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Symptoms of Trigeminal Neuralgia – Cause of Pain – Diagnostic Work up In Trigeminal Neuralgia – Prognosis
Symptoms of Trigeminal Neuralgia
Trigeminal neuralgia is a strong shooting, toothache-like, debilitating pain typically limited to one side of the face. Most commonly, the pain involves mid-to-upper part of the face and spreads lower during exacerbations. The epicenter of the pain varies from patient to patient. Very often it is pointed to some area near the nose, cheek or near the orbit. Isolated involvement of the lower third of the face is not typical for trigeminal neuralgia.
If you’ve ever experienced a toothache, it is not hard to imagine the type of pain caused by trigeminal neuralgia. It is felt as a “toothache” in the face. Pain in trigeminal neuralgia is almost constant, exhausting and very uncomfortable with episodic exacerbations and transformation into shooting, electrical, burning pain.
Trigeminal nerve supplies tissues inside the mouth (teeth, gums) as well as the skin on the outside. Pain, which is limited to inside the mouth or to the surface of the face alone, is unlikely caused by trigeminal neuralgia.
The face and the mouth become very sensitive to the touch and temperature change. A simple touch, cold wind blow, or a water splash to the painful side of the face brings up bouts of shooting pain. Simple things like tooth brushing, eating or talking become problematic due to exacerbation of the pain. Quality of life suffers dramatically.
Worst of all, conventional pain medications, including narcotics, have no effect on the pain caused by trigeminal neuralgia.
Natural course and severity of trigeminal neuralgia is variable. More likely than not, the pain will be chronic with episodic improvements and exacerbations. In some patient it may remit for some time. A complete and permanent spontaneous resolution of the pain in trigeminal neuralgia is uncommon and rather points to alternative diagnosis.
Normal Pain Processing Mechanism
Pain is an essential protective sense, which limits the extent of body damage. “Normal” pain is any pain produced by natural mechanisms, or by some tissue injury. Whether you hit your knee, or you have a tooth cavity, in both cases, tissue damage irritates the pain sensitive nerve endings. Pain is an alarm or a warning sign.
Pain processing system is organized in a manner similar to a typical alarm system. A sound of broken glass (tissue damage) turns on a special sensor (pain receptors, or nerve endings). Wires (trigeminal nerve fibers) carry the data to the relay station inside the house, which performs some initial processing. In this case it is the nucleus of trigeminal nerve located in the brainstem. This nucleus contains thousands of interconnected nerve cells (neurons) which sort out the data and do some work on initial localization and injury type processing. At this level we are not conscious about the injury.
The relay station sends the information about the type of damage and the intruder’s entry zone to the central station, where the decision about further actions is made. In trigeminal system, the nucleus sends all the information about the location and the type of sensation (hot, cold, pain, pressure) to the higher processing centers.
The top level processing centers make decisions about the type of injury (sharp, cut, dull object, burn, frost bite) and present it to the consciousness, so that the mind becomes aware of the problem.
Let’s see now, what happens in trigeminal neuralgia with the pain processing.
Cause of Pain in Trigeminal Neuralgia
In trigeminal neuralgia, the pain is produced by the “relay station” or by the nerve cells in the nucleus of the trigeminal nerve. There is no tissue damage. The perceived pain is a mere “false alarm” erroneously sent for processing. When the pain reaches consciousness, its location and quality is hard to interpret. It is a mix of randomly generated signals. This is why it is so hard to describe the quality and the location of this pain. This statement holds true in any type of neuropathic pain.
What is the cause of this false alarm? The cause is some factor that produces a prolonged “irritation” of the nerve trunk. Some of the cases are caused by a vascular loop pressing on the trigeminal nerve root entry zone. Considering that arteries are constantly pulsating, these repetitive waves of pressure irritate the nerve and eventually overexcite the nerve cells in the nucleus. Another possibility is a compression of one of the nerve branches inside a skull bony canal.
Herpes zoster may cause neuralgic pain in the face but this pain does not have classical features of trigeminal neuralgia and is typically self-limited.
In Multiple Sclerosis , an inflammation in the brainstem tissue is a causative factor of the “nerve irritation” and trigeminal neuralgia-like clinical picture.
Chronic repetitive stimulation of the trigeminal nerve root entry zone makes neurons in the trigeminal nerve ganglion hyperexcitable. Those neurons are heavily interconnected and they stimulate each other. Eventually the network catches a “fire”, which brings up this pain syndrome. The excitation wave spreads throughout the nucleus, which translates into a wave of the shooting pain that may engulf a substantial portion of the face. Any natural stimulation of the pain and temperature receptors or even touch receptors adds an extra fuel in the fire. This is why the face becomes so sensitive and any normal sensation triggers a shooting pain attack.
The processes described above are very similar to the ones that occur in the brain cortex in epilepsy. This is probably why the most effective drugs in trigeminal neuralgia are antiepileptic drugs.
Diagnostic Testing in Trigeminal Neuralgia
Trigeminal neuralgia is a clinical diagnosis. The diagnosis is based exclusively on the symptoms and the results on neurological examination. There are no diagnostic tools to confirm or to rule out the diagnosis of trigeminal neuralgia.
Vascular loop compressing the trigeminal nerve root entry zone can be seen on a high resolution MRI of the posterior cranial fossa.
Loss of sensation is uncommon in trigeminal neuralgia. Diagnostic tests are also useful in determination of the cause of trigeminal neuralgia- like pain, when the symptoms are not very typical. Tumors, infections (herpes, Lyme disease) or some other inflammatory diseases (sarcoidosis) have to be considered. Brain MRI with a contrast is usually sufficient to address these concerns.
Trigeminal neuralgia in a young person and especially bilateral may be a symptom of Multiple Sclerosis. A contrast enhanced Brain MRI is recommended as well.
Trigeminal neuralgia is called primary if no damaging factor is identified and there is no evidence of trigeminal nerve injury. Otherwise, it is called secondary. It is hard to confirm trigeminal nerve damage when neurological examination is normal. There is only one electrophysiological test, Blink Reflex, which can instrumentally confirm trigeminal nerve conduction abnormality.
Primary trigeminal neuralgia responds to conservative treatment better than secondary.
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