Atypical facial pain (AFP) is a type of chronic facial pain which does not fulfill any other diagnosis. There is no consensus as to a globally accepted definition, and there is even controversy as to whether the term should be continued to be used. Both the International Headache Society (IHS) and the International Association for the Study of Pain (IASP) have adopted the term persistent idiopathic facial pain (PIFP) to replace AFP. In the 2nd Edition of the International Classification of Headache Disorders (ICHD-2), PIFP is defined as "persistent facial pain that does not have the characteristics of the cranial neuralgias ... and is not attributed to another disorder." However, the term AFP continues to be used by the World Health Organization's 10th revision of the International Statistical Classification of Diseases and Related Health Problems and remains in general use by clinicians to refer to chronic facial pain that does not meet any diagnostic criteria and does not respond to most treatments.
The main features of AFP are: no objective signs, negative results with all investigations/ tests, no obvious explanation for the cause of the pain, and a poor response to attempted treatments. AFP has been described variably as a medically unexplained symptom, a diagnosis of exclusion, a psychogenic cause of pain (e.g. a manifestation of somatoform disorder), and as a neuropathy. AFP is usually burning and continuous in nature, and may last for many years. Depression and anxiety are often associated with AFP, which are either described as a contributing cause of the pain, or the emotional consequences of suffering with unrelieved, chronic pain. For unknown reasons, AFP is significantly more common in middle aged or elderly people, and in females.
Atypical odontalgia (AO) is very similar in many respects to AFP, with some sources treating them as the same entity, and others describing the former as a sub-type of AFP. Generally, the term AO may be used where the pain is confined to the teeth or gums, and AFP when the pain involves other parts of the face. As with AFP, there is a similar lack of standardization of terms and no consensus regarding a globally accepted definition surrounding AO. Generally definitions of AO state that it is pain with no demonstrable cause which is perceived to be coming from a tooth or multiple teeth, and is not relieved by standard treatments to alleviate dental pain.
Depending upon the exact presentation of atypical facial pain and atypical odontalgia, it could be considered as craniofacial pain or orofacial pain. It has been suggested that, in truth, AFP and AO are umbrella terms for a heterogenous group of misdiagnosed or not yet fully understood conditions, and they are unlikely to each represent a single, discrete condition.
Signs and symptoms Some sources list some non-specific signs that may be associated with AFP/AO. These include increased temperature and tenderness of the mucosa in the affected area, which is otherwise normal in every regard.
Patient often reports symptoms of paresthesia, pain, and throbbing. Physical examination may be normal, but hypoesthesia, hyperesthesia, and allodynia may be found.
The features of atypical facial pain can be considered according to the Socrates pain assessment method (see table).
Parameter Usual findings in atypical facial pain/atypical odontalgia Site The pain is often poorly localized, but is usually located in the region of the maxilla (upper jaw), which is affected more than the mandibular region, although sometimes both may be affected. The pains location does not correlate to the anatomic distribution of trigeminal nerve, and may be located unilaterally (more usually) or bilaterally. Sometimes the pain may be seem to be located in a tooth that has been previously extracted, or associated with a previous surgical procedure. Over time the pain may migrate, spontaneously or as a response to interventions, to other sites, or slowly expand. Where the teeth are involved, usually a whole quadrant is affected. Onset Usually present continuously for months or years, with intermittent periods of increased pain, and an overall gradual increase in pain over time. Sometimes the onset may be mistakenly attributed by the individual to a dental procedure in the past. Character Usually described as dull, aching pain. Sometimes the pain is hard to describe, and affected individuals resort to emotive words to describe the pain. Other descriptions include "gripping", "gnawing", "nagging", "vice-like", "crushing", "burning", "deep" or "pressure". Radiation The pain may radiate in anatomically impossible ways, e.g. crossing anatomic borders such as dermatomes or the midline. AFP may extend to involve the temple, neck, or occipital region (the back of the head). Associations There is a strong association with depression and anxiety. Sometimes other conditions may be associated, such as irritable bowel syndrome, neck pain, back pain, pelvic pain, fibromyalgia, subjective xerostomia (a dry mouth symptom with no identifiable cause), dysgeusia (bad taste), headaches, dysmenorrhea (excessive period pains), Chronic fatigue syndrome, or Dyspepsia. Time course Pain is continuous throughout the day, or less commonly may be intermittent. Exacerbating/Relieving factors No usual precipitating or relieving factors. Notably simple analgesics do not usually relieve the pain and there are no "trigger zones" (as with trigeminal neuralgia). Facial movements also do not usually trigger the pain. Stress can make the pain worse. Severity The intensity is variable, but usually described (by clinicians) as moderate to severe, and may be as severe as trigeminal neuralgia (but the pain is of different character, especially with regards AFP usually being continuous rather than the paroxysmal pain seen in trigeminal neuralgia). Effect on sleep AFP does not usually wake people from sleep. Previous treatment Possibly multiple failed attempts at previous medical and/or dental treatment, e.g. tooth extraction. Sometimes a treatment may provide temporary relief, only for the pain to return days or weeks later, or in a different part of the face.
