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Classification of Pain

What is pain?

Pain in the head and neck region is a common affliction, affecting between 10 and 50% of the population. Healthy acute pain (nociceptive pain) is a protective reflex in health and stops us damaging ourselves. In addition once injured the increased sensitivity due to inflammation protects the region from unnecessary movement and further trauma to maximise healing capacity (inflammatory pain). If the pain persists beyond the healing phase and becomes chronic pain (neuropathic or dysfunctional pain) then the neural system reporting pain is abnormal and malfunctioning.

Thus pain is a warning sign of tissue being damaged and often protective reflexes will ensue. The facial region contains structures vital for living (eyes for sight, mouth for breathing, communicating and eating, ears for hearing) and of course the essential organ, the brain, is adjacent. Therefore any threat of damage to this region is life threatening and primitive survival instincts initiated. Thus the psychological and physiological consequences of pain in this region are amplified.

Pain in the face and oral region, supplied by the trigeminal nerve, can be particularly distressing and has a significant psychological meaning due to the region’s role in speech, mastication, communication and body image the trigeminal nerve is responsible for the sensory and motor innervation of much of the orofacial region, and takes up the bulk of the sensory cortex of the human mind, which also explains the highly distressing nature of pain in this region.

The International Association for the Study of Pain (IASP 2011) definition of pain as: “an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage”emphasises that pain is part of a pathological process. the cause could be local disease, neurogenic or vascular in nature, or referred from the neck and chest . however, there remains an ill-defined and rare group of facial pains, which manifest themselves despite any discernible pathology. they are frequently termed atypical, idiopathic or non-somatic. although there is no pathological cause for the pain, the sensation felt by the patient is very real.

Patients suffering from these pains are frequently described as having underlying psychiatric disturbances however, the exact aetiology and classification of idiopathic orofacial pains remain a topic of controversy and many debates

What type of pain do you have?

There are several types of pain.

In 1980, Lipton et al estimated that 5–7 million Americans suffer from chronic pain in the face and mouth, and between 25 and 45% are affected at some time of life.

Risk factors for chronic oro-facial pain include chronic widespread pain, age, gender, gender and psychological factors. Most population-based studies have shown that women report more facial pain than men with rates approximately twice as high among women compared to men. In contrast, other studies have found no sex difference in the prevalence of Orofacial pain which may be related to different gender ‘predilection’ for the extensive variety of Orofacial pain conditions.

Chronic trigeminal pain is a particularly complex problem, due in part to the anatomical and pathophysiological challenges provided by the geography, and the lack of clinician training. In addition the functional and psychological impact of these conditions is significant. Many disciplines (GMPs, GDPs, Nursing, Pharmacists, ENT, neurology, neurosurgery, oral surgery) encounter these patients but none to date have specific training in chronic OFP. Access to specialist services remains a real problem for these patients and many are misdiagnosed and poorly treated as a result.

Orofacial pain may be due to various conditions affecting numerous structures including; the meninges, cornea, oral/ nasal/sinus mucosa, dentition, salivary glands and temporomandibular joint. The complexity of the local region significantly challenges clinicians specialising in this area. The region also has several unique neurophysiologic characteristics different from the spinal nociceptive system. The region is supplied by both spinal (C2 and 3) and several cranial nerves (III, V,VII [nervous internedius], IX, X) providing general sensory sensation and several cranial nerves providing special sensory and autonomic supply that may play a role in some pain conditions. The trigeminal nerve has the largest representation in the human sensory cortex providing the main sensory supply to this region. The devastating impact of pain in the region cannot be underestimated and consequences include interruption with daily social function such as eating, drinking, speaking, kissing, applying makeup, shaving and sleeping and in some cases severely compromising the patients self identity.

The International Association for the Study of Pain (IASP), International Classification of Headache Disorders (ICHD-II), The American Academy of Oro facial Pain  and the Research Diagnostic Criteria for Temporomandibular Disorders (RDCTMD). Other lead clinical scientists and clinicians have also published their perceived deficiencies in the published systems and have proposed further modified classifications of orofacial pain. This review aims to highlight the recent debate and continued struggle to attain a consensus on a classification of Oro facial pain. The preferred pragmatic and interchangeable classification used for this study is Woda et al 2005 (Table 6) and RCD (Table 6).

There have been developments in classifying pain. There is recognition that there are three main types of pain based on a mechanistic perspective https://www.painscience.com/articles/pain-types.php 

Health nociceptive (included pin prick pain and inflammatory pain caused by infection or trauma), and two unhealthy pains wherebye pain is no longer a symptom of tissue protection but a disease itself. These include neuropathc pain caused by sensory nerve damage and nociplastic pain which is regarded chronic widespread or fibromyalgia type conditions likely precipitated and perpetuated by the patients’ genetic makeup 

Several resources highlight the main differences between these pain https://www.news-medical.net/health/What-is-the-Difference-Between-Nociceptive-and-Neuropathic-Pain.aspx#:~:text=The%20cause%20of%20nociceptive%20and%20neuropathic%20pain%20is,the%20potential%20to%20cause%20harm%20to%20the%20body. And https://pubmed.ncbi.nlm.nih.gov/29032407/ 

The international classification of headaches has been updated https://ichd-3.org/ 

The first two parts are headaches types and the third type is orofacial pains 

More recently a group representing ICHD3, International headache society and International association of dental research developed a new International classification of orofacial pain  (ICOP) link to ICOP doc 

There are seven groups of diagnoses 

  • Acute dental pain 
  • Temporomandibular disorders 
  • Myogenic 
  • Articular 
  • Neuropathic nerve injury pain 
  • Headache related facial pain (Migraine and trigemino autonomic cehalalgias mainly) 
  • Idiopathic orofacial pain 
  • Burning Mouth Syndrome with and without neurosensory changes 
  • Persistent idiopathic facial and intraoral pain 

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