We investigated corticobulbar tract function by recording from the tongue and orofacial muscles and using transcranial magnetic stimulation (TMS) in 30 patients with amyotrophic lateral sclerosis (ALS) in order to improve the diagnostic yield in the detection of subclinical upper motor neuron (UMN) dysfunction. A UMN lesion was assumed when the peripheral conduction time and amplitude of the M-wave were within normal range and either the response to cortical stimulation was absent, or the central conduction time was delayed (> mean + 2.5 SD). Only two patients showed clinical evidence of UMN involvement in the cranial nerves, while TMS demonstrated corticobulbar tract dysfunction in the orofacial muscles in 17 patients (57%) and to the tongue in 15 patients (50%). Following recording at both sites, corticobulbar tract dysfunction was confirmed in 21 patients (70%). Twelve out of 13 patients with bulbar symptoms had evidence of additional subclinical corticobulbar tract involvement using TMS. In seven out of 15 patients with isolated limb involvement, subclinical corticobulbar tract dysfunction was demonstrated. Our results indicate the presence of early and, in most cases, subclinical corticobulbar tract involvement in the pathways to the orofacial muscles and tongue in ALS.

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In six healthy volunteers, the size of the motor unit action potential (MUAP) was related to its contractile behaviour. Electrical activity was determined by measuring amplitude and area of the potential, using the macro electromyography (EMG) technique. The mechanical response was characterised by contraction time, twitch force and relaxation time, recorded with the spike triggered averaging technique. With increasing tension of the whole muscle corresponding to an increasing threshold, the force of single units enlarged exponentially compared to their EMG. There was only a weak relationship between contraction time and electrical activity and none between EMG and relaxation time.

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The objective was to measure muscle fibre conduction velocity (MFCV) in the biceps brachii of normal subjects, and patients with mild myopathies and anterior horn cell diseases. Unisolated steel needles served as stimulation and recording electrodes. By aid of a computer program for data acquisition and analysis, up to 1,400 single fibre potentials could be recorded from a single muscle and analysed within 30-45 min. Normal values for mean, minimum, maximum CV and 5%, 25%, 75% and 95% percentiles were established. Females have slower mean and minimal CV than men but maximal MFCV were similar for the two groups. Age has no statistical influence. Myopathic patients showed a MFCV decrease of the already slow muscle fibre population. In neurogenetic diseases the distribution was biphasic with the conduction of the formerly fast conducting fibres either enhanced or reduced. Using different statistical parameters to describe the spectrum of muscle fibre conduction properties provides a sensitive tool to evaluate functional impairment in mild myopathies and to separate them from mild neuropathies.