Normative reference values for the dorsal sural nerve derived from a large multicenter cohort.

OBJECTIVES: Dorsal sural nerve conduction studies (NCS) may increase the sensitivity for the diagnosis of polyneuropathy, but clinical use is limited by a lack of reliable normative reference values in all age-groups. The aim of our study was to develop reference values for the dorsal sural nerve, based on a large multicenter cohort of healthy subjects. METHODS: Bilateral antidromic NCS were performed using standard surface electrodes in 229 healthy subjects (aged 21-80 years; median: 54 years). We assessed the normality of data distribution for amplitudes and conduction velocity (CV) and for their logarithmic (ln) transformation. The effects of age and height were determined using linear regression analysis. RESULTS: Sensory potentials were present in all subjects. Logarithmically transformed data were normally distributed. Age2 and height were most significantly associated with amplitude, and age and height with CV, respectively. There was no significant side-difference. Mean amplitudes (right and left) were 4.8 and 4.9 µV and mean CV 46.7 and 46.9 m/s. Reference limits were e (3.712515 - 0.0000956 * age2 - 0.0115883 * height ±â€¯1.96 * 0.51137) for amplitude and e (4.354374 - 0.0021081 * age - 0.0023354 * height ±â€¯1.96 * 0.11161) for CV. CONCLUSIONS: Dorsal sural nerve NCS are robust and have well defined normative limits. SIGNIFICANCE: The findings provide a basis for more sensitive NCS in clinical practice and future studies of the diagnostic accuracy of NCS in polyneuropathy.

Standardized computer-based organized reporting of EEG: SCORE.

The electroencephalography (EEG) signal has a high complexity, and the process of extracting clinically relevant features is achieved by visual analysis of the recordings. The interobserver agreement in EEG interpretation is only moderate. This is partly due to the method of reporting the findings in free-text format. The purpose of our endeavor was to create a computer-based system for EEG assessment and reporting, where the physicians would construct the reports by choosing from predefined elements for each relevant EEG feature, as well as the clinical phenomena (for video-EEG recordings). A working group of EEG experts took part in consensus workshops in Dianalund, Denmark, in 2010 and 2011. The faculty was approved by the Commission on European Affairs of the International League Against Epilepsy (ILAE). The working group produced a consensus proposal that went through a pan-European review process, organized by the European Chapter of the International Federation of Clinical Neurophysiology. The Standardised Computer-based Organised Reporting of EEG (SCORE) software was constructed based on the terms and features of the consensus statement and it was tested in the clinical practice. The main elements of SCORE are the following: personal data of the patient, referral data, recording conditions, modulators, background activity, drowsiness and sleep, interictal findings, "episodes" (clinical or subclinical events), physiologic patterns, patterns of uncertain significance, artifacts, polygraphic channels, and diagnostic significance. The following specific aspects of the neonatal EEGs are scored: alertness, temporal organization, and spatial organization. For each EEG finding, relevant features are scored using predefined terms. Definitions are provided for all EEG terms and features. SCORE can potentially improve the quality of EEG assessment and reporting; it will help incorporate the results of computer-assisted analysis into the report, it will make possible the build-up of a multinational database, and it will help in training young neurophysiologists.

Multiple mononeuropathy following cocaine abuse.

A 31-year-old man with acute-onset of left-sided weakness following the sniffing of cocaine was admitted with rhabdomyolysis. Neurophysiological studies showed axonal degeneration in 4/10 sensory and 3/8 motor nerves, and conduction block outside the typical compression-sites in 3/8 motor nerves. The findings are consistent with a diagnosis of multiple mononeuropathy. Ischaemia due to vasoconstriction is currently believed to be the cause of muscle necrosis following cocaine abuse and we hypothesise that it also explains the neuropathy in this case.

Nerve excitability changes in chronic renal failure indicate membrane depolarization due to hyperkalaemia.

Multiple nerve excitability measurements were used to investigate axonal membrane properties in patients with chronic renal failure (CRF). Nine patients were studied during routine haemodialysis therapy. The median nerve was stimulated at the wrist and compound muscle action potentials recorded from abductor pollicis brevis. Stimulus-response behaviour, strength-duration time constant, threshold electrotonus, current-threshold relationship and recovery cycle (refractoriness, superexcitability and late subexcitability) were recorded using a recently described protocol. In six patients, sequential studies were performed before, during and after haemodialysis. All patients underwent standard electrolyte and renal function tests before and after haemodialysis. Before dialysis, there were significant abnormalities in axonal excitability: reduced superexcitability; increased accommodation to depolarizing and hyperpolarizing currents; and a steeper current-threshold relationship compared with normal controls. These excitability parameters are the most sensitive to membrane potential and the abnormalities, which were all reduced by haemodialysis, closely resembled those in normal axons depolarized by ischaemia. Before dialysis, the excitability parameters correlated significantly with serum potassium (range 4.3-6.1 mM), but not with other markers of renal dysfunction: patients with normal axonal resting potentials had normal serum potassium, although urea and creatinine were elevated. We conclude that nerves are depolarized in many CRF patients and that the depolarization is primarily due to hyperkalaemia.