Pain in trigeminal neuralgia: neurophysiology and measurement: a comprehensive review

Abstract

Trigeminal neuralgia (TN) is defined as sudden, usually unilateral, severe, brief, stabbing recurrent episodes of pain within the distribution of one or more branches of the trigeminal nerve. It is the most frequent cranial neuralgia, the incidence being 1 per 1,000,00 persons per year. Pain attacks start abruptly and last several seconds but may persist 1 to 2 minutes. The attacks are initiated by non painful physical stimulation of specific areas (trigger points or zones) that are located ipsilateral to the pain. After each episode, there is usually a refractive period during which stimulation of the trigger zone will not induce the pain. According to the European Federation of Neurological Societies (EFNS) guidelines on neuropathic pain assessment and the American Academy of Neurology (AAN)-EFNS guidelines on TN management the neurophysiological recording of trigeminal reflexes represents the most useful and reliable test for the neurophysiological diagnosis of trigeminal pains. The present article discusses different techniques for investigation of the trigeminal system by which an accurate topographical diagnosis and profile of sensory fiber pathology can be determined. With the aid of neurophysiological recordings and quantitative sensory testing, it is possible to approach a mechanism-based classification of orofacial pain.

Keywords: neurophysiology; pain assessment; quantitative sensory testing; trigeminal neuralgia.

Fig. 1

Convergence of primary small fibres subserving nociception

Fig. 2

Trigeminal reflexes for diagnosing symptomatic trigeminal neuralgia One early response is measured for each of the three trigeminal divisions: the R1 blink reflex after stimulation of the supraorbital nerve (V1-R1), the SP1 masseter inhibitory reflex after stimulation of the infraorbital nerve (V2-SP1) and that after stimulation of the mental nerve (V3-SP1). Figure shows surface recordings from the orbicularis oculi muscle (for V1) and masseter muscle for (V2 and V3).

Fig. 3

Visual Analog Scale

Fig. 4

Visual Analog Scale

Table 1

Barrow Neurological Institute Pain Intensity Score

Table 2

McGill Pain Questionnaire

Table 3

Initiative on Methods, Measurement and Pain Assessment in Clinical Trials Recommendations for Core Outcome Measures

Fig. 5

Brief Pain Inventory Scale

Table 4

BPI-Facial scale