Immunoglobulin treatment versus plasma exchange in patients with chronic moderate to severe myasthenia gravis.

The purpose of this study was to compare the efficacy of high-dose intravenous immunoglobulin (IVIG) treatment with plasma exchange in patients suffering from moderate to severe myasthenia gravis (MG) in a stable phase. There are no controlled studies comparing IVIG with plasma exchange in patients who despite immunosuppressive treatment have persistent incapacitating MG symptoms. This was a controlled crossover study. Twelve patients with generalized moderate to severe MG on immunosuppressive treatment for at least 12 months were included. The patients were evaluated clinically using a quantified MG clinical score (QMGS) before and at follow-up visits after each treatment. One week after the treatments, the patients who received plasma exchange treatment showed a significant improvement in QMGS compared to baseline but although some improvement was seen after IVIG this did not reach statistical significance. Four weeks after both plasma exchange and IVIG treatments, there was a significant improvement in QMGS compared to baseline. One week and 4 weeks after treatment, no significant difference between the 2 treatments was found. Both treatments have a clinically significant effect 4 weeks out in patients with chronic MG, but the improvement has a more rapid onset after plasma exchange than after IVIG.

KANDID--an EMG decision support system--evaluated in a European multicenter trial.

KANDID is an advanced EMG decision support system dedicated to the support of the clinical neurophysiologist during EMG examinations. It has facilities for test planning, automatized and structured data interpretation, EMG diagnosis, explanation, and reporting. In a prospective European multicenter field trial, the agreement levels between clinical neurophysiologists and KANDID's diagnostic statements were measured under ordinary clinical EMG practice. KANDID was assessed in 159 individual patient EMG examinations by nine clinical neurophysiologists at seven different EMG laboratories. The reasoning of KANDID was considered understandable for the examiners in 80-90% of cases. The agreement level for the electrophysiological states of muscles and nerves between KANDID and the individual examiners was, on average, 81%. The corresponding diagnostic agreement with KANDID was, on average, 61%. A pronounced interexaminer variation in the agreement level related to the different EMG centers was observed. All Danish and Belgian examiners agreed with KANDID in more than 50% of their cases with regard to the EMG diagnosis, while the English examiners were in agreement with KANDID in 50% or less of their cases. These differences were possibly due to differences in epidemiology, examination techniques, control material, and examination planning strategies. It is concluded that it is possible to transfer systems like KANDID out of their development sites and apply them successfully if they can be locally customized by the clinical end users via editors.

[Preoperative and postoperative magnetoencephalography in a patient with partial epilepsy]. / Prae-og postoperativ magnetoencefalografisk undersøgelse af en patient med partiel epilepsi.

Magnetoencephalography (MEG) is a non-invasive method with a potential of clinical diagnostic use to localize epileptogenic foci in the brain. The aim of this study was to investigate whether the pathological focus localized by MEG was concurrent with the conventional preoperative examinations in a patient with medically intractable epilepsy who underwent surgery (left side uncohippocampectomy). A conventional preoperative test battery had already documented a left-hemisphere fronto-temporal epileptogenic focus. Postoperatively the patient was seizure free. MEG was performed three months before and ten months after the operation. The analysis of the MEG data indicated a left hemisphere fronto-temporal focus in agreement with results obtained by means of the conventional methods used for locating epileptic foci. Postoperatively the focus had disappeared.

EMG power spectrum, turns-amplitude analysis and motor unit potential duration in neuromuscular disorders.

The diagnostic value of power spectrum analysis of the needle EMG pattern at a force of 30% of maximum was compared to that of turns-amplitude analysis and to that of manual measurements of motor unit potential (MUP) duration in the brachial biceps muscle of 20 patients with myopathy and 11 patients with neurogenic disorders. In myopathy the power spectrum analysis had the same diagnostic value as the turns-amplitude analysis and MUP duration measurements and the 3 methods supplemented each other. In patients with neurogenic disorders the diagnostic value of the power spectrum analysis as well as that of the turns-amplitude analysis were lesser than that of MUP duration measurement. In diseased muscles the amount of high frequencies increased with increasing ratio of turns to mean amplitude while there was no relation between the power spectrum and the MUP changes. The results suggest that the power spectrum analysis of EMG can be used as a diagnostic tool in patients with neuromuscular disorders.

Power spectrum analysis of the EMG pattern in normal and diseased muscles.

The diagnostic value of analogue frequency analysis of EMG from patients with neuromuscular disorders has not been convincing. Using fast Fourier transformation it is today possible to obtain the EMG power spectrum on-line and with a better resolution. We examined the power spectrum of the EMG pattern of the brachial biceps muscle in 20 control subjects, 20 patients with myopathy, and 12 with neurogenic disorders. The electrical activity was sampled with a concentric needle electrode from 10 sites in each muscle. From each spectrum, mean power frequency, the power at 140 Hz, 1400 Hz, 2800 Hz and 4200 Hz relative to total power and the high/low ratio (1400/140) were obtained. The mean power frequency was higher at 10% than at 30% of maximal force. At a force of 30% of maximum the power spectrum analysis identified 55% and 64% of the patients with myopathy and neurogenic disorders, respectively. Although the diagnostic yield of the power spectrum analysis at a force of 10% of maximum was less than that at 30%, additional patients were identified at 10% increasing the diagnostic yield to 65% and 73% for patients with myopathy and neurogenic disorders, respectively. The best diagnostic parameters were the mean power frequency and the relative power at 1400 Hz.

The motor unit firing rate and the power spectrum of EMG in humans.

The EMG power spectrum is influenced by many factors such as the conduction velocity of the muscle fiber, the action potential of the motor unit, the number of motor units firing near the electrode, and the recording conditions. Model studies of the relation between motor unit firing rate and power spectrum of EMG have produced conflicting results. To examine this relation in vivo the brachial biceps muscle was examined in 14 controls at a force of 10% of maximum. The motor unit firing intervals were obtained from 164 motor units, sampled with a single fiber electrode. The EMG was sampled at 10 sites in each muscle with a concentric electrode and the power spectrum was obtained using fast Fourier transformation. The mean power frequency of the interference pattern as well as the relative power at 1400 Hz both decreased with increasing motor unit firing intervals between subjects. The study thus indicates that the amount of high frequencies in the power spectrum is greater in a subject with a high firing rate of the motor units than in a subject with a low firing rate.