Trigeminal neuralgia
Trigeminal neuralgia (TN or TGN), also called Fothergill disease, tic douloureux, trifacial neuralgia, or suicide disease, is a long-term pain disorder that affects the trigeminal nerve,[7][1] the nerve responsible for sensation in the face and motor functions such as biting and chewing. It is a form of neuropathic pain.[8] There are two main types: typical and atypical trigeminal neuralgia.[1] The typical form results in episodes of severe, sudden, shock-like pain in one side of the face that lasts for seconds to a few minutes.[1] Groups of these episodes can occur over a few hours.[1] The atypical form results in a constant burning pain that is less severe.[1] Episodes may be triggered by any touch to the face.[1] Both forms may occur in the same person.[1] It is regarded as one of the most painful disorders known to medicine, and often results in depression and suicide.[5]
The exact cause is unknown, but believed to involve loss of the myelin of the trigeminal nerve.[1][6] This might occur due to compression from a blood vessel as the nerve exits the brain stem, multiple sclerosis, stroke, or trauma.[1] Less common causes include a tumor or arteriovenous malformation.[1] It is a type of nerve pain.[1] Diagnosis is typically based on the symptoms, after ruling out other possible causes such as postherpetic neuralgia.[8][1]
Treatment includes medication or surgery.[1] The anticonvulsant carbamazepine or oxcarbazepine is usually the initial treatment, and is effective in about 90% of people.[8] Side effects are frequently experienced that necessitate drug withdrawal in as many as 23% of patients.[8] Other options include lamotrigine, baclofen, gabapentin, amitriptyline and pimozide.[6][1] Opioids are not usually effective in the typical form.[1] In those who do not improve or become resistant to other measures, a number of types of surgery may be tried.[6]
It is estimated that trigeminal neuralgia affects around 0.03% to 0.3% of people around the world with a female over-representation around a 3:1 ratio between women and men.[9] It usually begins in people over 50 years old, but can occur at any age.[1] The condition was first described in detail in 1773 by John Fothergill.[10]
Causes[edit]
The trigeminal nerve is a mixed cranial nerve responsible for sensory data such as tactition (pressure), thermoception (temperature), and nociception (pain) originating from the face above the jawline; it is also responsible for the motor function of the muscles of mastication, the muscles involved in chewing but not facial expression.[20]
Several theories exist to explain the possible causes of this pain syndrome. It was once believed that the nerve was compressed in the opening from the inside to the outside of the skull; but leading research indicates that it is an enlarged or lengthened blood vessel – most commonly the superior cerebellar artery – compressing or throbbing against the microvasculature of the trigeminal nerve near its connection with the pons.[21] Such a compression can injure the nerve's protective myelin sheath and cause erratic and hyperactive functioning of the nerve. This can lead to pain attacks at the slightest stimulation of any area served by the nerve as well as hinder the nerve's ability to shut off the pain signals after the stimulation ends. This type of injury may rarely be caused by an aneurysm (an outpouching of a blood vessel); by an AVM (arteriovenous malformation);[22] by a tumor; such as an arachnoid cyst or meningioma in the cerebellopontine angle;[23] or by a traumatic event, such as a car accident.[24]
Short-term peripheral compression is often painless.[5] Persistent compression results in local demyelination with no loss of axon potential continuity. Chronic nerve entrapment results in demyelination primarily, with progressive axonal degeneration subsequently.[5] It is, "therefore widely accepted that trigeminal neuralgia is associated with demyelination of axons in the Gasserian ganglion, the dorsal root, or both."[25] It has been suggested that this compression may be related to an aberrant branch of the superior cerebellar artery that lies on the trigeminal nerve.[25] Further causes, besides an aneurysm, multiple sclerosis or cerebellopontine angle tumor, include: a posterior fossa tumor, any other expanding lesion or even brainstem diseases from strokes.[25]
Trigeminal neuralgia is found in 3–4% of people with multiple sclerosis, according to data from seven studies.[26][27] It has been theorized that this is due to damage to the spinal trigeminal complex.[28] Trigeminal pain has a similar presentation in patients with and without MS.[29]
Postherpetic neuralgia, which occurs after shingles, may cause similar symptoms if the trigeminal nerve is damaged, called Ramsay Hunt syndrome type 2.
When there is no apparent structural cause, the syndrome is called idiopathic.
Diagnosis[edit]
Trigeminal neuralgia is diagnosed via the result of neurological and physical tests, as well as the individual's medical history.[1] Magnetic resonance angiography can be used to detect vascular compression of the trigeminal nerve and refer patients to surgery.[30]
As with many conditions without clear physical or laboratory diagnosis, TN is often misdiagnosed, and other conditions are also frequently misdiagnosed as TN.[31][32] A person with TN may see three or four clinicians before a firm diagnosis is made.[31]
Temporomandibular disorder (TMD) can present similarly to TN, and differentiating between these conditions can be difficult.[33] Even suspected TN patients who experience brief attacks of sharp pain have had their symptoms resolve after being treated for TMD.[34] TMD pain can also be triggered by movements of the tongue or facial muscles, so TN must be differentiated from masticatory pain by differentiating between the clinical characteristics of deep somatic pain and neuropathic pain. Masticatory pain will not be arrested by a conventional mandibular local anesthetic block.[14] One quick test a dentist might perform is a conventional inferior dental local anesthetic block. If the pain is in the treated branch, the block will not arrest masticatory pain but will alleviate TN pain.[35]
Some individuals of note with TN include: