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This review has pointed out the morphologic differences in the pediatric population and the special subset of disorders of this group that are important for EMG studies and diagnosis of muscle disorders in this population. The size of the patient coupled with the process of myelination means that normative values must be available for each age group. The disorders discussed are generally encountered first in the pediatric population. The electromyographer who sees pediatric cases, must be aware of these disorders. The most commonly observed disorders have been described briefly and the most important signs have been presented differentiating the various pediatric neuromuscular disorders. [ABSTRACT FROM AUTHOR]

Somatosensory evoked potentials were recorded over the lumbar spine and scalp in 12 normal subjects after stimulating the posterior tibial nerve at the knee and ankle and the sural nerve at the ankle. The H-reflex from the soleus muscle was recorded at the same time. The effects of stimulus intensity, frequency of stimulation and vibration were assessed. It was concluded that when the posterior tibial nerve was stimulated in the popliteal fossa, three negative peaks were recorded over the lumbosacral area. They arose from activity in the dorsal roots, the dorsal horn of the spinal cord (SD) and the ventral roots. In contrast when the posterior tibial nerve and the sural nerve were stimulated at the ankle only two negative peaks were recorded, a dorsal root potential and a spinal cord dorsum potential. In addition the data suggested that the peripheral nerve fibres that are involved with generating the surface recorded spinal potential with mixed nerve stimulation are primarily muscle afferents. [ABSTRACT FROM AUTHOR]

The sympathetic skin response (SSR) was measured in 33 patients with peripheral neuropathies and in 30 normal control subjects. Abnormalities of the response were correlated with clinical, pathologic, and EMG observations. The response was usually absent in axonal neuropathies, but present in demyelinating disorders. Abnormalities of the sympathetic skin response did not correlate well with clinical evidence of dysautonomia, but were a reliable indicator of disorders affecting unmyelinated axons. [ABSTRACT FROM AUTHOR]

A study of 10 patients with brachial plexus trauma was performed to determine whether the diagnostic accuracy of sensory evoked potentials (SEPs) may be improved by using stimulation of multiple peripheral nerves (median, radial, musculocutaneous and ulnar). In addition, the relative advantages of SEPs and peripheral electrophysiological studies were considered. SEP patterns following most common brachial plexus lesions were predictable. Injuries to the upper trunk affected the musculocutaneous and radial SEPs predominantly. Lower trunk or medial cord lesions primarily affected ulnar SEPs. Diffuse brachial plexus lesions affected SEPs from all stimulation sites. In the majority of cases, the necessary information was obtainable from conventional EMG: however, for lesions involving the upper segments only, SEP techniques were more useful. It is suggested that selective SEPs from appropriate peripheral nerves when interpreted in combination with conventional EMG may add useful additional information. [ABSTRACT FROM AUTHOR]

The usefulness of performing late response studies for the detection of peripheral nerve dysfunction has been demonstrated. It has been shown that significant prolongation of the minimal latencies of the H reflex and the F response is present at a time when conventional methods of motor and sensory conduction do not show an abnormality in individual patients. Abnormalities of late responses have been shown to occur in a variety of peripheral neuropathies with "axonal" as well as "segmental demyelination" type of underlying pathology. [ABSTRACT FROM AUTHOR]

Patients with Parkinson's disease performed several different stereotyped elbow flexion tasks, and the electromyographic (EMG) patterns from biceps and triceps were compared with previously established normal standards. The EMG pattern during a smooth flexion task was almost always abnormal and was characterized by alternating activity in biceps and triceps. The EMG patterns during a fast flexion task were also usually abnormal although they were always composed of bursts of EMG activity of normal duration appearing alternately in the agonist and antagonist muscles. These bursts, associated with movements of the limb, have a superficially similar appearance to the EMG bursts seen with tremor-at-rest, but certain physiological differences are demonstrated. This study demonstrates that both slow (ramp) and fast (ballistic) movements are clearly abnormal in these patients with disease of the basal ganglia. In a task designed to investigate antagonist inhibition before agonist activity, a majority of the patients performed normally. This suggests that, contrary to previous claims, slowness of movement (akinesia/bradykinesia) is not due either to failure to relax or to rigidity of antagonist muscle. [ABSTRACT FROM AUTHOR]

