The role of occipital cortex hyperexcitability in visual snow syndrome
Isin Unal-Cevik DOI:10.4103/nsn.nsn_193_21
Visual snow syndrome (VSS) is an emerging clinical entity, mainly characterized by persistent, bilateral, whole-visual field, disturbing, small flickering dots or pixelation, floaters, palinopsia, nyctalopia, photopsia, and photophobia. Patients with VSS also describe associated symptoms such as tinnitus, concentration difficulty, lethargy, depression, anxiety, and irritability, all of which affect the patients' quality of life. The consistency of these visual and nonvisual symptoms has recently led to proposed criteria for VSS. The diagnosis relies on the exclusion of other ophthalmic or neuropsychiatric disorders. Interestingly, many patients may have a comorbid migraine, and the symptoms were previously attributed as a persistent visual phenomenon in migraine. VSS is listed in the International Classification of Headache Disorders-Third Edition Appendix as a complication of migraine; however, VSS is a new disease entity distinct from persistent migraine aura. Some patients with VSS recall exposure to illicit hallucinogenic drugs, amphetamines, cannabis, or Lysergic acid diethylamide (LSD). The stereotypic clinical characteristics of VSS are currently well defined, and the pathophysiology is under investigation. Due to the subjective perceptual descriptions of patients with VSS, objective electrophysiologic parameters and functional brain imaging studies using magnetic resonance imaging and positron emission tomography are warranted for defining the quantifiable and reliable outcome measures. Patients with migraine, idiopathic occipital epilepsies, patients with Alice in Wonderland syndrome, patients with Charles Bonnet syndrome, visual hallucinations in recovery from cortical blindness, and recreational 3,4-methylenedioxymethamphetamine/ecstasy users have been suggested to have occipital cortex hyperexcitability. VSS is attributed to involving a dysfunctional magnocellular pathway, thalamocortical dysrhythmia, dysfunctional central visual processing, and occipital cortex hyperexcitability as possible underlying mechanisms. This review will focus on the role of occipital cortex hyperexcitability in VSS and hopefully provide insight into its pathophysiology and therapeutic strategies.
Background: A single transcranial magnetic pulse over the motor cortex is known to generate repetitive descending activity along the corticospinal tract. With respect to the origin; the earliest volley is named direct wave and the subsequent activity forms indirect (I) waves. I waves are assumed to originate from corticocortical afferents; they can be modulated by several methods and are practical parameters for evaluating motor cortex excitability. Weak transcranial direct current stimulation (tDCS), which has been widely used in human studies since the early 2000s, is a noninvasive and painless modulatory method for studying cortical excitability. We aimed to investigate the modulatory effects of anodal and cathodal tDCS on I waves of healthy controls, as a component of the motor evoked potential response generator. MaterialsandMethods: Twelve healthy volunteers were enrolled in the study. One mA tDCS was applied for 10 min and; single motor unit (SMU) recording technique was used for the identification of I waves. Two conditions were analyzed for each SMU in both anodal and cathodal current polarities; before tDCS and after tDCS. Separate peristimulus time histograms were constituted for each condition. Total peak duration, early peak latency, early peak duration, and early peak discharge rate were calculated. Results: Total peak duration, early peak latency, and early peak duration did not differ between pre- and post-tDCS conditions in either polarity. However, I1 peak discharge rate was found to be significantly decreased after cathodal tDCS (P: 0.017) and increased after anodal tDCS (P: 0.003). Conclusion: Our results confirm polarity-specific effects of tDCS of the primary motor cortex on I waves. According to our knowledge, this is the first study evaluating modulatory effects of tDCS on I waves using SMU recording technique.
