Neuropathic pain refers to pain emanating from the nerves. Neuropathic pain disorders are a set of conditions which result either from a disorder or an injury to the nervous system.  The human nervous system is composed of two parts. The first is the central nervous system which consists of the brain and spinal cord.  The second is the peripheral nervous system which conveys nerves to the trunk, limbs, face and the outlying areas of the body. Injury to the nerves of the central or peripheral nervous system can cause pain signals to be sent to the brain, which can result in a chronic pain condition referred to as neuropathic pain.

Neuropathic pain may manifest itself as continuous or episodic. Neuropathic orofacial pain refers to those symptoms that primarily affect a patient’s mouth and facial area.

Episodic neuropathic pain is described as a very intense, quick, sharp, electric-like debilitating pain. The pain follows the distribution of the affected nerve. One of the most diagnosed and well known episodic neuropathic pains is trigeminal neuralgia (TN).  TN is characterized by sudden, usually unilateral, severe electrical like stabbing episodes of pain, followed by total remission of symptoms.  Attacks usually last from a fraction of a second to two minutes. Causes of TN include:  nerve compression, tumors, multiple sclerosis and physical injury.  TN is commonly brought on by non-noxious stimuli (i.e., washing or touching the face, wind on the face, talking, brushing teeth, etc.) and can also occur spontaneously. There are other episodic neuropathic conditions that are much less common such as: glossopharyngeal neuralgia, geniculate neuralgia, superior laryngeal neuralgia, nervous intermedius neuralgia and occipital neuralgia.

Continuous neuropathic pain is described often, as a dull, yet burning type pain. The pain is usually ongoing and unremitting, yet the intensity can show patterns of fluctuation. It is also usually accompanied by other neurological signs (i.e., an increase or decrease in pain perception, etc.). One of the most common and well known continuous forms of neuropathic pain is atypical odontalgia (AO).  AO is a poorly understood chronic pain disorder that is best defined as a persistent pain in apparently normal teeth and adjacent oral tissues (i.e., bone and gum tissue), in the absence of any signs of pathology. It can also occur in a site from which a tooth has been extracted (phantom teeth). AO disorders are characterized by constant pain without any periods of remission. The pains are of variable intensity, ranging from mild to severe, but are not as excruciating as the pain of trigeminal neuralgia. The quality of pain is usually described as dull and aching, and is often accompanied by burning or throbbing components. A high proportion of the patients precipitating factors include traumatic injury and various routine dental procedures.  Suspected causes are: psychological, neurovascular, or interruption or destruction (i.e., being cut or compressed) of the nerves.  Other occurring but maybe not as common continuous neuropathic conditions are: Bell’s palsy, herpes zoster, burning mouth syndrome, postherpetic neuralgia, complex regional pain syndrome, etc.

Diagnosis

Various orofacial neuropathies derive from a number of causes. Therefore, depending on the symptoms experienced, the diagnostic process often varies.  As with any diagnostic process, it is most important for a doctor to take a complete medical history and description of the symptoms, perform a thorough physical exam, and order any necessary tests or scans (i.e., magnetic resonance imaging (MRI), magnetic resonance angiography (MRA), dental x-rays, nerve blocks, electromyogram (EMG), etc).  Some neuralgias are often diagnosed by eliminating other serious medical problems, and ruling out other possible causes.

Treatment

Fortunately, for those suffering from facial neuropathies, while much is unknown about these conditions and their causes, a number of treatments have been found to be effective. A combination of treatments and therapies is often found most effective in managing orofacial neuropathic pain symptoms, such as: palliative treatment, physical therapy, a variety of medications and their delivery systems, injections again using a variety of medicaments, and different types of surgical procedures, etc.

Intraoral (inside the mouth) pain potentially has many sources. Any of the numerous structures within the oral cavity can elicit pain, and therefore, any evaluation for pain in the head, face or jaw should include an exam of the oral cavity. An orofacial pain specialist must work closely with other dentists when assessing causes for intraoral pain. The muscles, nerves, blood vessels, TMJ, TMJ disc, tendons and other structures of the face, jaws, head and neck have the potential to refer pain into the oral cavity. Also, structures within the oral cavity have the potential to refer pain outside of the mouth. All areas must be evaluated to arrive at an accurate diagnosis. See the “Chronic Pain” section for a definition of referred pain.

