Spontaneous Plugging of the Horizontal Semicircular Canal With Reversible Canal Dysfunction and Recovery of Vestibular Evoked Myogenic Potentials

Objective: To evaluate the clinical pathophysiology of oculomotor changes in a patient presenting with a spontaneous semicircular horizontal canal plug. Patient: A 42-year-old man with acute spontaneous vertigo with spinning and persistent left-horizontal nystagmus, intensity but not direction dependent on head orientation with respect to gravity, indicating a benign paroxysmal positional vertigo due to otoconia causing a plug in the horizontal semicircular canal. Intervention: Electrophysiological and video-oculographic testing; vestibular rehabilitation. Main Outcome Measures: Cervical and ocular vestibular evoked myogenic potentials (VEMPs); video head impulse testing. Results: The video head-impulse test revealed an eye velocity cutoff at 80 degrees/s in the time interval from 40 to 90 ms after initiation of head impulses to the right. This normalized within 2 days after liberatory maneuvers, documenting for the first time a reversible deficiency of the cupular-endolymph high-frequency system dynamics. Cervical and ocular vestibular myogenic potentials were absent during stimulation of the affected side before the liberatory maneuvers but normalized within 30 to 80 days. Conclusion: This case is special in 4 respects: 1) nystagmus intensity, but not direction, was dependent on head orientation with respect to gravity, indicating a horizontal canal plug; 2) VEMPs were asymmetrical before liberatory maneuvers; 3) VEMPs recovered after Day 30; and 4) video head-impulse test asymmetry recovered. These observations challenge the common belief that VEMPs are evoked by otolith stimulation only. Instead, the assumption of a reversible canal dysfunction by a plug offers a more plausible explanation for all effects

Antidromic vs orthodromic sensory median nerve conduction studies

Objective: Median sensory nerve conduction studies are arguably the most often performed electrodiagnostic tests worldwide. Routine tests in clinical practice are done using either antidromic or orthodromic techniques type of stimulation, with no universal agreement on the use of one or the other technique. Methods: We review the advantages and drawbacks of antidromic and orthodromic as well as their particularities for clinical application and research. Results: The two techniques differ on how physical and physiological changes affect the action potential. Near-nerve recording is better suited for the orthodromic than for the antidromic technique, while studies of nerve excitability are better suited for the antidromic than for the orthodromic technique. Conclusion: Both techniques are equally suitable for routine tests but research studies may specifically demand one or the other. Keywords: Sensory nerve action potential, Antidromic nerve conduction test, Orthodromic nerve conduction test, Carpal tunnel syndrom

Unilateral reaction time task is delayed during contralateral movements

Performing unlearned unimanual tasks when simultaneously carrying out another task with the contralateral hand is known to be difficult. The dual task interference theory predicts that reaction time will be delayed if the investigated task is performed in the course of ongoing contralateral movements. Ballistic movements can be performed at maximal speed in simple reaction time (SRT) experiments when subjects have adequately prepared the motor system needed for movement execution. When fully prepared, activation of subcortical motor pathways by a startling auditory stimulus (SAS) triggers the whole reaction. In this study, we have examined dual task interference with reaction time in eight healthy volunteers. They were presented with a visual imperative signal to perform unilateral SRT either in a baseline condition (control trials) or while carrying out contralateral rhythmic oscillatory movements (test trials). A SAS was introduced in 25% of the trials in both conditions. SRT was significantly delayed in the interference test trial when compared to control trials either with or without SAS (P <0.001). Control and test trials with SAS were significantly faster than those without SAS in both conditions (P <0.001). However, there were no significant differences in the percentage SRT shortening induced by SAS or in the percentage SRT delay observed in the test trials. Our results suggest that performing rhythmic oscillatory movements with one limb slows SRT in the contralateral limb and that this effect is likely related to motor preparation changes. The effect described here can be of interest for physiological studies of interlimb coordination and the mechanisms underlying the dual task interference phenomenon

Prepulse inhibition of the blink reflex by laser stimuli in normal humans

The subcortical integrative effects of laser-induced activation of pain ascending tracts were examined in 11 healthy volunteers, aged 22-52 years. Subjects underwent either CO2 laser stimulation at the dorsum of the hand, electrical stimulation of digital nerves at the 3rd finger, or mechanical taps to the first dorsal interosseous space, preceding a blink reflex elicited by a supraorbital nerve electrical stimulus. The percentage inhibition induced in the R2 response of the blink reflex was similar for the three different stimulus modalities, but occurred at a different time interval. Compared to control trials, the R2 response of the test trials was a mean of 23.1% at the interval of 250 ms with laser stimuli, 17.4% at the interval of 100 ms with electrical stimuli to the 3rd finger, and 20.6% at the interval of 90 ms with a mechanical tap to the Ist interosseous space. Activation of pain receptors induce prepulse inhibition of the blink reflex at a delay corresponding to a slowly conducting pathway. The percentage inhibition is similar to that observed with other somatosensory inputs. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved

Evidence of neurophysiological improvement of early manifestations of small-fiber dysfunction after liver transplantation in a patient with familial amyloid neuropathy

Introduction: Small fiber polyneuropathy (SFP) is a common heralding clinical manifestation of damage to the nervous system in patients with familial amyloidosis. The diagnosis of SFP is a significant factor in the decision to treat a previously asymptomatic gene carrier, as treatment would prevent irreversible nerve damage. This requires detection of the earliest but unequivocal signs of peripheral nerve involvement. Case report: We present the case of a young female who was diagnosed of SFP, supported by data from quantitative sensory testing. She had preserved sensory nerve action potentials in the distalmost nerves of her feet and recordable nociceptive evoked potentials. She was successfully transplanted the liver from a previously healthy donor, and recovered fully of her symptoms and signs. Improvement was documented with repeated psychophysical and electrodiagnostic testing in the course of 4 years after transplantation. Significance: This case illustrates the utility of psychophysical testing to support the diagnosis of SFP. Keywords: Small fiber polyneuropathy, Familial amyloidosis, Quantitative sensory testing, Nociceptive evoked potentials, Psychophysical testing, Liver transplantatio