Blink reflex in trigeminal hypoesthesia caused by a pontine demyelinating lesion

Abstract

Sirs: The blink reflex (BR) test evaluates the integrity of the trigeminalfacial arc. Unilateral electrical stimulation of the supraorbital nerve evokes two separate contractile responses in the orbicularis oculi muscle. The early (R1) component is evoked only on the side of stimulation as a pontine reflex, whereas the late (R2) component is recorded bilaterally and is presumed to be relayed through polysinaptic pathways of the pons and the lateral medulla. We report a case of trigeminal hypoesthesia with abnormalities in the BR demonstrative of a pontine lesion which was correlated with the lesion identified by magnetic resonance imaging (MRI).A 38-year-old woman was diagnosed as suffering from myasthenia gravis. She had a positive tensilon test, decremental response to repetitive stimulation of the cubital nerve, positive single-fiber electromyography in the extensor digitorum communis muscle, and positive anti-acetylcholine receptor antibodies. Her clinical evolution showed tactile hypoesthesia with dysesthesias in the three branches of the right trigeminal nerve to the vertex. Examination showed a tactile sensory deficit in the territory of this nerve with absent corneal reflex. There was no motor involvement. The remainder of the neurological examination was normal. The following neurophysiological tests were carried out: BR, somatosensory evoked potentials (SEPs) on both trigeminal nerves and brainstem auditory evoked potentials (BAEPs). BR recordings (Fig. 1) showed an absent R1 component to right supraorbital nerve stimulation, with normal R2 components latencies bilaterally and a normal latency of R1, R2I, and R2, C components to left supraorbital nerves stimulation. The SEP of the left trigeminal nerve was normal (P1:20 ms). No response to stimulation of the right side was be recorded. BAEPs showed a 0.4-ms relative prolongation of the III-V interpeak latency to right ear stimulation. Based on the results of the electrophysiological tests a subsequent cranial MRI was performed which showed an area of high signal intensity approximately 4.2 mm in diameter in the caudal part of the right pontine tegmentum (Fig. 2). This lesion corresponded to the location of the principal trigeminal sensory nucleus and spared the intra-axial mixed sensory and motor trigeminal nerve fascicles. This is a case of Kimura's third pattern [7]. The restriction of the BR abnormality to the R1 component in-LETTER TO THE EDITORS Fig. 1 A, B Blink reflex. A Absence of R1 in the right side with normal R2I and R2 C. B Normal R1, R2I, and R2C in the left side

Cluster headache attacks and multiple sclerosis

“…In our opinion, there is evidence in favour of a relation between the two pathologies: the MRI of the demyelinating lesion showed that it was located exactly in the trigeminal nerve root inlet area, thus involving the trigeminovascular circuit. In addition the anomalies of the blink reflex are also consistent with the presence of a lesion in the pontine trigeminal nucleus [8].…”