Primary (idiopathic) trigeminal neuralgia is defined as a condition in which no neurological signs are found clinically and no organic or functional lesions related to the onset of the disease are detected on relevant investigations. The pathogenesis may be an injury-causing factor that causes changes in the sensory roots, the semilunar ganglion and the adjacent motor branches to become desynchronized. It has been clinically proven that some of the so-called primary trigeminal neuralgia can actually still find an etiology, such as sclerosis of the blood vessels supplying the nerve, compression by ectopic vessels, and the nerve passing through a narrow bone hole caused by osteochondritis, which can cause compression of the nerve root.
I. The etiology of primary trigeminal neuralgia has the following theories.
(1) Local stimulation theory
Inflammatory lesions occur in the tissues and organs innervated by the trigeminal nerve, such as paranasal sinusitis, odontogenic inflammation, or traumatic lesions, forming long-term chronic irritation, which can cause inflammation and fibrosis of the nerve and poisoning of the semilunar ganglion, further causing dysfunction and spasm of the trophoblastic vessels distributed on the trigeminal nerve root, and finally secondary ischemia, resulting in demyelinating lesions of the sensory root, and causing trigeminal neuralgia.
( 2 ) Compression theory
Trigeminal neuralgia is caused by compression or pulling on one of the sensory roots of the trigeminal nervous system for various reasons.
① Vascular compression theory.
Mechanical compression of the trigeminal nerve, i.e., compression of the trigeminal nerve root by the basilar and superior cerebellar arteries, is an important cause of pain and is the most common cause, so vascular decompression surgery is often used to treat the disease.
(2) Bone compression theory:
This type of compression can be divided into two categories: congenital and acquired. The main cause of compression is trigeminal neuralgia due to elevation of the lamina cribrosa, narrowing of the foramina and supratentorial sinus variation. The elevation of the rock bone angle is mostly congenital, usually more on the right side than on the left. Bone foramen stenosis is also mostly congenital, while acquired causes of bone foramen stenosis are mostly due to skull injury skull base fractures. The extent of their trigeminal nerve pain is consistent with the narrowed bone foramen, such as oval foramen stenosis, where the pain occurs within the mandibular distribution area. Osteophytes and hyperplasia caused by inflammation of the periosteum can narrow the foramen. This condition is mostly acquired and mostly in elderly patients.
( 3 ) The doctrine of dentition system disorder can cause trigeminal neuralgia. As early as in the 1930s, dentists found in clinical practice that trigeminal neuralgia is more likely to occur in the maxillary and mandibular branches, and such patients are often accompanied by disorders of the dentition system. These patients often have a disorder of the dental system, such as early cusp contact, severe locking, deep overlap, absence of most posterior teeth, and low vertical distance due to excessive wear of the sympathetic surfaces. These disorders of the dentition can cause spasm and muscle dysfunction in the periarticular musculature. This condition forms a small amount of abnormal impulses and constantly transmits them to the center, which causes the center to lose its dynamic balance and dysfunction.
( 4 ) Ischemia theory
It was noted in the late 1940s that vasodilators had been used to treat patients with trigeminal neuralgia with some efficacy. It indicates that after vasodilation, trigeminal nerve root ischemia can be partially relieved, removing the ischemic stimulation of the trigeminal nerve and terminating the onset of pain. Later, some people found that the incidence of trigeminal neuralgia is high in patients with hypertension and atherosclerosis, and the incidence of trigeminal neuralgia is proportional to age because the older the patient is, the more likely he/she is to suffer from hypertension and atherosclerosis. Most scholars in recent years have concluded that ischemia cannot be a cause alone, but can be a cofactor. Ischemia of the trigeminal nervous system causes local malnutrition of this system, which reduces the nerve vitality and local resistance; then under the action of other factors, the trigeminal nerve can develop pain.
( 5 ) Central etiology theory
Trigeminal neuralgia is caused by dysfunction and organic lesions in the central part of the trigeminal nervous system, including the nucleus accumbens, thalamus and brain. It has been found that herpes and herpes simplex virus infection can invade the cranium along any pathway of the trigeminal nervous system (mainly through the olfactory nerve and trigeminal nerve) and latent in the trigeminal ganglion and spinal ganglion, which can cause trigeminal neuralgia attacks when invading the cerebral cortex innervating the trigeminal nerve.
