Diseases and Disorders

Tic Douloureux: An Overview

Aviral Batra


Abstract

Tic douloureux, or as it is more commonly known, trigeminal neuralgia (TN), is a chronic pain condition that affects the face resulting from a problem with the fifth cranial nerve, or the trigeminal nerve. It is characterised by sharp stabbing pains that can occur several times throughout the day. The name ‘tic douloureux’ or ‘painful tic’ comes from the facial expressions that patients make when wincing from the pain. The collateral effects of pain have led TN to gain names such as the ‘suicide disease.’ There are various options for treatment including pain medications and different surgeries to fix what is irritating the nerve or to damage the fibres that are transmitting pain. New drugs are also being designed to target the specific fibres causing pain.
 

A Very Brief History

The name Trigeminal Neuralgia is divided into two parts - ‘trigeminal,’ which indicates the nerve being affected, and ‘neuralgia’ which means a severe pain caused by the irritation of a nerve. Although this name is widely accepted today, the disease was once ‘tic douloureux,’ coined by the french doctor Nicolas André. ‘Tic douloureux’ in french or ‘painful tic’ is a reference to the wincing or facial tics that patients display as a result of the severity of the pain. Though the tics are not present in all patients, the name is still used [2].  Other names include prosopalgia (neuralgia affecting the face)  and Fothergill's disease, the latter signifying the first full account of the disease given by John Fothergill in 1773 [2]. However, descriptions of the symptoms can be inferred from the writings of Galen, the famous ancient physician born around 81 AD and of Avicenna, a significant Persian physician and polymath during the 11th century [2]. 

 

An Introduction to the Trigeminal Nerve

The trigeminal nerve is the fifth cranial nerve and it originates from a section of the brainstem known as the pons. It has 3 divisions: the ophthalmic division, giving sensation to the upper third of the face, the maxillary division, which provides sensation for the middle third of the face, and the mandibular division, which relays sensory information from the lower third of the face to the brain. The mandibular division also innervates the muscles required for mastication (chewing) [3]. It is usually the maxillary division that is involved in TN, however, the mandibular and ophthalmic divisions can be implicated as well.  disturbances in the sensory divisions of these nerves cause the symptoms of intense pain in TN [4]. 

 

Pathology and Causes

There are two ways in which TN can manifest itself: classic and symptomatic. The classic form is usually idiopathic (it arises spontaneously) and no cause can be identified other than a normal blood vessel compressing or coming into contact with the trigeminal nerve [6]. Symptomatic forms are caused by another underlying cause that irritates the nerve. This could range from tumours to aneurysms (enlarged portions of arteries due to wall weakness) that could compress the nerve [6].

Another less prevalent way in which TN can occur is if a person has multiple sclerosis (MS). Oligodendrocytes are cells in the central nervous system (CNS) - primarily consisting of the brain and spinal cord - that form myelin sheaths that wrap around neurons. Myelin sheaths are fatty and act as insulating deposits on neurons that speed up the transmission of nerve impulses necessary to maintain neurological function in areas of the CNS. In MS, immune cells from the blood can enter the CNS  and cause inflammation, attacking the myelin of these oligodendrocytes, leading to lesions (areas of damaged tissue). When the damaged myelin is replaced by scar tissue, this is called a plaque, which is harder than the myelin that was present before. This is why the disease has the word ‘sclerosis’ in the name, as ‘sclerosis’ means hardening [7]. When this damage occurs in areas near the pons and on the trigeminal nerve, it can give rise to symptoms of TN. TN caused by MS shows similar relative statistics to the idiopathic kind – they are both more prevalent in women and more often present on the right side of the face than the left [8].

 

Symptoms and Diagnosis 

The main identifying characteristic of TN is brief, intense, stabbing pains on the face that are paroxysmal (sudden, lasting for a few seconds and a few minutes at most). They are usually unilateral (on one side of the face) and can very rarely be bilateral (on both sides of the face) but even then the pain does not often occur simultaneously on both sides. If the pain is bilateral, there could be some underlying disease such as MS, which could irritate the nerve on both sides [9]. Furthermore, although the pain can occur spontaneously, there are very few, if any, cases of TN that do not have stimulus-evoked pain as well; most cases have a combination of both [9]. Stimuli in the sensory areas which the trigeminal innervates, such as even a light touch, can cause the pain to occur.

The diagnostic criteria for TN revolve around these symptoms and combining them with the use of scans allow doctors to discern what is causing the pain. Doctors do a neurological differential diagnosis: they match the symptoms up with the various disorders, which could be causing them, and then using various tests, clinical experience, and patient history, they can eliminate the most unlikely causes [6]. In the case of TN, the main criterion is paroxysmal and sharp pain [6]. Then the doctors differentiate between symptomatic and classic. The patient history and details of the patient are incredibly useful, for example, patients under 40 are generally unlikely to have the classic form of TN and the patient’s age can be used to discern the likelihood of this [6]. Scans are done using magnetic resonance imaging (MRI) or a computed tomography (CT) scan, which can give vivid images of the brain and can identify if there is a tumour, or some scans can identify if there is a blood vessel compressing the nerve. Throughout this process, the various potential causative diseases can be ruled out, for example, cluster headaches could cause pain, but if they last a longer period of time and are in non-trigeminal areas, then they can be ruled out as the cause [6]. This may seem simplistic and obvious, however, when the symptoms are less conspicuous, differential diagnosis becomes all the more important. For example, more subtly, in TN, the physical examination is usually normal so an abnormal physical exam relating to the pain can suggest another cause [6]. After considering all of these factors, a physician can come to a final diagnosis.