The most common source of orofacial pain is from intraoral structures. Some common sources for intraoral pain include the teeth, teeth nerves, bone around the teeth, mucogingival tissues (gums, soft tissues of cheeks, palate, under the tongue), salivary glands, and tongue.

Common disorders associated with these various structures:

Pulpal pain – this is pain from the nerve of the teeth. The most likely causes are large cavities, fractured teeth and infected/abscessed teeth.

Periodontal pain – pain from the periodontal ligament (ligament that binds the tooth to the bone) or alveolar bone (bone in which the tooth root is attached). The causes can be bacterial infections causing abscessing of these tissues or trauma to these tissues.

Mucogingival pain – mucogingival pertains to the tissue lining the inside of the cheeks and palate, covering of the floor of the mouth under the tongue, and the gingiva (gums) around the teeth. Pain to these areas may be a result of bacterial infection of the gingiva, aphthous ulceration (canker sores), herpes simplex viral vesicles in the mouth, candidiasis (an oral fungal infection), trauma to the tissues, mucogingival cancer, or burning mouth syndrome (BMS). BMS may cause a generalized burning sensation to the mucogingival tissues in the mouth and the tongue.

Xerostomia – excessive dry mouth that may lead to pain. The possible causes includes an extensive list, which are too numerous to list in this context. An individual with undiagnosed xerostomia may need a comprehensive examination by an oral medicine specialist.

Glossal pain – pain of the tongue. Burning mouth syndrome (as listed above), infections of the tongue and trauma are common sources of glossal pain. Benign migratory glossitis is another condition of the tongue that may cause pain or burning. It is benign, as listed in the name, and is of an unknown cause, but results in discolored, smooth patches on the tongue that tend to move around over time (“migrate”). These areas may be tender or painful when eating spicy food.

Chronic pain is defined by the American Academy of Orofacial Pain (AAOP) as “Pain that persists when other aspects of disorder-disease have resolved, typically lasting more than 6 months or beyond the normal time for healing of an acute injury or pain”. In other words, the pain persists even when the initial reason for the injury or pain has stopped.

The exact mechanisms as to why some pain conditions heal normally and others develop into chronic pain are very complex and not completely understood by science. There are researchers around the world investigating the complexities of chronic pain. Though we have many answers, volumes of text books, and useful therapies for chronic pain, we are far from a full understanding.

Once the initial injury or insult to the bodies’ tissues (muscles, nerves, bones, blood vessels, etc.) has ended and an appropriate healing time has elapsed, yet the pain persists, the pain has become “chronic pain”. Chronic pain involves physical changes in the brain, spinal cord and the nerves and nerve junctions all the way from the brain to the pain site. This shift results in the pain source that was outside of the body, to now the pain being generated from within the body by the Autonomic Nervous System (ANS). These deviations also change how the brain and rest of the body process information to the body from outside sources (trauma, touch, hot, cold, etc.), particularly that of pain. Once these variations have occurred, treating the original pain source will be insufficient to alleviate the pain as treatment for chronic pain may be different than that for acute pain. The initial step toward managing chronic pain is obtaining a thorough evaluation with a qualified orofacial pain specialist. The earlier a chronic pain condition is treated, the more likely the outcome will be positive. The following are aspects of chronic pain that an individual may experience:

Referred pain – this type of pain is common with chronic conditions and is defined as pain in an area that is different from the site or the source of pain. For example; a person may have pain in a tooth, but the actual source of the pain may be an inflamed jaw muscle that is projecting pain to the tooth. The most well-known example of referred pain is that of during a heart attack the first pain experienced may be left arm pain or jaw pain.

Hyperalgesia – this is an elevated pain sensation to something that is normally painful. For example; a strong slap on the back can be uncomfortable or mildly painful, but a person with chronic pain and hyperalgesia may experience severe pain to the same slap on the back.

Allodynia – this is a painful response to an event that normally does not cause pain. For example; a hug from a friend does not typically elicit pain, though some individuals experience pain to simple gestures such as a hug, holding hands, a touch to the arm, chewing, talking, or singing.