13. Painful cranial neuropathies and other facial pains

Introduction
Pain in the head and neck is mediated by afferent fibres in the trigeminal nerve, nervus intermedius, glossopharyngeal and vagus nerves and the upper cervical roots via the occipital nerves. Stimulation of these nerves by compression, distortion, exposure to cold or other forms of irritation or by a lesion in central pathways may give rise to stabbing or constant pain felt in the area innervated.

The cause may be clear, such as infection by Herpes zoster or a structural abnormality demonstrated by imaging, but in some cases there may be no cause apparent for neuralgic pain.
Trigeminal and glossopharyngeal neuralgias present a problem of terminology. When pain is found to result from compression of the nerve by a vascular loop at operation, the neuralgia should strictly be regarded as secondary. Since many patients do not come to operation, it remains uncertain as to whether they have primary or secondary neuralgias. For this reason the term classical rather than primary has been applied to those patients with a typical history even though a vascular source of compression may be discovered during its course. The term secondary can then be reserved for those patients in whom a neuroma or similar lesion is demonstrated.

Definitions of terms used in this chapter1:
Pain: An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.
Neuropathic pain: Pain (qv)caused by a lesion or disease of the somatosensory nervous system.
Central neuropathic pain: Pain (qv) caused by a lesion or disease of the central somatosensory nervous system.

Peripheral neuropathic pain: Pain (qv) caused by a lesion or disease of the peripheral somatosensory nervous system.

Neuropathy: A disturbance of function or pathological change in a nerve or nerves (in one nerve: mononeuropathy; in several nerves: mononeuropathy multiplex; when diffuse and bilateral: polyneuropathy). The term neuropathy is not intended to cover neurapraxia, neurotmesis, section of a nerve, disturbances of a nerve due to transient impact such as a blow, stretching or epileptic discharge (the term neurogenic applies to pain attributed to such temporary perturbations).

Neuralgia: Pain in the distribution of a nerve or nerves. (Common usage, especially in Europe, often implies a paroxysmal quality, but the term neuralgia should not be reserved for paroxysmal pains.)

1. International Association for the Study of Pain: Taxonomy. URL: http://www.iasp-pain.org.