Integrative action of axonal membrane explored by trains of subthreshold stimuli applied to the peripheral nerve.

OBJECTIVE: The objective of this study was to provide evidence on the integrative action of axonal membrane in humans and its ability to integrate multipulse subthreshold stimuli and generate action potential. METHODS: The median nerve was stimulated at the wrist in six healthy subjects and 17 patients who underwent low spine surgery by means of percutaneous electrodes, with trains of one to nine near-threshold constant-current stimuli of 500-µs duration. The interstimulus interval between stimuli was 2 or 4 ms. The compound muscle action potential (CMAP) was recorded from the abductor pollicis brevis muscle using subcutaneous needle electrodes in patients and surface electrodes in healthy subjects. Total intravenous anesthesia (TIVA) without a muscle relaxant was used in all patients, and measurements were performed at the end of surgery. RESULT: A single near-threshold stimulus did not generate CMAP either in the healthy subjects or in the patients. However, when the number of near-threshold stimuli was increased to two to nine stimuli, and packed into a short train with interstimulus intervals of 2 or 4 ms, a CMAP of varying amplitude from 100 to 200 µV was successfully elicited. CONCLUSION: We concluded that the described phenomenon might be explained by the integrative action of the axonal membrane, which is able to summate the trains of subthreshold stimuli, increasing the resting potential to the firing level, and consequently generating CMAP. This is because the subthreshold stimuli make the axonal membrane hyperexcitable. SIGNIFICANCE: This phenomenon is not very well explored in clinical neurophysiology, and it needs to be studied further. This can explain some neurophysiologic phenomena during intraoperative monitoring.

[Narcolepsy: update on etiology, clinical features and treatment]. / Narcolepsia: actualización en etiología, manifestaciones clínicas y tratamiento.

Narcolepsy is a disease that involves an alteration in the generation and organisation of sleep. The main symptoms are excessive daytime sleepiness and cataplexy, followed by hypnagogic hallucinations, sleep paralysis and disrupted nocturnal sleep. The prevalence of typical narcolepsy oscillates between 25-50: 100.000 in general. Recently there has been a peak incidence in patients born in the month of March. According to the new classification, the Multiple Sleep Latency Test (MSLT) is mandatory for diagnosing narcolepsy without cataplexy, and advisable for diagnosing narcolepsy with cataplexy. Until now, the attempt has been made to control each symptom by its own specific treatment. At present, new American and European treatment guidelines propose new drugs that act on all the symptoms. The application of new criteria of diagnosis and treatment has improved the diagnosis, giving better options of treatment.

[Pseudo-conduction block in nonsystemic vasculitic neuropathy]. / Pseudobloqueo de conducción en vasculitis aislada del sistema nervioso periférico.

SUMMARY: Introduction. Nonsystemic vasculitic neuropathy (NSVN) is an inflammatory disorder of the vasa nervorum which usually is expressed as a mononeuritis multiplex. We present a patient with NSVN with histological confirmination focused on the neurophysiological findings at the early stages. CASE REPORT: A 36 years-old woman presented with paresthesia and weakness in her right hand followed by left footdrop. The first neurophysiologic examination showed low amplitude of the right median nerve (RMN) CMAP with proximal stimulation. A second examination showed signs of axonal damage in several nerves, including the RMN. CONCLUSIONS: The acute ischemic damage of a nerve can give a pattern of conduction block in the electroneurographic study as in the RMN of the presented case. This phenomenon is referred as "pseudo-conduction block", since it is transient and evolves towards a definite pattern of axonal neuropathy. When a vasculitic neuropathy is suspected, repeated neurophysiologic studies are necessary in order to ensure a proper (appropriate) characterization of the lesional patterns.

[Intraoperative neurophysiological monitoring: methods in neurosurgery]. / Monitorización neurofisiológica intraoperatoria: métodos en neurocirugía.

IONM uses different neurophysiological techniques during surgery time, thus avoiding possible lesions to the neurological structures, making surgery safer and better. We describe two types of IONM: mapping techniques and monitoring techniques, as well as their advantages, disadvantages and complications. We look into the more useful techniques in this field, as well as providing orientation about its use according to the surgical areas and the neurological structures under risk. In conclusion, we affirm that IONM is one of the most important advances in modern neurosurgery.

[Intraoperative neurophysiological monitoring in spine surgery]. / Monitorización neurofisiológica intraoperatoria en cirugía de columna.