The pain is also responsible for some psychological symptoms of the disease; TN has been referred to as the ‘suicide disease’ [10]. The excruciating pain caused by TN can be debilitating and its severity can cause psychological distress.  Some studies have drawn an association between TN and psychiatric disorders, for example, a study by Wu et al., doctors and information specialists in Taiwan, has shown that within the patients they observed, there was a higher risk of developing anxiety and depressive disorders if the patients had TN [11].

 

Treatment 

In the past, a lot of experimentation was done to treat this sort of facial pain. Research and discoveries have assisted the development of treatment alongside experimentation. After 1820, the trigeminal nerve was discriminated from the facial nerve and then surgery began to play a larger role in treatment. Surgeons have tried many different techniques, including neurotomy (cutting the nerve) and neurectomy (removing all or part of the nerve) which were often unsuccessful at the time [2]. Since then, the evolution of surgery and medicine has increased the success rate and allowed TN to be treated and controlled. 

The first line of treatment is the use of medication. Carbamazepine, an anticonvulsant (reduces the instances of involuntary movement) and analgesic (helps to relieve pain) drug, is initially administered to control the symptoms of TN [1]. Other anticonvulsants and analgesics can be prescribed if the patient is allergic or the medication does not work. The psychological symptoms that come alongside the disorder such as depression can be treated by administering antidepressants [12].

 If medication has little effect, then surgical treatment can be considered to reduce the passage of pain signals through the nerve. In the classical form, when it is a vessel that is compressing the nerve, there is a type of surgery known as microvascular decompression (MVD) which can be done laparoscopically (through a small incision with small camera and tools inserted through) [14] (see left). The offending vessel is approached and a sponge is placed between the trigeminal nerve and the vessel to create relief from pain [14]. Another effective surgery for the disease is stereotactic (precision positioning of surgical equipment) radiosurgery. This involves using a so-called knife ‘made out of’ radiation to target fibres in the trigeminal nerve and damaging them in order to halt or reduce transmission of pain signals [14]. Radiation is focused onto one point by using around 200 beams from different directions. Individually, the beams have little impact on the tissue they pass through, however, the point where they intersect receives a very large quantity of radiation and can be damaged in a very targeted way[15] (see below). Unlike microvascular decompression, it does not tackle the problem as its root cause, but instead, attempts to prevent the pain signals traveling at all. This is a non-invasive surgery so it means the patient does not have to be under general anaesthesia (to make them unconscious during surgery) and therefore is of benefit for those unwilling to go under general anaesthesia or are medically unable to do so [14]. Other procedures that aim to treat TN by destroying fibres in the trigeminal nerve are called percutaneous (through the skin) stereotactic destructive procedures. An example of this is when an electrode is passed through the skin to a portion of the trigeminal nerve. When a heating current is passed through the electrode, it can destroy some nerve fibres in the trigeminal nerve. This can cause a degree of facial numbness but this is important for recovery from the painful symptoms of the condition [14].

 

Future Prospects

One of the main avenues of future treatment for TN is designing specific drugs to target the pain specifically and reduce it substantially. Current drugs are useful in controlling pain but not getting rid of it completely. A new drug known as BIIB074 is in the trial for TN and other chronic pain conditions[17]. In pain-causing conditions such as TN, it is the opening of sodium channels that allows for the transmission of pain signals. There is especially a large number of a type called sodium channel 1.7 in pain-causing nerves. This new drug acts in a way that blocks these channels. The drug also increases the strength of blocking the more active the channel gets. This allows greater levels of blocking where there is more transmission; where the pain signals are being sent. It targets the area of pain and mitigates the side effects that come with some other drugs that act on sodium channels no matter their activity levels [17].

 

Conclusion 

TN is a unique, severe pain condition that affects the face. It is a result of irritation of the trigeminal nerve which is one of the main nerves that originate in the brain -specifically the brain stem. In TN, it is interesting that even though the pain may be perceived as physical, there is a huge psychological component to the disease - supporting that there is a link between psychological and physical pain in the body. It is hard to diagnose and the characteristic pain could be due to a whole host of different factors thus TN is by no means the most likely. However, with specialist diagnosis, it can be identified and tackled. Techniques to treat TN have developed over time and mitigated the consequences of early forms of treatment, for example, complete facial numbness caused by neurotomy. Now with modern drugs and surgeries, doctors can target treatments to the specific fibres that cause pain.


References


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Aviral Batra

Aviral Batra


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