Prognostic value of cortical magnetic stimulation in spinal cord injury.

Cortical magnetic stimulation was performed in a consecutive series of 10 patients presenting within 15 days of traumatic spinal cord injury. In those patients with complete paraplegia or quadriplegia, motor evoked potentials at presentation were absent below the level of the lesion. Six months after the injury, potentials had returned in the biceps brachii and abductor pollicis brevis muscles in some quadriplegic cases, but remained absent from the tibialis anterior in all of this group. None of those with a complete lesion made a significant functional recovery. Of the three patients with incomplete quadriplegia, two showed a significant recovery after 6 months. Motor evoked potentials were recordable below the level of the lesion at presentation in these cases, although the latencies were prolonged. In the remaining patient who failed to improve, potentials were unrecordable throughout the study. This small pilot study suggests that cortical magnetic stimulation may be useful in refining the prognosis in patients with an incomplete spinal cord injury.

Accuracy, reproducibility, and variability of hand-held dynamometry in motor neuron disease.

A spring-loaded device that "breaks" at preset forces was used to assess readings obtained by hand-held dynamometry by three raters with varying experience in the method. Overall accuracy (3%), but not reproducibility or variability, was improved by greater experience. Readings obtained jointly by three raters had 53% greater variability than those obtained by a single rater. Nine muscle groups in 19 patients with motor neuron disease were assessed at 10 sessions (three replications per session) over six days by the experienced rater. Muscle force was expressed relative to that of 22 matched normal controls. The reproducibility was good with a mean % difference of 13.2 and repeatability coefficient of 2.17 kg-force for readings six days apart; the overall correlation coefficient was 0.98. The mean coefficient of variation (CV) of 10 readings was 9.9%. The poorer reproducibility and greater variability seen in clinically weaker muscles may account for differences in patients with bulbar palsy and classical amyotrophic lateral sclerosis; the degree of spasticity had no effect. The rater was estimated to contribute 37% of the total variability when testing patients. The use of a composite score by combining normalised dynamometry readings of eight limb muscles improved mean % difference to 6.7 and mean CV to 5.8%. The reproducibility and variability of hand-held dynamometry readings obtained by a single rater compare well with those of fixed devices. Readings from single raters, irrespective of experience, have similar reproducibility and variability. If, however, multiple raters are used in longitudinal assessments of individual patients, as occurs in clinical trials, the variability of their combined readings should be estimated when calculating the same size required.

Voluntary activation and fiber density of fasciculations in motor neuron disease.

Two hundred voluntarily activated motor units and 211 fasciculations were recorded in the biceps of 10 patients with motor neuron disease with the Macro EMG technique. Twenty-two fasciculations, in nine of 10 muscles, had a potential of closely similar shape, amplitude, and area to that of a voluntary unit. Fasciculating units that could not be activated voluntarily had a higher mean number of spikes in their triggering single fiber potentials than units that could only be activated voluntarily, but statistically similar Macro EMG parameters. The mean number of single fiber spikes, and Macro EMG parameters, of fasciculations activated voluntarily, were similar to those of units that were only activated voluntarily. A positive correlation between fiber density and Macro EMG median amplitude and area in individual patients, and between number of single fiber spikes and Macro EMG amplitudes and areas in the pooled data, was found for fasciculations but not for voluntary units. At least 10% of fasciculations in patients with motor neuron disease may originate near or above the point of axonal branching and a proportion of those without evidence of voluntary activation may have a higher number of smaller muscle fibers, or more closely packed muscle fibers, of similar or greater size, than voluntarily activated motor units. Differences in the peripheral microanatomy of a number of fasciculation units not activated voluntarily may underlie ectopic impulse generation in the terminal axonal arborization, endplate zone, or muscle fibers of these units.

Preferential generation of recurrent responses by groups of motor neurons in man. Conventional and single unit F wave studies.

Conventionally recorded surface F waves over the abductor digiti minimi muscle sampled a wide range of conduction velocities (CVs). Single motor unit (MU) F responses to threshold stimulation of the ulnar nerve were recorded with bipolar needle electrodes (BNE); the mean latencies of their fastest associated surface single unit M and F potentials were similar to those of the compound muscle action potential and fastest F wave, indicating that the fastest F wave indexes adequately the fastest motor fibre of the ulnar nerve. The mean surface unit F amplitude of MUs recorded by a BNE was similar to that of voluntary MUs recorded with a spike-triggered averaging technique; an estimated mean of 2-3 MUs per F wave was found by two methods. The frequency distribution of estimated F wave CVs was shifted towards faster values than expected from available studies of the distribution of CVs in single peripheral nerves; it was also higher than predicted from the expected relation between this distribution and the number of MUs per F wave, if an equal chance of activation and recording is assumed for each MU. There was a significant positive correlation between the frequency of F responses and their CV in 81 single MUs recorded by a BNE and tested with 200 threshold stimuli. These findings are consistent with preferential generation of recurrent responses by larger MUs; it may relate to a lesser chance of antidromic discharge in the smaller motor neurons and to a greater chance of collision of orthodromic (reflex) and antidromic impulses in their axons. The higher than expected percentage of all F waves that were repeater shapes or waves, and the presence of several distinct peaks in the distribution of intervals between repeaters of the same shape, suggest special, and heterogeneous, functional and anatomical arrangements in the groups of motor neurons generating them. Repeaters had greater amplitude and area, but similar latency and duration, than F wave shapes that did not repeat, suggesting that the former have a larger number of component MUs.

Comparative efficacy and safety of intravenous and oral administration of a TRH analogue (RX77368) in motor neuron disease.

Ten consecutive patients with motor neuron disease (MND) who had bulbar symptoms received one or two intravenous doses followed by increasing oral doses of a TRH analogue (RX77368). Similar improvements in speech, swallowing and in tongue and jaw movements were seen after iv and oral administration in nine, five and eight patients respectively. The initial time course of improvement correlated with increasing plasma levels of the drug, but most clinical effects persisted when the levels decreased and became undetectable after 24 hours. The oral solution was tasteless and had no, or minimal, side effects.

Subacute administration of a TRH analogue (RX77368) in motorneuron disease: an open study.

Sixteen patients with motor neuron disease received RX77368, a TRH analogue, IV, repeatedly over 1-12 weeks (median 2 weeks). Slight to moderate improvement in bulbar function, particularly speech, was reproduced or persisted with repeated infusions in 8 of 12 responders over a median of 18 days (range 14-90) during the period of study. Cramps (5/9) and spasticity (5/8) improved for a median of 14 days (range 7-35) and 7 days (range 2-14) respectively. The highest benefit/side effect ratio was seen with 0.2 mg/kg (0.15 mg/kg in those with severe bulbar palsy) every 3-4 days. Long term studies with this analogue in MND are indicated.

Short-term stability of single motor unit recordings in motor neuron disease: a macro EMG study.

Thirty five individual macro EMG motor unit potentials in 13 patients with motor neuron disease were recorded every 15 minutes during a 2 hour period. No significant change in amplitude or area was seen in 15 control units in nine patients or in 20 units in 11 patients receiving RX77368 0.2-0.3 mg/kg. The findings provide no evidence for an action of this long acting TRH analogue on the peripheral territory of motor units in motor neuron disease.