Giant repeater F-wave in patients with anterior horn cell disorders. Role of motor unit size.

Conventional F-wave responses as well as single motor unit F-wave responses together with the volitionally recruited motor unit action potentials (MUAP) were studied in hand and feet muscles of 10 healthy subjects and 32 patients with anterior horn cell disorders. The amplitude of the largest F-wave (Fl) was significantly greater in the affected patients compared with healthy subjects. Giant repeater F-wave responses "up to 4 mV" were recorded in muscles having volitionally recruited giant MUAPs. Although, the group mean percentage of motor unit F-wave responses per stimulation in all tested orthodromic MUAPs was significantly decreased in amyotrophic lateral sclerosis patients, the group mean percentage of motor unit F-wave responses per stimulation in all tested orthodromic MUAPs that gave motor unit F-wave response was significantly increased compared with healthy subjects. The responding orthodromic MUAP gave identical motor unit F-wave response, even for complex polyphasic units. Enhanced monosynaptic (H-) reflex, proximal axon reflex (A-wave), and repetitive muscle response as possible explanations for the giant F-wave responses could be discounted. The electrophysiologic behavior of the giant late responses described here fits well with the criteria of F-waves modulated by newly formed distal (and or proximal) axonal branching.

The origin of R2 of the blink reflex recorded on the affected side of patients with complete facial nerve paralysis.

The possible mechanisms contributing to the generation of R2-like response were investigated in 19 patients with complete facial nerve paralysis, where the efferent limb of the reflex arc is absent. The first possibility that potentials produced by the unaffected orbicularis oculi (0.0c) are conducted to the reference electrode taped over the nose was confirmed as the amplitude of R2 on the affected side was significantly reduced when the reference electrode was removed from the nose and taped on the ear lobule. The second possibility of volume conducted potentials produced by muscular generator in temporalis and masseter muscles through trigemino-trigeminal reflex was suggested in some patients based on three reproducible observations: (1) EMG activity of high amplitude could be recorded with electrodes taped over the affected 0.0c muscle during voluntary teeth clenching, (2) R2-like responses were recorded in patients with bilateral complete facial paralysis, (3) R2-like responses were recorded from temporalis and masseter muscles. The contribution of extraocular muscles could be discounted as R2 could be recorded from patients with Möbius's syndrome who had complete bilateral facio-ocular paralysis. The results of the present study further support the greater value of R1--rather than R2--in predicting clinical outcome of patients with peripheral facial nerve palsy.

Impaired afferent control in patients with spastic hemiplegia at different recovery stages: contribution to gait disorder.

The cerebral somatosensory potentials (SEP) evoked by electrical stimulation of the tibial nerve on the affected and unaffected limbs during stance and gait were recorded in 50 patients with spastic hemiplegia. On the unaffected side, the onset of the cortical activation during gait was 15 to 20ms later, and the amplitude was about 50% smaller than that recorded during stance condition. This was attributed to blocking of Ia afferent fibers during gait. SEPs recorded on the affected side during gait were, in general, of smaller amplitude and appeared with a shorter latency than in the unaffected side. During gait, 22 affected limbs showed a "Ia" blocking pattern of SEPs whereas another 28 showed a nonblocking pattern. The behavior of SEPs was analyzed with respect to three clinical identifiable recovery stages of voluntary movements in the spastic limbs (namely synergistic, isolated, and useful movements). The blocking pattern during gait was usually present in good functioning limbs, whereas the nonblocking pattern was usually present in poorly functioning limbs. It is concluded that the change in the gait pattern of hemiparetic patients represents a shift from good relevant functioning group II-afferent system to a predominance of functionally ineffective group I-afferent system.

Impaired activation pattern in antagonistic elbow muscles of patients with spastic hemiparesis: contribution to movement disorder.

Surface electromyographic "EMG" activity in biceps brachii (agonist muscle) and triceps brachii (antagonist muscle) as well as the discharge behaviour of motor units "MUs" (needle recording) in biceps brachii muscle were recorded during slow (0.33 Hz) and fast (0.66 Hz) voluntary elbow flexion movements (auditory matching task) in fifty patients with spastic hemiplegia. In the spastic limbs, a long lasting, small amplitude tonic co-contraction of antagonist muscles was seen during slow flexions (SF) in 29 cases. This effect was strongest during the fast elbow flexion movements (FF). In 33 patients a triphasic pattern of muscle activation was observed on the unaffected side but not on the spastic side. The amplitude of the agonist surface EMG was significantly reduced and the amplitudes of the MU potentials recruited during maximal effort were generally smaller on the spastic side compared to the unaffected side. The agonist-antagonist activation pattern was analysed with respect to three clinically identifiable functional recovery stages of voluntary movements in the spastic limbs, namely synergistic, isolated and useful movements. The MU amplitudes and the amplitude of the surface EMG activity in the agonist muscle recorded during FF movements became significantly larger whereas the amplitude of the antagonist tonic activity became smaller with increasing functional recovery of the limb. It is concluded that impaired recruitment of type II motor units in the agonist muscles and the inability to selectively activate the agonist muscle contribute to the deficit in motor performance in spastic paresis.

Patients with spastic hemiplegia at different recovery stages: evidence of reciprocal modulation of early/late reflex responses.

Reflex electromyographic (EMG) muscle responses were recorded from abductor pollicis brevis (APB) and tibialis anterior (TA) muscles of fifty patients with spastic hemiplegia. Responses in the muscles were evoked during voluntary muscle contraction (about 20% of maximum voluntary effort) by submaximal but suprathreshold electrical stimulation of the median (at the wrist) and common peroneal (at the neck of the fibula) nerves respectively. Three EMG peaks (R1, R2 and R3) could be recorded after the direct muscle response (M). There was only a slight difference in R1-R2 latency interval of about 5 ms between upper and lower limbs on the unaffected side of the patients making it unlikely that this late response of the lower limb involves a long loop pathway, although this possibility cannot be discounted for the later, R3, response. Reflex behaviour was analysed for three clinical identifiable recovery stages of voluntary movements in the spastic limbs (synergistic, isolated and useful movements). The major finding was that an increase in the amplitude of the early response "R1" was associated with a decreased amplitude and delayed latency of the late response "R2" on the spastic side. The amplitude of R1 in the three different recovery stages decreased significantly, whereas the amplitude of R2 increased significantly with improvement of the functional stage of the limb. A significant negative linear correlation was found between R1 and R2 amplitude changes in upper as well as lower limbs. A refractoriness of the motor neuron pool as a possible explanation for the decreased R2 amplitude could be discounted. These findings together with recent work on reflex development in children support the hypothesis of reciprocal modulation of early and late reflex signals by supraspinal motor centers.