Correcting for Body Surface Area Identifies the True Prevalence of Abdominal Aortic Aneurysm in Screened Women.

OBJECTIVE: Recently, the prevalence of abdominal aortic aneurysm (AAA) using screening strategies based on elevated cardiovascular disease (CVD) risk was reported. AAA was defined as a diameter ≥30 mm, with prevalence of 6.1% and 1.8% in men and women respectively, consistent with the widely reported AAA predominant prevalence in males. Given the obvious differences in body size between sexes this study aimed to re-evaluate the expanded CVD risk based AAA screening dataset to determine the effect of body size on sex specific AAA prevalence. METHODS: Absolute (26 and 30 mm) and relative (aortic size index [ASI] equals the maximum infrarenal aorta diameter (cm) divided by body surface area (m2), ASI ≥ 1.5) thresholds were used to assess targeted AAA screening groups (n = 4115) and compared with a self reported healthy elderly control group (n = 800). RESULTS: Male AAA prevalence was the same using either the 30 mm or ASI ≥1.5 aneurysm definitions (5.7%). In females, AAA prevalence was significantly different between the 30 mm (2.4%) and ASI ≥ 1.5 (4.5%) or the 26 mm (4.4%) thresholds. CONCLUSION: The results suggest the purported male predominance in AAA prevalence is primarily an artefact of body size differences. When aortic size is adjusted for body surface area there is only a modest sex difference in AAA prevalence. This observation has potential implications in the context of the ongoing discussion regarding AAA screening in women.

Deficit in late-stage contingent negative variation provides evidence for disrupted movement preparation in patients with conversion paresis.

Conversion paresis is the presence of unexplained weakness without detectable neuropathology that is not feigned. To examine the 'abnormal preparation' and 'disrupted execution' hypotheses proposed to explain the movement deficits in conversion paresis, electroencephalographic, electromyographic and kinematic measures were recorded during motor preparation and execution. Six patients with unilateral upper limb conversion weakness, 24 participants feigning weakness and 12 control participants performed a 2-choice precued reaction time task. Precues provided advance information about the responding hand or finger. Patients and feigners demonstrated similar diminished force, longer movement time and extended duration of muscle activity in their symptomatic limb. Patients showed significantly suppressed contingent negative variation (CNV) amplitudes, but only when the symptomatic limb was precued. Despite the similarity in performance measures, this CNV suppression was not seen in feigners. Diminished CNV for symptomatic hand precues may reflect engagement of an inhibitory mechanism suppressing cortical activity related to preparatory processes.

Theta priming of 1-Hz rTMS in healthy volunteers: effects on motor inhibition.

Originally derived from animal experiments, the concept of priming in repetitive transcranial magnetic stimulation (rTMS) experiments refers to a pretreatment or preprotocol stimulation that enhances the effect of the protocol. This means that previous stimulation or bout of activity predisposes the synapse for a second stimulation protocol to produce an enhanced depression. The purpose of this study was to investigate the use of theta priming with 1-Hz rTMS to the motor cortex to induce corticospinal inhibition. The main question was whether there was any benefit in using theta priming instead of simply a longer period of 1-Hz rTMS. To address this, the authors compared 1-Hz rTMS with and without theta priming, using a protocol in which the total period of stimulation was the same. Eleven healthy volunteers were given rTMS to the right primary motor cortex in three separate sessions, in which the participant received one of the three protocols: (1) 1-Hz rTMS for 10 minutes, (2) 5 minutes of 6-Hz theta burst priming followed by 5 minutes of 1-Hz rTMS, or (3) 10 minutes of 1-Hz sham rTMS using a placebo coil. There was a significant effect of active 1-Hz rTMS alone on both resting motor evoked potential and active motor evoked potential amplitude, P < 0.05: both were significantly decrease after 1-Hz rTMS compared with sham. Resting motor evoked potential amplitude was unchanged compared with sham rTMS after the priming protocol, P = 0.001; 1-Hz rTMS with and without theta priming significantly reduced right unimanual reaction time compared with sham. While theta priming abolished or interfered with the inhibitory effect of 1-Hz rTMS on corticospinal excitability, the effect on ipsilateral reaction times was unaffected. The negative effect of priming can be interpreted as a functional interference of the priming preprotocol with the 1 Hz protocol.

Distinct modulation of event-related potentials during motor preparation in patients with motor conversion disorder.