Intraoperative neurophysiological monitoring (IONM) makes it possible to determine the status of neurological function during surgery. It guides the surgeon and minimises the risk of injury. This paper describes the different techniques available for IONM in spine surgery (somatosensory evoked potentials, motor evoked potentials, neurography, electromyography, reflexes and dermatomic evoked potentials), which neurophysiologists employ depending on the nerve structures at risk. In order for monitoring to be successful, coordination between all members of the surgical team is essential. In the event of IONM registering alterations, the neurophysiologist must first check the integrity of the recording system. The anaesthetist should then assess blood pressure, oxygen levels, ventilation and haematocrit values, and revert recent anaesthetic changes. Finally, the surgeon must stop the procedure and try to determine the cause of the event, and correct it if possible.

[Neurocysticercosis. An emergent disease]. / Neurocisticercosis. Una enfermedad emergente.

Neurocysticerosis is an affection of the central nervous system by the larvae of the Taenia solium. Although its diagnosis in our country is exceptional, in recent years a notable increase in the number of cases diagnosed has been observed, due to the phenomenon of immigration from countries where the disease is endemic. The most frequent form of presentation of neurocysticercosis is seizures, followed by headache. To diagnose it we must evaluate the epidemiological data, the clinical record and confirm this through neuroimage and immunological studies. The treatment selected should be pharmacological, principally with albendazole, and surgery reserved for cases where the former fails. Hygienic measures and the treatment of patients with teniasis are of great importance. Neurocysticerosis has ceased to be an exceptional diagnosis and given the foreseeable increase of its incidence in our milieu, health professionals must understand this disease and include it at higher levels of the algorithms of differential diagnosis.

[The pathophysiological basis of dystonia]. / Bases fisiopatológicas de la distonía.

OBJECTIVE: We review the mechanisms that may involved in the pathophysiology of dystonia. DEVELOPMENT: The role of basal ganglia, spinal and brainstem interneurons, and primary motor cortex in dystonia will be discussed. Abnormalities in the discharge pattern of internal pallidum or thalamus, secondary to basal ganglia disorders might be the cause of disbalance between excitatory and inhibitory mechanisms in motor cortex. Other factors such as excessive repetition of a movement or abnormal sensory afferent discharges may be participating in cortical reorganization. CONCLUSIONS: Overlapping of the cortical representation of dystonic muscles due to enlargement of cortical maps could explain overflow and co-contraction phenomena. The study of the exact role of these factors in each type of dystonia is a challenge for the future that opens the door for new therapeutic approaches.

[Clinical relevance of periodic limb movements during sleep in obstructive sleep apnea patients]. / Relevancia clínica de los movimientos periódicos de las piernas durante el sueño en pacientes con apneas obstructivas del sueño.

INTRODUCTION: The periodic limb movements disorder (PLMD) is frequently associated with the obstructive sleep apnea syndrome (OSAS), but the prevalence and clinical relevance of this association have not been studied in detail. OBJECTIVE: The objectives were to make a prospective study on the prevalence of PLMD in patients with OSAS, and correlate this association with clinical and respiratory parameters. PATIENTS AND METHODS: Forty-two patients diagnosed with OSAS, without clinical suspicion of PLMD, underwent a polysomnographic study. Clinical symptoms and signs were evaluated with an structured questionnaire, and respiratory parameters were obtained from the nocturnal study. RESULTS: Periodic limb movements were found in 10 patients (24%). There were no differences in clinical parameters between both groups (with and without periodical limb movements). However, respiratory parameters were significantly worse in patients without PLMD. CONCLUSIONS: PLMD is very frequent in patients with OSAS, and can contribute to worsen clinical signs and symptoms in these patients independently from respiratory parameters.

[Topographic distribution of visual evoked potentials in optic neuropathy]. / Distribución topográfica del potencial evocado visual en la neuropatía óptica.

INTRODUCTION: Digital treatment of electrical signals coming from the central nervous system on stimulation of the optic nerve path offers an objective method for evaluation of visual evoked potentials (VEP) shown graphically on a cerebral map. OBJECTIVE: To evaluate the topographical distribution of VEP in cases of optic neuropathy adding this parameter to the usual parameters of latency and amplitude. MATERIAL AND METHODS: We studied 35 patients with suspected optic neuropathy and normal findings on basic ophthalmological examination, in whom VEP and VEP mapping (VEPM) was done. RESULTS: In 26% of the cases there was no response for evaluation with the usual VEP recording techniques, whilst in those with VEPM this percentage was reduced to 11.5%. In the other cases there was a potential with characteristic distribution in the occipital areas and a maximally positive dipole posteriorly. CONCLUSION: VEPM is an objective method for evaluation of the visual pathway offering better discrimination than the usual VEP in more severe cases of neuropathy.