Why electrophysiological reassessment is needed? The experience of our laboratory – A cross-sectional study
Isil Yazici Gencdal, Ayşe Nur Özdağ Acarlı, Ayşe Deniz Elmalı, Ahmed Serkan Emekli, Ali Emre Öge, Mehmet Barış Baslo, Elif Kocasoy Orhan DOI:10.4103/nsn.nsn_233_21
Introduction: Requesting repetition of an electrodiagnostic examination (EDX) for follow-up and/or diagnostic verification is common in the daily practice of a reference center. Objective: This study aimed to evaluate demographical and electrophysiological characteristics of the patients who were referred to a reference electrophysiology laboratory for reassessment, to explore the underlying reasons, and motives for ordering a reassessment. Methods: Patients who had at least one EDX study within the last year in one of the two different time periods (winter and summer) were included in the study. Their demographical features, preliminary diagnosis, and electrophysiological findings were assessed and compared with their previous EDX interpretations. Results: Thirty-five (14 female, 21 male) patients (7,7%) out of 457 patients from the winter period (November 11, 2018‒December 12, 2018) and 38 (20 female, 18 male) patients (7,8%) out of 487 patients from the summer period (July 01, 2019‒August 08, 2019) were included in the study. Age, gender, preliminary diagnosis, and the number of previous electrophysiologic tests were statistically similar between the two groups. The most common reason for reassessment was to verify or to follow-up on a diagnosis of motor neuron disease or polyneuropathy. Compared to the summer group, the patients who had previous EDX in a different center were more common in the winter group, mean duration between EDX studies was also shorter. Conclusion: In this study, we have inspected the patients referred to our laboratory within two different time frames in a year for a repeat EDX study. It was observed that the number of patients who underwent a repeat EDX was relatively low, and there was no significant difference not only in the preliminary diagnosis but also in the electrophysiological findings.
Context: Restless legs syndrome (RLS) is a neurological sleep disorder which causes an overwhelming urge to move the legs. However, this spinal excitability can be decreased through the use some motor movements such as walking or stretching. Aims: This study aimed to investigate the effect of motor imagery (MI) on spinal excitability in relation to the H reflex (HR). Settings and Design: In this study, 11 patients diagnosed with RLS (3 males and 8 females, mean age: 41.2) and 14 controls (8 males and 7 females, mean age: 38.4) were tested. HR was studied while participants in the supine position were imagining walking and also while imagining both dorsiflexion (DF) and plantar flexion (PF). Results: There was significant decrease in the Hmax/Mmax at 90° DF in both groups (p = 0.002, p = 0.001). There was no significant decrease in the RLS group on imagery; however, there was a significant decrease in the control group with movement imagination compared to the resting state (p = 0.021). There was no significant increase in Hmax/Mmax at 135° PF in both groups on movement and imagery. There was a decrease in the ratio on the imagery of walking in the RLS group (p = 0.038), but the same ratio increased in the control group (p = 0.010). Conclusion: As motor movements decrease corticospinal excitability in RLS, the imagery of movement mimicking the actmovement can relieve the symptoms of RLS. As a conclusion, further electrophysiological studies can be useful to gauge the effects of MI on spinal excitability in RLS.
Objective: Nonconvulsive status epilepticus (NCSE) is a challenge to diagnose in some cases, and recently, Salzburg consensus criteria for NCSE (SCC-NCSE) were developed to contribute to clinical practice. We aimed to investigate their validity and usefulness by reevaluating the electroencephalogram (EEG) examinations of our patients in this study. Materials and Methods: We retrospectively evaluated all EEG recordings of patients diagnosed with NCSE by experienced clinical neurophysiologists in our EEG laboratory over a period of 2 years. Two neurologists trained in EEG reanalyzed all EEG data and categorized these patients as NCSE, possible NCSE, or non-NCSE using the SCC-NCSE. Results: Twenty-nine patients with a mean age of 31.5 ± 25.9 were reanalyzed. According to the SCC-NCSE, 24 patients (82.7%) were diagnosed as NCSE. Eighteen patients (62%) who fulfilled all SCC-NCSE were diagnosed as NCSE, whereas six patients (20.7%) were diagnosed only as possible NCSE. Five patients (17.3%) did not fulfill SCC-NCSE; the reasons are the lack of additional secondary criteria in 2 patients with encephalopathy, the absence of full compliance with the criteria in other 2 patients, and a diagnosis of electrical status epilepticus during sleep in the last patient. Conclusion: The results of our study show that SCC-NCSE is highly consistent with clinical practice to decide for the diagnosis of NCSE. The evaluation of NCSE according to a set of new standardized criteria is thought to be difficult in practice, but it provides a more objective assessment. Therefore, we believe that its use should be encouraged to increase experience and the possibility of correct diagnosis.