Orofacial pain
syndromes encompass several clinically defined and classified entities.
The focus here is on the role of clinical neurophysiologic and
psychophysical tests in the diagnosis, differential diagnosis, and pathophysiological mechanisms of definite trigeminal neuropathic pain and other chronic orofacial pain
conditions (excluding headache and temporomandibular disorders). The
International Classification of Headache Disorders 2018 classifies these
facial pain disorders under the heading Painful cranial neuropathies and other facial pains.
In addition to unambiguous painful posttraumatic or postherpetic
trigeminal neuropathies, burning mouth syndrome, persistent idiopathic
facial and dental pain, and trigeminal neuralgia have also been
identified with neurophysiologic and quantitative sensory testing
to involve the nervous system. Despite normal clinical examination,
these all include clusters of patients with evidence for either
peripheral or central nervous system pathology compatible with the
subclinical end of a continuum of trigeminal neuropathic pain
conditions. Useful tests in the diagnostic process include
electroneuromyography with specific needle, neurography techniques for
the inferior alveolar and infraorbital nerves, brain stem reflex
recordings (blink reflex with stimulation of the supraorbital,
infraorbital, mental, and lingual nerves; jaw jerk; masseter silent
period), evoked potential recordings, and quantitative sensory testing.
Habituation of the blink reflex and evoked potential responses to
repeated stimuli evaluate top-down inhibition, and navigated
transcranial magnetic stimulation allows the mapping of reorganization
within the motor cortex in chronic neuropathic pain. With systematic use of neurophysiologic and quantitative sensory testing, many of the current ambiguities in the diagnosis, classification, and understanding of chronic orofacial syndromes can be clarified for clinical practice and future research.