We define seven forms of TN: typical TN, atypical TN, pre-TN, multiple-sclerosis-related TN, secondary TN, post-traumatic TN (trigeminal neuropathy), and failed TN. These forms of TN should be distinguished from idiopathic (atypical) facial pain, as well as other disorders causing cranio-facial pain.
Typical Trigeminal Neuralgia (Tic Douloureux)
This is the most common form of TN, that has previously been termed Classical, Idiopathic and Essential TN. Nearly all cases of typical TN are caused by blood vessels compressing the trigeminal nerve root as it enters the brain stem. This neurovascular or microvascular compression at the trigeminal nerve root entry zone may be caused by arteries of veins, large or small, that may simply contact or indent the trigeminal nerve. In people without TN, blood vessels are usually not in contact with the trigeminal nerve root entry zone.
|In people without TN, there is usually no vascular compression upon the trigeminal nerve root.||
|In most sufferers of typical trigeminal neuralgia, vessels compress the trigeminal nerve root.|
Pulsation of vessels upon the trigeminal nerve root do not visibly damage the nerve. However, irritation from repeated pulsations may lead to changes of nerve function, and delivery of abnormal signals to the trigeminal nerve nucleus. Over time, this is thought to cause hyperactivity of the trigeminal nerve nucleus, resulting in the generation of TN pain.
|The generation of TN pain is thought to result from peripheral pathology (i.e. neurovascular compression) and central pathophysiology (i.e. hyperactivity of the trigeminal nerve nucleus).|
The superior cerebellar artery is the vessel most often responsible for neurovascular compression upon the trigeminal nerve root, although other arteries or veins may be the culprit vessels. TN may be cured by an operation that effectively relieves the neurovascular compression upon the trigeminal nerve root. This operation is called microvascular decompression, and is described in Part Two: Treatment of Trigeminal Neuralgia.
C. Atypical Trigeminal Neuralgia
Atypical TN is characterized by a unilateral, prominent constant and severe aching, boring or burning pain superimposed upon otherwise typical TN symptoms. This should be differentiated from cases of typical TN that develop a minor aching or burning pain within the affected distribution of the trigeminal nerve.
Vascular compression, as described above in typical TN, is thought to be the cause of many cases of atypical TN. Some believe atypical TN is due to vascular compression upon a specific part of the trigeminal nerve (the portio minor), while others theorize that atypical TN represents a more severe form or progression of typical TN.
Atypical TN pain can be at least partially relieved with medications used for typical TN, such as carbamazepine (TegretolŪ). MVD surgery is curative for many patients with atypical TN, but not as reliably as for those with typical TN. It is also important to note that rhizotomy procedures may be effective in treating atypical TN, but are more likely to be complicated by annoying or even painful numbness (i.e. deafferentation pain).
D. Pre-Trigeminal Neuralgia
Days to years before the first attack of TN pain, some sufferers experience odd sensations in the trigeminal distributions destined to become affected by TN. These odd sensations of pain, (such as a toothache) or discomfort (like "pins and needles", parasthesia), may be symptoms of pre-trigeminal neuralgia. Pre-TN is most effectively treated with medical therapy used for typical TN. When the first attack of true TN occurs, it is very distinct from pre-TN symptoms.
E. Multiple Sclerosis-Related Trigeminal Neuralgia
The symptoms and characteristics of multiple sclerosis (MS)-related TN are identical to those for typical TN. Two to four percent of patients with TN have evidence of multiple sclerosis and about 1% of patients suffering from multiple sclerosis develop TN. Those with MS-related TN tend to be younger when they experience their first attack of pain, and the pain progresses over a shorter amount of time than in those with typical TN. Furthermore, bilateral TN is more commonly seen in people with multiple sclerosis.
MS involves the formation of demyelinating plaques within the brain. When these areas of injury involve the trigeminal nerve system, TN may develop. MS-related TN is treated with the same medications used for typical TN (see Medications). Trigeminal rhizotomies are employed when medications fail to control the pain. For some individuals with MS and TN, neurovascular compression of the trigeminal nerve root may be a rare cause and demonstrated with special MRI or CT scans. In such cases, microvascular decompression surgery may be considered for treating the MS-related TN.
F. Secondary or Tumor Related Trigeminal Neuralgia
neuralgia pain caused by a lesion, such as a tumor, is referred to as secondary
trigeminal neuralgia. A tumor that severely compresses or distorts the trigeminal
nerve may cause facial numbness, weakness of chewing muscles, and/or constant
aching pain (also see Trigeminal Neuropathy
or Post-Traumatic Trigeminal Neuralgia). Medications
usually help control secondary TN pain when first tried, although often become.
Surgically removing the tumor usually alleviates pain and trigeminal function
may return. At the time of surgery, after the removal of the tumor, the trigeminal
nerve may be found to also be compressed by an artery or vein that causes the
typical features of TN. This vessel must then be moved away from the nerve by
microvascular decompression techniques to cure TN.
In these MRI images, a tumor responsible for compressing the trigeminal nerve is highlighted in red.
G. Trigeminal Neuropathy or Post-Traumatic Trigeminal Neuralgia
Injury to the trigeminal nerve may cause this severe pain condition. Trigeminal Neuropathy or Post-Traumatic TN may develop following cranio-facial trauma (such as from a car accident), dental trauma, sinus trauma (such as following Caldwell Luc procedures) but most commonly following destructive procedures (rhizotomies) used for treatment of TN. Following TN injury, numbness may become associated with bothersome sensations or pain, sometimes called phantom pain or deafferentation pain. These pain conditions are caused by irreparable damage to the trigeminal nerve and secondary hyperactivity of the trigeminal nerve nucleus.
The pain of trigeminal neuropathy or post-traumatic TN is usually constant, aching or burning, but may be worsened by exposure to triggers such as wind and cold. Such deafferentation pain can start immediately or days to years following injury to the trigeminal nerve. In the most extreme form, called anesthesia dolorosa, there is continuous severe pain in areas of complete numbness.
Unfortunately, treatment of post-traumatic TN is often ineffective and pain may not be controlled with medications. There are some reports of pain relief associated with the use of trigeminal nerve stimulation procedures. More invasive procedures such as brain surface (pre-motor cortex) stimulation, or focused injuries in the brain stem (tractotomy) have also been tried.
H. "Failed" Trigeminal Neuralgia
Not all cases of TN may be effectively controlled with any one form of medications or surgical interventions. When medications are no longer effective, surgical interventions are considered. If pain recurs or persists following surgery, medications are tried again and may then work more effectively. Rarely, additional or repeated surgical interventions are necessary. Unfortunately, in a very small proportion of sufferers, all medications, microvascular decompression and destructive rhizotomy procedures prove ineffective in controlling TN pain. This condition is called "failed" trigeminal neuralgia. Such individuals also often suffer from additional trigeminal neuropathy or post-traumatic TN as a result of the destructive interventions they underwent. Investigational treatments may be considered including stimulation of the brain surface (pre-motor cortex stimulation), controlled lesioning of the brain stem (tractotomy), or stimulation of the trigeminal nerve or Gasserion ganglion (trigeminal nerve stimulation).
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