Title: Unusual blink reflex: Absent r1 response on ipsilateral supraorbital nerve stimulation but present during contralateral stimulation
Abstract: Background: Early or R1 motor response from the orbicularis oculi (o. oculi) muscle is obtained only unilaterally from ipsilateral supraorbital nerve stimulation, while the late or R2 response is present bilaterally during ipsilateral and contralateral stimulation. Case material: A 29-year-old woman developed horizontal diplopia, left facial numbness, and occasional left eyelid twitching. Otherwise, she was healthy. Examination showed left 6th cranial nerve palsy and decreased left facial sensation. There was no blepharospasm, myokymia, or facial weakness. Electrophysiologic findings: Peripheral motor nerve conduction study of both facial nerves and needle EMG of left facial muscles showed no abnormality. Blink reflex study revealed no R1 response from the left o. oculi muscle on ipsilateral supraorbital nerve stimulation, but present during contralateral stimulation (latency = 11.4 ms). R2 responses from the left o. oculi muscle showed normal latencies during contralateral (31.2 ms) and ipsilateral stimulation (30.8 ms) stimulation. R1 latency from the right o. oculi muscle was 10.0 ms, and the R2 responses showed normal latencies during contralateral (31.0 ms) and ipsilateral (31.9 ms) stimulation. Conclusions: Absent R1 response during ipsilateral stimulation suggests abnormalities in the main sensory nucleus of the pons. Presence of an R1 response from the o. oculi muscle during contralateral supraorbital nerve stimulation is unusual. This may indicate cross excitation of the facial nucleus from contralateral trigeminal sensory nerve impulses that are not involved in the usual multi-synaptic pathways responsible for eliciting the R2 contralateral response. Perhaps this is a result of focal CNS demyelination.