The reliability of commonly used electrophysiology measures.

BACKGROUND: Electrophysiological measures can help understand brain function both in healthy individuals and in the context of a disease. Given the amount of information that can be extracted from these measures and their frequent use, it is essential to know more about their inherent reliability. OBJECTIVE/HYPOTHESIS: To understand the reliability of electrophysiology measures in healthy individuals. We hypothesized that measures of threshold and latency would be the most reliable and least susceptible to methodological differences between study sites. METHODS: Somatosensory evoked potentials from 112 control participants; long-latency reflexes, transcranial magnetic stimulation with resting and active motor thresholds, motor evoked potential latencies, input/output curves, and short-latency sensory afferent inhibition and facilitation from 84 controls were collected at 3 visits over 24 months at 4 Track-On HD study sites. Reliability was assessed using intra-class correlation coefficients for absolute agreement, and the effects of reliability on statistical power are demonstrated for different sample sizes and study designs. RESULTS: Measures quantifying latencies, thresholds, and evoked responses at high stimulator intensities had the highest reliability, and required the smallest sample sizes to adequately power a study. Very few between-site differences were detected. CONCLUSIONS: Reliability and susceptibility to between-site differences should be evaluated for electrophysiological measures before including them in study designs. Levels of reliability vary substantially across electrophysiological measures, though there are few between-site differences. To address this, reliability should be used in conjunction with theoretical calculations to inform sample size and ensure studies are adequately powered to detect true change in measures of interest.

Transorbital sonography in acute optic neuritis: a case-control study.

BACKGROUND AND PURPOSE: Acute unilateral optic neuritis is associated with a thickening of the retrobulbar portion of the optic nerve as revealed by transorbital sonography, but no comparison has been made between nerve sheath diameter and optic nerve diameter in patients with acute optic neuritis versus healthy controls. We evaluated optic nerve sheath diameter and optic nerve diameter in patients with acute optic neuritis and healthy controls and compared optic nerve sheath diameter and optic nerve diameter with visual-evoked potentials in patients. MATERIALS AND METHODS: A case-control study was performed in 2 centers. Twenty-one consecutive patients with onset of visual loss during the prior 10 days and established acute noncompressive unilateral optic neuritis were compared with 21 healthy controls, matched for sex and age (±5 years). Two experienced vascular sonographers performed the study by using B-mode transorbital sonography. Visual-evoked potentials were performed on the same day as the transorbital sonography and were evaluated by an expert neurophysiologist. Sonographers and the neurophysiologist were blinded to the status of the patient or control and to clinical information, including the side of the affected eye. RESULTS: The median optic nerve sheath diameter was thicker on the affected side (6.3 mm; interquartile range, 5.9-7.2 mm) compared with the nonaffected side (5.5 mm; interquartile range, 5.1-6.2 mm; P < .0001) and controls (5.2 mm; interquartile range, 4.8-5.5 mm; P < .0001). The median optic nerve diameter was 3.0 mm (range, 2.8-3.1 mm) on the affected side and 2.9 mm (range, 2.8-3.1 mm) on the nonaffected side (P = not significant.). Both sides were thicker than those in controls (2.7 mm; interquartile range, 2.5-2.8 mm; P = .001 and .009). No correlation was found between optic nerve sheath diameter and optic nerve diameter and amplitude and latency of visual-evoked potentials in patients with optic neuritis. CONCLUSIONS: Transorbital sonography is a promising tool to support the clinical diagnosis of acute optic neuritis. Further studies are needed to define its specific role in the diagnosis and follow-up of optic neuritis.

Domain-specific suppression of auditory mismatch negativity with transcranial direct current stimulation.

OBJECTIVE: To evaluate the influence of frontal transcranial direct current stimulation (tDCS) on auditory mismatch negativity (MMN). METHODS: MMN is an event related potential calculated by subtracting the amplitude of the evoked potentials in response to a "standard" stimulus from the evoked potentials produced by a rare "oddball" stimulus. Here we assessed the influence of anodal tDCS, cathodal tDCS or sham stimulation delivered over the right inferior frontal cortex on MMN in response to duration and frequency auditory deviants in 10 healthy subjects. RESULTS: MMN to frequency deviants was significantly reduced after anodal tDCS compared with sham or cathodal stimulation which did not change MMN to frequency deviants. Neither anodal nor cathodal tDCS had any effect on MMN to duration deviants. CONCLUSIONS: Non-invasive brain stimulation with tDCS can influence MMN. The differing networks known to be activated by duration and frequency deviants could account for the differential effect of tDCS on duration and frequency MMN. SIGNIFICANCE: Non-invasive brain stimulation could be a useful method to manipulate MMN for experimental purposes.

