Clinical Neurophysiology and Quantitative Sensory Testing in the Investigation of Orofacial Pain and Sensory Function

Chronic orofacial pain represents a diagnostic and treatment chal-lenge for the clinician. Some conditions, such as atypical facial pain, still lack proper diagnostic criteria, and their etiology is not known. The recent development of neurophysiological methods and quantitative sensory testing for the examination of the trigemi-nal somatosensory system offers several tools for diagnostic and etiological investigation of orofacial pain. This review presents some of these techniques and the results of their application in studies on orofacial pain and sensory dysfunction. Clinical neuro-physiological investigation has greater diagnostic accuracy and sen-sitivity than clinical examination in the detection of the neurogenic abnormalities of either peripheral or central origin that may under-lie symptoms of orofacial pain and sensory dysfunction. Neurophysiological testing may also reveal trigeminal pathology when magnetic resonance imaging has failed to detect it, so these methods should be considered complementary to each other in the investigation of orofacial pain patients. The blink reflex, corneal reflex, jaw jerk, sensory neurography of the inferior alveolar nerve, and the recording of trigeminal somatosensory-evoked potentials with near-nerve stimulation have all proved to be sensitive and reli-able in the detection of dysfunction of the myelinated sensory fibers of the trigeminal nerve or its central connections within the brain-stem. With appropriately small thermodes, thermal quantitative sensory testing is useful for the detection of trigeminal small-fiber dysfunction (A
and C). In neuropathic conditions, it is most sensi-tive to lesions causing axonal injury. By combining different tech-niques for investigation of the trigeminal system, an accurate topo-graphical diagnosis and profile of sensory fiber pathology can be determined. Neurophysiological and quantitative sensory tests have already highlighted some similarities among various orofacial pain conditions and have shown heterogeneity within clinical diagnostic categories. With the aid of neurophysiological recordings and quantitative sensory testing, it is possible to approach a mecha-nism-based classification of orofacial pain.

neurophysiological diagnostic techniques; neuropathy; orofacial pain; quantitative sensory testing; trigeminal nerve

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