( 6 ) The theory of metaplasia
It is believed that primary trigeminal neuralgia is caused by neurophysiological and chemical dysfunction. The principle of this allergic reaction is still unclear. It may be due to the abnormal protein digestion in allergic patients due to the lack of gastric acid, and the absorption of histamine-like substances into the blood, which reaches the trigeminal nerve root and the semilunar ganglion with the blood circulation, causing edema of the tissue in this area, which compresses and stimulates the trigeminal nerve and causes pain attacks.
( 7 ) Family genetic theory
It has been reported that several people in a family suffer from trigeminal neuralgia, so it is thought that this disorder may be related to family inheritance.
II. Clinical manifestations.
1. From the age of onset, trigeminal neuralgia occurs in young to old people, but the incidence is highest in people over 40 years old. There seems to be no difference in gender. There are slightly more women than men, with a ratio of 3:2.
2. The attack of the disease is characterized by a sudden onset of severe pain in the trigeminal nerve distribution area, such as cutting, burning, pinching or electric burning. Each attack lasts for tens of seconds to about 1-2 minutes, and in severe cases, the attacks can be repeated within a few minutes, or in mild cases, 1-2 attacks a day or one attack in several days.
3, in order to alleviate pain during the attack, patients often press the palm of the affected side of the face, for a long time can cause the side of the facial skin rough, eyebrows fall off, some patients in the attack to cover the face with their hands, while constantly chewing action, in order to alleviate pain. This painful face is unforgettable at first sight.
4. In the interval period, trigger points can often be found in the trigeminal nerve distribution area, also known as the starting point or boarder point. Such as the affected side of the eyebrow, nose, upper and lower lips, corner of the mouth, incisors, canines or cheeks, etc., a slight touch can trigger severe pain. In some cases, the pain can be triggered when speaking, brushing teeth, washing face, yawning, eating or drinking, resulting in patients not daring to speak, wash face or brush teeth, and only slowly feeding food from the corner of the healthy side of the mouth and chewing slowly, which seriously affects normal life and work.
5. No positive signs. There are no positive signs in the systematic neurological examination.
III. Diagnostic criteria.
1.Sudden onset of facial or frontal pain with a duration of several seconds to 2 minutes each time.
2. The pain has at least 4 of the following characteristics: the pain is fixed within the distribution area of one or more branches of the trigeminal nerve; the nature of the pain is sudden, intense, sharp, superficial stabbing pain, or burning pain; the intensity of the pain is extremely painful; the sudden pain starts in the trigger area or is triggered by some kind of evoked activity, such as eating, talking, washing the face, brushing the teeth, etc.; there is no pain between attacks.
IV. Treatment.
1. the preferred treatment for primary trigeminal neuralgia is pharmacotherapy. penfield et al. considered it to be a peripheral epileptiform discharge. Carbamazepine, bentoin sodium and clonidine are available. Early, mild trigeminal neuralgia can be effectively relieved by medication. However, patients with long-term, severe pain are difficult to obtain effective control by drugs, and the side effects of drugs are large and need to be taken for a long time.
2.Closure treatment. Injecting anhydrous alcohol or other chemical drugs directly into the trigeminal nerve branches or semilunar ganglion to cause coagulative necrosis, so as to block the nerve conduction function to pain and obtain pain relief. This method has rapid effect, but it is easy to recur.
3.Gamma knife treatment. Gamma radiation is focused on the root of the trigeminal nerve for a certain period of time and at a certain dose, causing nerve degeneration and necrosis, blocking conduction and pain relief. This method does not have any pain, the risk is small, but the medical cost is expensive. In addition, the early effect is inaccurate, and it is often effective only after half a year.
4.Surgical treatment. Microvascular decompression is to separate the cerebral vessels compressing the trigeminal nerve from the trigeminal nerve through craniotomy, and use various materials to isolate the vessels and nerve, so as to relieve trigeminal neuralgia.
5.Radiofrequency thermal coagulation technology treatment. Advanced foreign thermoregulation radiofrequency instruments are invoked, and the puncture is performed under CT or DSA monitoring, and the needle tip does not damage other nerves, which ensures the safety of the patient. Under shallow intravenous anesthesia, the needle tip reaches the lesion directly and acts on the root of the trigeminal nerve, so that the lesion nerve no longer transmits pain. Patients feel no pain during the whole treatment and only very light or no numbness of the skin and mucosa at all after the treatment, and the pain disappears.