Leslie J. Dorfman

Age‐related changes in peripheral and central nerve conduction in man

Somatosensory evoked potential (SEP) latencies, motor and sensory nerve conduction velocities (CVs), and F-wave latenies were measured in 15 elderly normal subjects (mean age 74.1 years), and the results were used to derive indirect estimates of spinal cord CVs. These measurements were compared to those from 15 younger normal adults (mean age 31.6 years), and the nerve conduction characteristics of all 30 subjects were analyzed with respect to age. Peripheral motor and sensory CVs slowed progressively, and the onset latencies of F-waves and SEPs increased gradually with advancing age. Spinal cord CVs showed little change until approximately age 60, and declined sharply thereafter. In addition, the latencies of F-waves and SEPs were positively associated with height. Human clinical and experimental studies utilizing SEP and F-wave measurements must allow for morphologic differences between individuals, and for the systematic changes which accompany normal aging.

Automatic Decomposition of the Clinical Electromyogram

We describe a new, automatic signal-processing method (ADEMG) for extracting motor-unit action potentials (MUAPs) from the electromyographic interference pattern for clinical diagnostic purposes. The method employs digital filtering to select the spike components of the MUAPs from the background activity, identifies the spikes by template matching, averages the MUAP waveforms from the raw signal using the identified spikes as triggers, and measures their amplitudes, durations, rise rates, numbers of phases, and firing rates. Efficient new algorithms are used to align and compare spikes and to eliminate interference from the MUAP averages. In a typical 10-s signal recorded from the biceps brachii muscle using a needle electrode during a 20 percent-maximal isometric contraction, the method identifies 8-15 simultaneously active MUAPs and detects 30-70 percent of their occurrences. The analysis time is 90 s on a PDP-11/34A.

High-Resolution Alignment of Sampled Waveforms

Waveforms are often sampled faster than the Nyquist rate to obtain desired temporal resolution, even though, theoretically, oversampling adds no information and should not be necessary. This paper shows how high resolution can be achieved efficiently from data sampled at the Nyquist rate by working with coefficients of the Fourier-series expansion of the continuous interpolating waveform. Practical algorithms are presented for aligning and comparing waveforms, locating peaks, resolving superimpositions, and averaging overlapping waveforms. The algorithms prove to be more accurate, and to require fewer computations and less storage than techniques which employ continuous oversampling in many signal-processing applications, particularly template matching.

Leber's disease and dystonia A mitochondrial disease

We studied a kindred in which 8 members had the neuroretinopathy of Lebers disease; 14 had a progressive, generalized dystonia attributed to striatal degeneration; and 1 had both disorders. The mode of inheritance was compatible with maternal transmission. This neurologic disorder may be a mitochondrial disease.

On the Nature and Elimination of Stimulus Artifact in Nerve Signals Evoked and Recorded Using Surface Electrodes

The electrical stimulus pulse and the surface electrodes commonly used to study compound action potentials of peripheral nerves give rise to an artifact consisting of an initial spike and a longer lasting tail which often interferes with the recorded signal. The artifact has four sources: 1) the voltage gradient between the recording electordes caused by stimulus current flowing through the limb, 2) the common-mode voltage of the limb caused by current escaping through the ground electrode, 3) the capacitive coupling between the stimulating and recording leads, and 4) the high-pass filtering characteristics of the recording amplifier. This paper models these sources and presents several methodological rules for minimizing their effects. Also presented are three computer-based methods for subtracting the residual artifact from contaminated records using estimates of the artifact obtained from: 1) subthreshold stimulation, 2) a second recording site remote from the nerve, or 3) stimulation during the refractory period of the nerve.

