Post-stroke fatigue: a problem of altered corticomotor control?

OBJECTIVES: We recently showed that diminished motor cortical excitability is associated with high levels of post-stroke fatigue. Motor cortex excitability impacts movement parameters such as reaction and movement times. We predicted that one or both would be influenced by the presence of post-stroke fatigue. METHODS: 41 first-time stroke survivors (high fatigue n=21, Fatigue Severity Scale 7 (FSS-7) score >5; low fatigue n=20, FSS-7 score <3) participated in the study. Movement times, choice and simple reaction times were measured in all participants. RESULTS: A three way ANOVA with fatigue (high and low), task (movement time, simple reaction time and choice reaction time) and hand (affected and unaffected) as the three factors, revealed a significant difference between affected (but not unaffected) hand movement times in the high compared to low fatigue groups. Reaction times, however, were not different between the high-fatigue and low-fatigue groups in either the affected or unaffected hand. CONCLUSIONS: Previously, we showed that motor cortex excitability is lower in patients with high post-stroke fatigue. Our current findings suggest that post-stroke fatigue (1) is a problem of movement speed (possibly a consequence of diminished motor cortex excitability) and not movement preparation, and (2) may have a focal origin confined to the lesioned hemisphere. We suggest that low motor cortex excitability in the lesioned hemisphere is a viable therapeutic target in post-stroke fatigue.

Bordetella pertussis in a neonatal intensive care unit: identification of the mother as the likely source.

Bordetella pertussis, the cause of whooping cough, is highly contagious. A female, twin 1, born at 34 weeks of gestation and present on a neonatal intensive care unit for 19 days, became apnoeic and bradycardic. A pernasal swab, sent when pertussis was clinically suspected, grew B. pertussis. Twin 2 had similar symptoms. The mother admitted having a prolonged cough. Polymerase chain reaction of pernasal swabs was positive for both twins, and the mother had positive pertussis serology. An incident management committee was convened. Fifty neonates and 117 healthcare workers were identified as contacts and were offered information, azithromycin chemoprophylaxis and/or pertussis vaccination according to UK national guidelines.

Action of 5 Hz repetitive transcranial magnetic stimulation on sensory, motor and autonomic function in human spinal cord injury.

OBJECTIVE: To assess the effectiveness of physiological outcome measures in detecting functional change in the degree of impairment of spinal cord injury (SCI) following repetitive transcranial magnetic stimulation (rTMS) of the sensorimotor cortex. METHODS: Subjects with complete or incomplete cervical (or T1) SCI received real and sham rTMS in a randomised placebo-controlled single-blinded cross-over trial. rTMS at sub-threshold intensity for upper-limb muscles was applied (5 Hz, 900 stimuli) on 5 consecutive days. Assessments made before and for 2 weeks after treatment comprised the ASIA (American Spinal Injuries Association) impairment scale (AIS), the Action Research Arm Test (ARAT), a peg-board test, electrical perceptual test (EPT), motor evoked potentials, cortical silent period, cardiovascular and sympathetic skin responses. RESULTS: There were no significant differences in AIS outcomes between real and sham rTMS. The ARAT was increased at 1h after real rTMS compared to baseline. Active motor threshold for the most caudally innervated hand muscle was increased at 72 and 120 h compared to baseline. Persistent reductions in EPT to rTMS occurred in two individuals. CONCLUSIONS: Changes in cortical motor threshold measures may accompany functional gains to rTMS in SCI subjects. SIGNIFICANCE: Electrophysiological measures may provide a useful adjunct to ASIA impairment scales.

Development of quantitative and sensitive assessments of physiological and functional outcome during recovery from spinal cord injury: a clinical initiative.

The ability to detect physiological changes associated with treatments to effect axonal regeneration, or novel rehabilitation strategies, for spinal cord injury will be challenging using the widely employed American Spinal Injuries Association (ASIA) impairment scales (AIS) for sensory and motor function. Despite many revisions to the AIS standard neurological assessment, there remains a perceived need for more sensitive, quantitative and objective outcome measures. The purpose of Stage 1 of the Clinical Initiative was to develop these tools and then, in Stage 2 to test them for reliability against natural recovery and treatments expected to produce functional improvements in those with complete or incomplete spinal cord injury (SCI). Here we review aspects of the progress made by four teams involved in Stage 2. The strategies employed by the individual teams were (1) application of repetitive transcranial magnetic stimulation (rTMS) to the motor cortex in stable (chronic) SCI with intent to induce functional improvement of upper limb function, (2) a tele-rehabilitation approach using functional electrical stimulation to provide hand opening and grip allowing incomplete SCI subjects to deploy an instrumented manipulandum for hand and arm exercises and to play computer games, (3) weight-assisted treadmill walking therapy (WAT) comparing outcomes in acute and chronic groups of incomplete SCI patients receiving robotic assisted treadmill therapy, and (4) longitudinal monitoring of the natural progress of recovery in incomplete SCI subjects using motor tests for the lower extremity to investigate strength and coordination.

