Key points

Introduction

There has been considerable controversy about the condition currently called persistent idiopathic facial pain (PIFP) by the International Headache Society Classification (ICHD). The term persistent as opposed to chronic is preferred, as it implies that relief may be a possible outcome. It is often called atypical facial pain (AFP). In this text, both terminologies PIFP and AFP are used, but it is assumed that these are the same disorders. It may include more than one condition; for example, atypical odontalgia or persistent dentoalveolar pain. In the neurosurgical literature it has been termed AFP, and Burchiel emphasized that it excludes disorders for which a cause has been identified and that this is a somatoform disorder diagnosed by psychological testing.

The ICHD description is “persistent facial and/or oral pain, with varying presentations but recurring daily for more than 2 hours per day over more than 3 months, in the absence of clinical neurologic deficit.” See Box 1 for criteria.

Patients are diagnosed into this category frequently as an exclusion diagnosis; however, with improved appreciation of the need to take careful history, patients who were previously put in this category may in fact have other identifiable causes of pain, such as neuropathic pain and myofascial pain, and so do not belong here.

The cause remains unknown but it has been suggested that it could be a consequence of deafferentation and central sensitization but is still is not clear if peripheral or central mechanisms are involved. Not surprisingly, psychological factors are identified but these also could be as a consequence of having chronic pain, lack of diagnosis, and attitude of health care professionals. Gustin and colleagues have shown that psychological and psychosocial factors are universal to chronic pain and are no different between patients with orofacial pain relative to diagnosis.

Introduction

There has been considerable controversy about the condition currently called persistent idiopathic facial pain (PIFP) by the International Headache Society Classification (ICHD). The term persistent as opposed to chronic is preferred, as it implies that relief may be a possible outcome. It is often called atypical facial pain (AFP). In this text, both terminologies PIFP and AFP are used, but it is assumed that these are the same disorders. It may include more than one condition; for example, atypical odontalgia or persistent dentoalveolar pain. In the neurosurgical literature it has been termed AFP, and Burchiel emphasized that it excludes disorders for which a cause has been identified and that this is a somatoform disorder diagnosed by psychological testing.

The ICHD description is “persistent facial and/or oral pain, with varying presentations but recurring daily for more than 2 hours per day over more than 3 months, in the absence of clinical neurologic deficit.” See Box 1 for criteria.

Patients are diagnosed into this category frequently as an exclusion diagnosis; however, with improved appreciation of the need to take careful history, patients who were previously put in this category may in fact have other identifiable causes of pain, such as neuropathic pain and myofascial pain, and so do not belong here.

The cause remains unknown but it has been suggested that it could be a consequence of deafferentation and central sensitization but is still is not clear if peripheral or central mechanisms are involved. Not surprisingly, psychological factors are identified but these also could be as a consequence of having chronic pain, lack of diagnosis, and attitude of health care professionals. Gustin and colleagues have shown that psychological and psychosocial factors are universal to chronic pain and are no different between patients with orofacial pain relative to diagnosis.

Epidemiology

A study in primary care in the Netherlands found an incidence rate of 4.4 (95% confidence interval 3.2–5.9) for AFP with a predominance in women of 75% and mean age of 45.5 years (SD 19.6). A review of 97 patients with facial pain attending a neurologic tertiary center in Austria classified 21% as having PIFP. In a UK community-based study, chronic orofacial pain was identified in 7% of the population and these patients often have other unexplained symptoms, such as chronic widespread pain, irritable bowel syndrome, and chronic fatigue, and show high levels of health anxiety, reassurance-seeking behavior, and recent adverse events.

Clinical features

If there is a history of trauma, extensive dental work before pain onset, for example, of 6 months, then the pain may be neuropathic and so should not be classified under this category. Trained staff may be able to establish a more accurate diagnosis that avoids the label of PIFP. Taking a careful history, including family history, social history, and performing psychological testing, is imperative, as comorbidity is common.

Table 1 lists the key features.

Pfaffenrath and colleagues and Zebenholzer and colleagues have both used the ICHD criteria to determine if the criteria are correct and both suggested alterations. Zebenholzer and colleagues put forward very simple criteria for PIFP under which most chronic orofacial pain could be classified.

Investigations

Many of these patients will have had numerous investigations including MRIs and yet is it questionable whether they should have an MRI scan, as these are normal. Lang and colleagues showed that patients with PIFP do not have neurovascular compression of their trigeminal nerve at the route entry zone. However, patients with PIFP have brain morphology changes consistent with those who have chronic pain, but studies suggest that somatosensory processing is not used to maintain the pain. Conditions such as temporal arteritis may need to be excluded in patients older than 50 years by appropriate investigations.

Forssell and colleagues, when comparing patients with trigeminal neuropathic pain with AFP, showed that up to 75% of patients with AFP demonstrated abnormalities on neurophysiological testing. If qualitative sensory testing and neurophysiological recordings are abnormal, this may result in changing the diagnosis to probable neuropathic pain. It is important that these patients have some form of psychological testing, the easiest of which are psychometrically tested questionnaires such as the Brief Pain Inventory–Facial, Hospital Anxiety and Depression Scale, Pain Catastrophizing Scale, and Chronic Graded Pain Scale. These tests often show high levels of disability. A study of German University centers managing chronic facial pain showed that only 32% (6/19) did psychological testing.