Physiological and pharmacological studies of more than 150 patients with movement disorders are reported. Particular attention is paid to the differentiation of various types of tremor on the basis of rate, rhythm, and pattern of EMG activity in antagonistic muscles. The typical 'tremor-at-rest' of Parkinson's disease--3-7 Hz activity which alternates between antagonistic muscles--is suppressed, at least briefly, during voluntary activity, at which time typical 8--12 Hz 'physiological tremor' may be seen. Essential tremor and its familial or senile variants also have a characteristic EMG pattern during voluntary activity--5-8 Hz bursts of activity which are synchronous in antagonistic muscles. This type of tremor may also be present in patients with Parkinson's disease and in certain kinships with a Charcot-Marie-Tooth polyneuropathy. Other tremors in association with polyneuropathy ('neuropathic tremor') have different physiological characteristics. Myoclonus is of essentially two types ('positive' with EMG bursts and 'negative' with brief pauses in ongoing activity, as with asterixis) and may, at times, mimic tremor. Certain specific tremors respond predictably to specific pharmacological therapy. [ABSTRACT FROM AUTHOR]

EMGs from biceps and triceps were recorded during stereotyped elbow flexion tasks performed by 20 patients fulfilling clinical criteria for 'cerebellar deficits' and the data were compared with previously established normal standards. In a fast flexion task, 15 of 18 patients showed prolongation of the initial biceps and/or triceps components, and it is suggested that this abnormality might be an elemental feature of dysmetria. Ten of 14 patients showed the normal pattern of smooth flexion indicating that, with cerebellar deficits, smooth movements are better preserved than fast movements. The timing of the cessation of triceps activity before the initiation of biceps activity in an alternating movement was abnormal in 12 of 16 patients; this abnormality might be an elemental feature of dysdiadochokinesia. [ABSTRACT FROM AUTHOR]

EMG activity was recorded in biceps and triceps while subjects voluntarily flexed their elbows during a visual matching task. With fast flexion, the initial EMG was characterized by a triphasic pattern with a burst of activity first in biceps, then in triceps with a silent period in biceps, and finally in biceps again; these components were analysed quantitatively. Smooth flexion was characterized by continuous activity in biceps. Inhibition of tonic activity of triceps in relation to a fast flexion occurred in the 50 ms before the initiation of biceps activity. A patients with a severe pansensory neuropathy performed normally on these tasks. Physiological mechanisms underlying these patterns are analysed; an important conclusion is that the triphasic activity with fast flexion is 'centrally programmed'. [ABSTRACT FROM AUTHOR]

One type of flexor reflex, that recorded from the tibialis anterior muscle in response to electrical stimulation of the sole of the foot, was studied in normal subjects and patients with several neurological disorders. Normally this reflex consists of two components, the second of which is related to the actual withdrawal. The first component, normally of lower threshold, is difficult to evoke in patients with chronic spinal cord or discrete cerebral lesions, whereas it has an unusually low threshold and is very clearly seen in those with Parkinson's disease. In patients with spinal cord disease, the exaggerated flexor reflexes are seen at long latencies after relatively small stimuli. During the early phase of recovery from spinal transection, both components may be seen and are, therefore, spinal in origin. Studies of patients with the sensory neuropathy of Friedreich's ataxia suggest that the afferent fibres responsible for these flexor reflexes are the small myelinated fibres. Recovery curves demonstrate very long-lasting changes in flexor reflex excitability in normal subjects and patients with `spasticity' from spinal lesions. This differs in patients with `spasticity' from lesions rostral to the brain-stem. Examples in man of such physiological phenomena as reciprocal inhibition, local sign, habituation, temporal and spatial summation are discussed. [ABSTRACT FROM AUTHOR]

Physiological and biochemical studies were carried out on 16 patients with motor neurone disease (MND). It was confirmed that the peripheral nerves in cases of MND are often unusually resistant to ischaemia especially as regards the large sensory fibres. Biochemical investigations demonstrated a tendency to carbohydrate intolerance and abnormal pyruvate metabolism. When compared with other related studies in MND it seems very likely that there is a metabolic abnormality present in MND which demands further study. [ABSTRACT FROM AUTHOR]

A detailed study of the human blink reflex in the different parts of the orbicularis oculi muscle has been carried out. The first component of the blink reflex has been demonstrated in patients with Friedreich's ataxia, who have selective loss of large sensory fibres resulting in loss of proprioceptive input. It has been established that both components of the blink reflex are cutaneous reflexes which represent a highly organized and purposeful mechanism in man. Afferent fibres for the blink reflex have been identified in the human supraorbital nerve and their conduction velocity has been estimated for the first time in man. It has been demonstrated that both components of the blink reflex are mediated by the same group of afferent fibres. [ABSTRACT FROM AUTHOR]

Flexor reflex afferent nerve fibres have been identified in the mixed peripheral nerve and measurement of their conduction velocity has been carried out. It has been demonstrated that the flexor reflex afferent fibres have a higher threshold of stimulation than the motor fibres supplying the foot muscles. The effect of conditioning volleys in the flexor reflex afferent fibres on the H reflex has been determined and reciprocal inhibition of extensor motoneurones has been found to be related to the second component of the flexor reflex. [ABSTRACT FROM AUTHOR]