectomy
- Incision is
made along the anterior boder of the ramus. The medial pterygoid muscle fibers are splitted and the nerve is located.
- Another incsion is made over the mental nerve which is exposed, grassped by a hemostate and evulsed.
inferior dental nerve is also divided at the mandibular foramen and then evalused out of the canal. This can be done by slowly rolling of the nerve on a hemoast.
incision is made and the lateral surface of the ramus is exposed.
- A window is then cut on the cortes and the spongiosa to expose the canal. The nerve is then lifted up by a nerve hook and divided between two hemostats.
nerve is then evulsed very slowly from the canal.
2. Retrogasserian Rhizotomy
Retrogasserian rhizotomy is a preganglionic surgry which is performed intracranial. The sensory roots of the gasserian ganglion are selectively
cut which result in permenant anaesthesia over the areas supplied by cut nerves.However, the procedure carry great risk of morbidity and mortality.
3. Nerve Decompression
This is an intracranial procedure in which an incision
is made in the dura that surrounds the gasserian ganglion and its sensory roots. Gentel freeing of the gasserian ganglion and its sensory root results, for unknown cause, in pain elimination with retention of tactile and proprioceptive sensations.