Sweat production and the sympathetic skin response: improving the clinical assessment of autonomic function.

The aim of this project was to establish the relationship between sweat production and the electrodermal events comprising the sympathetic skin response to arousal stimuli. A series of randomly timed magnetic stimuli were applied to the neck of healthy human volunteers. Sympathetic skin responses and the associated sweat responses were recorded from the palms of both hands. Sympathetic skin responses typically had a biphasic shape consisting of a negative initial potential (palm relative to dorsum of hand) followed by a positive deflection. Sweat production was positively correlated with amplitude of the second positive deflection of the sympathetic skin response and negatively correlated with the amplitude of the initial negative deflection. For subjects showing only an initial negative sympathetic skin response, sweat release was low or not detectable. During habituation, the negative initial wave increased relative to the second positive wave, and sweat production fell. The strong correlation between the positive wave of the sympathetic skin response and sweat production suggests that the former may provide a quantitative functional measure of sudomotor activity in situations when it is impractical to measure the amount of sweat produced in the startle response. Thus, the positive component of the biphasic sympathetic skin response may be employed in clinical assessment of the functional efficacy of the sympathetic sudomotor system.

Motor neurone excitability in back muscles assessed using mechanically evoked reflexes in spinal cord injured patients.

OBJECTIVE: The clinical and functional assessment of back muscles in human spinal cord injury (SCI) has received little attention. The aim of this study was to develop a method to assess the level of a thoracic spinal cord lesion based on the reflex activation of back muscles. METHODS: In 11 control subjects and in 12 subjects with clinically complete thoracic SCI (T2-T12), either a spinous process or an erector spinae muscle was prodded to elicit short latency reflexes recorded electromyographically at the spinal level of stimulation. An electromagnetic servo, attached to a blunt probe, applied stimuli at a frequency of 1 Hz and amplitude of 3 mm. Two trials of 50 mechanical prods were conducted at each site. RESULTS: Reflexes were evoked in control subjects in 82% of trials when the spinous process was prodded, and in 80% of trials when the muscle was prodded. In contrast, reflexes in SCI subjects could be elicited in 90-100% of trials two segments either above or below the lesion. Reflex responses in control subjects had a mean (SEM) latency of 5.72 (0.53) ms when the spinous process was prodded, and 5.42 (0.42) ms when the muscle was prodded. In the SCI subjects, responses had slightly (but insignificantly) longer latencies both above and below the lesion to either stimulus. The amplitude of reflex responses, expressed as a percentage of the background EMG, was on average 2-3 times larger at the three vertebral levels spanning the lesion in SCI subjects than at sites above or below the lesion or at any level in control subjects. CONCLUSION: We propose that the size of these mechanically evoked reflexes may be useful in determining the level of thoracic SCI. Furthermore, the reflexes might provide a valuable tool with which to monitor recovery after an intervention to repair or improve function of a damaged spinal cord.

The effect of an energy drink containing glucose and caffeine on human corticospinal excitability.

Glucose- and caffeine-containing energy drinks are said to influence the cognitive and cellular function within the brain. In this study, we have used the size of motor-evoked potentials (MEPs) produced in response to transcranial magnetic stimulation (TMS) of the motor cortex as an index of corticospinal excitability after ingestion of Lucozade and control drinks of glucose-containing or caffeine-containing carbonated water or carbonated water alone. With local ethical approval and informed consent, 10 healthy volunteers took part; surface electromyographic (EMG) recordings were taken from the thenar muscles of the dominant hand. In each assessment, 15 TMS stimuli were delivered over the motor cortex at an intensity of 1.1 T. Six subjects ingested a 380-ml bottle of carbonated Lucozade drink containing 68 g of glucose and 46 mg caffeine. Four subjects took part in three control trials drinking: (A) carbonated water with caffeine, (B) carbonated water with glucose and (C) carbonated water alone. Assessments were made before and at 30-min intervals after each drink. Mean fasting blood glucose concentrations and mean areas of MEPs rose after the Lucozade, remaining elevated for 90 min. Similar rises in MEP areas were seen in trials after drinking carbonated water with caffeine or with glucose, but not after drinking carbonated water alone. No change was seen in the M-wave evoked by electrical stimulation of the ulnar nerve. We conclude that Lucozade can affect the size of MEPs to activation of the motor cortex with fixed-intensity TMS. The underlying mechanism is likely to relate to the combined effects of caffeine and glucose on the brain.