OBJECTIVE: Conversion paresis patients and healthy people feigning weakness both exhibit weak voluntary movement without detectable neuropathology. Uniquely, conversion patients lack a sense of conscious awareness of the origin of their impairment. We investigated whether conversion paresis patients show distinct electroencephalographic (EEG) markers associated with their unconscious movement deficits. METHODS: Six unilateral upper limb conversion paresis patients, 12 feigning participants asked to mimic weakness and 12 control participants performed a precued reaction time task, requiring movements of either hand, depending on precue information. Performance measures (force, reaction and movement time), and event-related EEG potentials (ERP) were compared, between groups and across hands or hemisphere, using linear mixed models. RESULTS: Feigners generated the same inter-hand difference in reaction and movement time as expressed by patients, even though no specific targets were set nor feedback given on these measures. We found novel ERP signatures specific to patients. When the symptomatic hand was precued, the P3 ERP component accompanying the precue was dramatically larger in patients than in feigning participants. Additionally, in patients the earlier N1 ERP component was diminished when the precue signalled either the symptomatic or asymptomatic hand. CONCLUSIONS: These results are consistent with previous suggestions that lack of awareness of the origin of their symptoms in conversion disorder patients may result from suppression of brain activity normally related to self-agency. In patients the diminished N1 to all precues is consistent with a generalised reduction in cognitive processing of movement-related precues. The P3 enhancement in patients is unlikely to simply reflect changes required for generation of impaired movements, because it was not seen in feigners showing the same behavioural deficits. Rather, this P3 enhancement in patients may represent a neural biomarker of unconscious processes, including additional emotional loading, related to active suppression of brain circuits involved in the attribution of self-agency.

A rat model of Urtica ferox neuropathy.

A species of stinging nettle, Urtica ferox, is indigenous to New Zealand and has caused deaths in animals and humans. We previously reported a human case of acute polyneuropathy due to U. ferox stings. We developed an experimental animal model of U. ferox toxin neuropathy to determine its neurophysiological and pathological characteristics. Male Wistar rats received either normal saline or fluid from U. ferox trichomes by injection into the epineurium of the left sciatic nerve. Neurophysiological and histological studies were carried out 5, 14 and 28 days after administration. Toxin-injected rats developed paresis of the left leg by 14 days with recovery by 28 days. Compound muscle action potentials amplitudes on the left side of toxin-administered rats at day 14 were significantly reduced compared to the right uninjected side. Toxin-injected nerves at days 5 and 14 showed a reduction in the number of myelinated fibres compared to the saline-injected nerves and frequency distributions of myelinated fibres showed a shift to smaller fibres. U. ferox neurotoxin thus produced a transient neuropathy in rat peripheral nerves with neurophysiological and pathological features suggestive of axonopathy. The identity and mechanism of action of the toxin responsible for neuropathy are uncertain.

Normative values for three clinical measures of motor performance used in the neurological assessment of sports concussion.

Postural control and motor coordination are essential components of normal athletic activity. Tasks involving balance and coordination are used to determine neurological function in sports-related concussion. Determining normative values for these tasks is therefore essential to provide sports medicine professionals with a frame of reference with which to interpret clinical measures obtained from players suspected of sustaining a concussion. One hundred and seventytwo healthy subjects (16-37 yrs) performed three timed tests: Tandem Gait (TG); Finger-to-Nose (FTN); Single-Leg-Stance (SLS) on firm and foam surfaces. Unadjusted geometric means (+/-SD) for each measure were averaged across three trials. Time to complete TG was 11.2+/-1.2s. FTN for the dominant and non-dominant arm were 2.9+/-1.1s and 3.0+/-1.2s, respectively. SLS values for dominant and non-dominant leg were 20.4+/-3.0s (firm), 3.4+/-1.6s (foam), and 21.0+/-2.9s (firm), 3.3+/-1.6s (foam), respectively. For TG, there was an order effect (P<.001) but no age, sex or BMI effects. FTN demonstrated a dominant arm preference (P<.001), sex (P=.006), BMI (P=.043) and order effects (P<.001). SLS demonstrated an order effect on the firm surface (P=.009) and an order (P<.001) and BMI (P=.001) effect on foam. Intra-rater reliability, as measured by ICC (3,3), demonstrated that TG and FTN had excellent reliability compared to SLS. FTN and TG should continue to be used in test batteries to determine neurological function in sports-related concussion.

Urtica ferox neuropathy.

A 21-year-old student developed an acute, symmetrical, predominantly motor polyneuropathy within 48 h of walking through a patch of nettles (Urtica ferox). Two companions had similar but less severe symptoms. Nerve conduction studies demonstrated markedly reduced compound muscle action potentials and prolonged distal motor latencies. Recovery occurred over a period of a few weeks. This case demonstrates that cutaneous exposure to Urtica ferox can cause an acute polyneuropathy and that its stinging hairs contain an unidentified neurotoxin.