Intermittent photic stimulation affects motor cortex excitability in photosensitive idiopathic generalized epilepsy.

PURPOSE: To assess the effect of intermittent photic stimulation (IPS) at a common activating frequency, i.e. 20Hz, on motor cortex excitability by means of transcranial magnetic stimulation (TMS) in photosensitive patients with idiopathic generalized epilepsy (IGE). METHODS: We studied 15 photosensitive IGE patients showing a photoparoxysmal response (PPR) to IPS at 20Hz. Nineteen normal subjects of similar age and sex acted as controls. After the resting motor threshold (rMT) was measured, we studied the corticomotor excitability in two conditions randomly delivered, during IPS (5s) at 20Hz and without IPS. Motor evoked potentials (MEPs) were recorded from the right first dorsal interosseous muscle (FDI). We determined the cortical silent period (cSP), the short-latency intracortical inhibition (SICI) at the interstimulus interval (ISI) of 3 and 4ms and the intracortical facilitation (ICF) at ISIs of 12 and 14ms. Data were analyzed by means of rmANOVAs. RESULTS: IPS at 20Hz is significantly shortening the cSP in normal subjects, while no significant changes were detected in patients. The rMT was significantly higher in patients than controls, as expected by the concurrent antiepileptic treatment. Other corticomotor excitability measures were unaffected. CONCLUSIONS: We confirm that IPS has a weak influence on the motor cortical output in patients with IGE and PPR. The loss of the normal shortening of the cSP, otherwise present in healthy subjects in response to IPS, may have a possible protective nature.

Health-related quality of life measures and psychiatric comorbidity in patients with migraine.

BACKGROUND AND PURPOSE: The identification of factors associated to health-related quality of life (HRQoL) measures in patients with migraine has major implications in terms of prognosis and treatment. This study aimed at investigating associations between HRQoL and comorbid mood and anxiety disorders. METHODS: Consecutive adult outpatients with a diagnosis of migraine with or without aura were assessed using the Mini International Neuropsychiatric Interview (M.I.N.I.) Plus version 5.0.0 and the Migraine-Specific Quality-of-Life Questionnaire (MSQ). RESULTS: Data of 112 patients (82 females), 69 without aura, mean age 41.2 +/- 13.3 years were analyzed. According to the M.I.N.I., 50% patients had a lifetime or current DSM-IV diagnosis of mood or anxiety disorder. There was no between-groups difference in MSQ total and subscale scores in relation to the presence/absence of psychiatric comorbidity, independently whether that was current or lifetime. In the group of subjects with psychiatric disorders, age at onset of migraine correlated with MSQ-total (rho = -0.407 P = 0.002), and subscale scores (Role Function-Restrictive, rho = -0.397, P = 0.002; Emotional Function, rho = -0.487, P < 0.001). CONCLUSIONS: Our findings suggest that current and/or lifetime psychiatric comorbidities are not associated with HRQoL measures in patients with migraine. However, patients with migraine and psychiatric comorbidities may represent a specific subgroup deserving particular attention for targeted interventions.

Measuring the level and content of consciousness during epileptic seizures: the Ictal Consciousness Inventory.

Ictal alterations of the level of general awareness and subjective content of consciousness play a pivotal role in the clinical phenomenology of epilepsy, and reflect the pathological involvement of different neurobiological substrates. However, no self-reported measures have been proposed for patients experiencing altered conscious states during seizures. This study describes the development and validation of a new scale for the quantitative assessment of the level and content of ictal consciousness, the Ictal Consciousness Inventory (ICI). The ICI is a 20-item questionnaire generated on the basis of interviews with patients, literature review, and consultation with experts. It was tested on a sample of 110 patients attending three different epilepsy clinics in Northern Italy, who also completed standardized clinical scales. Standard psychometric methods were used to demonstrate that this scale satisfies criteria for acceptability, reliability, and validity. The ICI is proposed as a user-friendly and clinically sound instrument for the measurement of ictal alterations of consciousness in patients with epilepsy.