Note that diagnosis with IHS codes 13.18.1, 13.18.4, and 13.18.5 may have peripheral causes.

World Health Organization (WHO) code and diagnosis: G 44.810 or G44.847. Central causes of facial pain.

Short description: Central pain: The International Association for the Study of Pain (IASP) has defined central pain as pain caused by a lesion or dysfunction in the central nervous system (CNS) (26). Thus, peripherally induced pain with central mechanisms is not central pain, even if the central mechanisms are prominent. Central pain is usually constant and spontaneous, but evoked and paroxysmal pain occur in a minority of patients.

Other terms: Thalamic pain is often used in a general sense for all central pain. Pseudothalamic pain is then sometimes used for central pain caused by extrathalamic lesions. Central poststroke pain in the revised International Classification for Headache Disorders (ICHD-II: 13.18.2) denotes central pain resulting from a cerebrovascular lesion (CVL) affecting the “quintothalamic pathway or thalamus.” Dysesthetic pain sometimes refers to central pain with a predominantly dysesthetic character, but such pain can have either central or peripheral causes.

Anesthesia dolorosa denotes pain in a region with decreased sensibility after lesions in the CNS or peripheral nervous system (PNS). The term deafferentation pain is used for similar conditions, but it is more commonly used in patients with lesions of spinal nerves.

The prevalence of central pain varies depending on the underlying disorder (Tables 128-1 and 128-2) (7,29). In the absence of large scale epidemiologic studies, only estimates of central pain prevalence can be quoted.

In the only prospective epidemiologic study of central pain, 191 patients with central poststroke pain (CPSP) were followed for 12 months after stroke onset (1). Sixteen (8.4%) developed central pain, an unexpectedly high incidence. Among patients with somatosensory deficits (42% of all stroke patients), the incidence of central pain was 18%. These data contrast with figures obtained from a retrospective study of 63 patients with brainstem infarcts (24): central pain was reported in 44%, CPSP in 25%.

In two studies of central poststroke pain, 33% of 27 patients and 37% of 111 patients had facial pain, respectively, in addition to pain at other sites (9,23). In a mixed material of 73 patients with “central pain of brain origin,” 11% had facial pain (30).

In a recent study of 364 patients with multiple sclerosis (MS), a prevalence of 27.5% was found (A. Österberg and J. Boivie, in preparation). This includes 4.9% who had trigeminal neuralgia, which in this context is considered to be a central pain condition because it is caused by an inflammatory lesion located in the CNS (Tables 128-1 and 128-2).

Brain tumors and traumatic brain injuries seldom cause central pain (25,30).

About 3% of patients with spinal anterolateral cordotomy develop late-onset central pain, usually of a
dysesthetic nature (19,25,30). On the other hand, mesencephalic and pontine tractotomies might carry an even higher risk of central pain (29).

Systematic genetic studies of central pain have not been conducted; nevertheless, a genetic predisposition is suspected. In humans, similar lesions lead to central pain with some people, but not in others. In rats, experimental nerve lesions cause neuropathic pain in some strains, but not in others (15).

Table 128-1 lists diseases and lesions commonly associated with central pain. These include rapidly developing lesions such as parenchymal hemorrhage and the slowly developing inflammatory demyelinating lesions of MS. The incidence of central pain differs in different diseases, suggesting that differences in the lesions are important factors. Unfortunately, little is known about these factors at the cellular level, including what happens to transmitter receptors.

Lesion location is an important factor in the genesis of central pain. Central pain develops with lesions of the spino- and quintothalamic pathways (i.e., pathways that are most important for the sensibility of pain and temperature) (4,8,32,38), including the thalamocortical projections (5,7,9,29). Also, a central pain-causing lesion can be located at any level of these pathways along the neuraxis, from the origin of the spinal trigeminal nucleus or the spinal dorsal horn to the cerebral cortex (10).

The first central pain condition to be described in detail was the thalamic pain of Dejerine and Roussy (14). It was viewed as one component of the thalamic syndrome. The thalamic syndrome is usually caused by a thalamic infarction or hemorrhage (18), but in many cases the lesion causing thalamic pain extends considerably laterally to the thalamus. Also, relatively recent data suggest that central pain develops in about 17% of patients with thalamic stroke only if the ventroposterior region is involved (8,23).

Thalamic involvement is not necessary for CPSP. Recent computed tomography (CT) and magnetic resonance imaging (MRI) studies indicate that at most about half of stroke patients with central pain have lesions involving the thalamus (10,23). Both supra- and infrathalamic lesions, including cortical lesions, can cause central pain. For instance, there is good evidence that lesions involving the parietal cortex and the insular and adjacent perisylvian cortex can produce loss of pain and temperature sensibility (4). Brainstem strokes of the Wallenberg type (i.e., infarctions in the region of the posterior inferior cerebellar artery [PICA]) are well known to cause central pain in some patients. In one study, such lesions were present in 8 of 27 consecutive patients with CPSP (23). The risk of developing central pain may be higher with brainstem lesions affecting the quintothalamic pathways than with suprathalamic lesions (24).

Neurosurgical lesions of the quintothalamic tract for the treatment of intractable head pain show that lesions of this pathway in the pons and midbrain can lead to central pain (19,28). Some of these patients develop central pain with a dysesthetic quality several months after the operation.