Abnormalities of the blink reflex in burning mouth syndrome

Abstract

To our knowledge, this is the first report on pain-related abnormalities of the eye blink reflex (BR) in a clinical pain patient population. The objective of this study was to evaluate the possible neuropathic mechanisms underlying the burning mouth syndrome (BMS), by means of objective electrophysiological examination of the trigemino-facial system. We studied the BR with stimulation of the supraorbital nerve (SON) with particular emphasis on the occurrence of the pain-related ultralate R3 components, and the habituation response of the R2 components. The subjects consisted of eleven BMS patients and 10 healthy control subjects. All patients underwent thorough clinical oral and neurological examinations. The motor function of the trigeminal nerve was assessed with a jaw reflex recording, and a needle-EMG examination of the facial and masticatory muscles was performed in the patients with abnormalities in the BR recordings. The jaw reflexes, the latencies of the BR components, and the needle-EMG examinations were normal in all patients. As a group, the BMS patients had statistically significantly higher stimulus thresholds for the tactile R 1 components of the BR compared with the control subjects. With non-noxious stimulation, the BMS patients showed more frequently pain-related R3 components (11/22 SONs) compared with the controls (3/20 SONs). In addition, four BMS patients had abnormal habituation of the R2 components. In two of these patients, the findings were segmental (i.e., unilateral), coinciding with the side of the subjective BM symptoms. The abnormalities of the BR tests appeared to be related to longer disease duration. Our results suggest a possible pathologic involvement of the nervous system in chronic BMS.

Etiology of burning mouth syndrome: A review and update

“…The existence of an enhanced blink reflex in some patients with BMS points to a central nervous system alteration correlated to dopaminergic system dysfunction (9). Diminished presynaptic dopaminergic inhibition would increase dopamine release into the interneuronal space, with enhanced neuron excitability manifesting as an increased blink reflex (9,12). Posteriorly, dopaminergic system dysfunction was confirmed in patients with BMS on evaluating dopaminergic function in the brainstem of such patients (13), and on observing a decrease in endogenous dopamine levels in the putamen of individuals with BMS (14).…”

“…Based on the existing evidence, menopause can be associated to an increased risk of developing BMS (7). This hypothesis in turn is supported by the good results obtained with oral hormone (estrogen) replacement therapy in application to the symptoms of xerostomia (8). 3.-Lastly, the presence of sensory alterations such as changes in heat tolerance, reduced and altered taste sensation, and increased excitability of the blink reflex in patients with BMS points to the existence of a biological basis related to alterations of both the central and peripheral nervous system (9,10). At present, BMS is regarded as a painful condition involving neuropathic mechanisms, as evidenced by the burning nature of the pain.…”

“…It therefore may be postulated that BMS is a consequence of both generalized alterations and disorders at different levels of the trigeminal system (11). The existence of an enhanced blink reflex in some patients with BMS points to a central nervous system alteration correlated to dopaminergic system dysfunction (9). Diminished presynaptic dopaminergic inhibition would increase dopamine release into the interneuronal space, with enhanced neuron excitability manifesting as an increased blink reflex (9,12).…”

Salivary and serum levels of substance p, neurokinin A and calcitonin gene related peptide in burning mouth syndrome

“…Likewise, reduced levels of NKA in the serum of patients with BMS may reflect a deficiency in the dopaminergic system and some commentators have suggested that such a deficient dopaminergic influence might actually be causative in BMS (11). Electrophysiological examinations in BMS patients indicate an abnormal blink reflex which is under control of dopaminergic inhibitory control through the basal ganglia connection with the facial motor nuclei (12). An abnormal blink reflex is also a common finding in extra-pyramidal disorders such as Parkinson's disease and facial dyskinesias (13,14) where it may be caused by a deficient dopaminergic influence on the brainstem nuclei.…”

Neurophysiological assessment of craniofacial pain

“…Several studies used quantitative sensory testing, electrophysiological methods and functional neuroimaging to assess trigeminal sensory function in patients with BMS: some investigators demonstrated abnormalities of trigeminal pathway function, thus indicating a possible neuropathic aetiology of BMS [48,49]. In a recent study, Lauria and coworkers [50] investigated innervation of the epithelium of the tongue in superficial biopsies from 12 patients who had a 6-month history of clinically definite BMS and healthy persons.…”