Cytomegalovirus encephalitis in adults

l t i i i i ian infection with a cytoniegalovirus ((’MV) iii;iy he clinicaily inapparent or may pt.odiice o i i c o f several cyndroines ranging from ;i hc.nign. inorionucleosislike illiiess to ;L potentially I c t h a l disseiniiiiited disease. ‘those a t greatest risk include neonates: adults with dehilitaLinp diseases, particularly riidlignancics; a 11 d t h o s e 1ec e iv 1 ng I o ti gter ni i ni r n u n osu p prcsw r i t 0 1 \ teroid hortiione therapy. R e ~ t i t advat1cc.s 111 ! l i e t echn ics o f itiiiniiriology a n d diagnos t ic virology have increased o u r i i niters t ;I iiding ,if thr: Iiiologic behavior o f these viruses, but inticli rcruains t o hc learned ahou t their pathogenetic puten tial. ( ‘u r r en t investigations are :ittcnipting t o define routes of transmission, poshihlc str-ain differences i n virulence, ‘ind the signific:irice o f h o s t irnniunologic responses to infrctiori. particularly ;is these responses relate t o the concept of la tent infection.’ I n t h e fctiis and t iconate, generalixed (IMV infectioli often gives rise to iii:i.ior lesions in the i ie rvo~is system. which have tieen well descri1~c.d.L.css at ten tion h a s been directed to t h e ctwtral nervous sq’sterii ( ( ’ N S ) lesions in ~ d u l t s . 13artly bccause the iesjoris ai-e less extcnyivc than thc isc in i n f a n t s and also because disseniitiutrd (‘MV disease was rare in adults hcfore thc era of cancer chemotherapy and orgxn Irarisi,l3i~tntictn. In 1 he only studies w n ccriicci pi i inar i ly with the ncuropathologic fe;ttiires of ~it lu l t C’MV disease, Schnecks and Bailey ‘itid associutes6 have tlcscriheil a glialn d u l e encephalitis in renal transplant recipicsnts w h o had histologic evidence of C‘MV infection in other organs. Additional, less cons tant pithologic findings included I-od cell ( mi crl>giiaii as t iv: t t ion and prominent A L heiiner t y p e 11 astrocytes. Intracellular in3 4

AAEM minimonograph #47: Normative data in electrodiagnostic medicine

This article reviews, without mathematics, the important principles governing the acquisition and use of normative data in electrodiagnostic medicine. Common flaws in neurophysiological normative data include vague clinical criteria for establishing freedom from disease, samples that are too small and inadequately stratified, and application of Gaussian statistics to non‐Gaussian variables. Other problematic issues concern the trade‐off between permissible false‐positivity and false‐negativity in defining the limits of normative from sample data, test‐retest variability, and the use of multiple independent test measurements in each electrodiagnostic examination. The following standards for normative data are proposed: (1) standardized objective determination of freedom from disease; (2) appropriately large sample of normal subjects; (3) proportional statification of normal subjects for known relevant variables; (4) test of Gaussian fit for application of Gaussian statistics; and (5) data presentation by percentiles when Gaussian fit is in doubt. Many existing normative studies in clinical neurophysiology do not meet these standards. High‐quality normative data, readily accessible, is essential for the accurate electrodiagnosis of neuromuscular diseases.

Nerve fiber conduction-velocity distributions. I. Estimation based on the single-fiber and compound action potentials

A method is described for estimating the distribution of nerve-fiber conduction velocities in a nerve bundle. This method is based on a detailed general model of the nerve bundle compound action potential, which is characterized as a weighted sum of delayed single-fiber action potentials. The non-iterative estimation method is applied to two examples taken from existing literature, demonstrating the similarity of conduction velocity and fiber diameter distributions, sensitivity of the estimate to variations in important model parameters, and applicability to the differentiation of normal and abnormal nerve function.

Nerve fiber conduction-velocity distributions. II. Estimation based on two compound action potentials.

A method is presented for estimating nerve fiber conduction velocity distributions from non-invasive measurements of the compound action potential at two distinct locations separated by a known distance along the nerve bundle. This method is based on a model of the compound action potential as a weighted sum of delayed single-fiber action potentials, but does not require explicit knowledge of the single-fiber action potential wave shapes in order to yield a unique estimate of the conduction velocity distribution. Illustrative examples are presented from normal and diseases nerves. This method appears to have clinical applications in the electrophysiological assessment of peripheral nerve function.

Indirect estimation of spinal cord conduction velocity in man.

A method is described for deriving an indirect estimate of the velocity of impulse propagation in the spinal cord of intact man. The estimate is computed from measurements of motor and sensory nerve conduction velocity in the limbs, F-wave latencies, and the latencies of somatosensory evoked potentials. The mean estimated spinal cord conduction velocicy in normal subjects was found to be 55.1 m/sec, with a standard deviation of 9.9. This method appears to have potential application in the electrophysiological evaluation of patients with myelopathic disorders.