Causes
Health care associated Sometimes dental treatment or surgical procedures in the mouth appear to precede the onset of AFP, or sometimes persons with AFP will blame clinicians for their pain.
Organic disease
Many persons with AFP blame organic disease for their pain.
Research in individuals with AFP showed that there is increased cerebral activity (demonstrated during positron emission tomography), possibly suggesting that there is an overactive alerting mechanism to peripheral stimuli. It has been theorized that this can trigger neuropeptides to be released, and the formation of free radicals (capable of damaging cells), the release of eicosanoids (e.g. prostaglandins). There is some suggestion that AFP is an early form of trigeminal neuralgia.
Pain may be referred from other parts of the head or other parts of the body to cause facial pain. Nowhere in the body is referred pain more well illustrated than in the face, and this is due to the richly and complexly innervated nature of the head and neck.
"Neuralgia-inducing cavitational osteonecrosis" Neuralgia-inducing cavitational osteonecrosis (NICO) is a controversial term, and it is questioned to exist by many. Osteonecrosis of the jaws refers to the death of bone marrow in the maxilla or the mandible due to inadequate blood supply. It is not necessarily a painful condition, typically there will be no pain at all unless bone necrotic bone becomes exposed to the mouth or through the facial skin, and even then this continues to be painless in some cases. When pain does occur, it is variable in severity, and may be neuralgiform or neuropathic in nature. The term NICO is used to describe pain caused by ischemic osteonecrosis of the jaws, where degenerative extracellular cystic spaces (cavitations inside the bone) are said to develop as a result of ischemia and infarctions in the bone marrow, possibly in relation to other factors such as a hereditary predisposition for thrombus formation within blood vessels, chronic low-grade dental infections and the use of vasoconstrictors in local anesthetics during dental procedures. This proposed phenomenon has been postulated to be the cause of pain in some patients with AFP or trigeminal neuralgia, but this is controversial. NICO is said to be significantly more common in females, and the lesions may or may not be visible on radiographs. When they are visible, the appearance is very variable. About 60% of the lesions appear as a "hot spot" on a technetium 99 bone scan. Proponents of NICO recommend decortication (surgical removal of a section of the cortical plate, originally described as a treatment for osteomyelitis of the jaws) and curettage of the necrotic bone from the cavitation, and in some reported cases, this has relieved the chronic pain. However, NICO appears to show a tendency to recur and develop elsewhere in the jaws. The American Association of Endodontists Research and Scientific Affairs Committee published a position statement on NICO in 1996, stating:
Atypical trigeminal neuralgia Some suggest that AFP is an early form of trigeminal neuralgia.
Psychologic Sometimes stressful life events appear to precede the onset of AFP, such as bereavement or illness in a family member. Hypochondriasis, especially cancerophobia, is also often cited as being involved. Most people with AFP are "normal" people who have been under extreme stress, however other persons with AFP have neuroses or personality disorders, and a small minority have psychoses. Some have been separated from their parents as children.
Depression, anxiety and altered behavior are strongly correlated with AFP. It is argued whether this is a sole or contributing cause of AFP, or the emotional consequences of suffering with chronic, unrelieved pain. It has been suggested that over 50% of people with AFP have concomitant depression or hypochondria. Furthermore, about 80% of persons with psychogenic facial pain report other chronic pain conditions such as listed in the table.
Diagnosis Migraine Dental diseases Neoplasia Infection AFP and AO can be difficult to diagnose, and are often misdiagnosed with resultant inappropriate attempts of treatment, e.g. root canal therapy which may at best have only a temporary benefit, or at worst lead to an increase in the pain. Excluding an organic cause for the pain is the most important part of the diagnosis. Odontogenic pain should especially be ruled out, since this accounts for over 95% of cases of orofacial pain.
There is considerable symptom overlap between atypical facial pain and temporomandibular joint dysfunction.
The diagnosis of facial pain generally is often multidisciplinary.
Classification AFP has also been described as a medically unexplained symptom, which are thought by some to be largely psychogenic in nature. However, true psychogenic pain is considered to be rare. Distinction should be made between somatoform disorder, where affected individuals are not inventing the symptom for some benefit, and other conditions like factitious disorder or malingering.
Recent evidence in chronic facial pain research appear to suggest that a proportion of individuals who have been diagnosed with AFP have neuropathic pain,
AFP is described as one of the 4 recognizable symptom complexes of chronic facial pain, along with burning mouth syndrome, temporomandibular joint dysfunction (TMD) and atypical odontalgia. However, there is a degree of overlap between the features of these diagnoses, e.g. between AFP and TMD and burning mouth syndrome.