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The levels o f voluntary EM G recorded from the stroke side were lower than the non­ stroke side for all patients when maintaining a sustained contraction o f approximately 20% MVC from that side. O n the stroke side, values for the average rectified EM G recorded

from patients with poor recovery were often as litfie as 6-lOpV indicating very low levels

o f m otoneurone activity. This raises the question as to w hether abnormalities in the CMRs for these patients might in some way be related to such low levels o f activation. However a num ber o f lines o f evidence do not suggest that this is the case. Recordings from a healthy subject at levels o f average rectified EM G which were comparable with the weakest stroke

patients (ie ~10p.V; 2-3% MVC) showed that the normal triphasic responses were consistently present. Similar results were shown w hen concentric needle electrodes were used to record from only a small num ber o f m otor units in ID I (Evans et al 1989). Furtherm ore, G arnett & Stephens (1980) investigated CMR reflex com ponents recorded from high or low threshold m otor units in response to cutaneous stimulation using single m otor unit recordings. Results showed that w hen digital nerves were stimulated at 4T, the sizes o f the II and E2 responses were larger for units recruited at low contraction strengths com pared with units recruited at high contraction strengths. In addition the sizes o f the E l

com ponents were relatively smaller for m otor units with longer contraction times. These low threshold units were recruited at less than 0.5% MVC. Therefore, on the basis o f these findings, it would be expected that for patients with poor recovery w ho probably were only able to recruit low threshold m otor units, the E l com ponents would be smaller and II and E2 com ponents would be larger, but in fact the opposite result was shown.

Predicting outcome after stroke

The prognosis for recovery after stroke is extremely variable and it is difficult to predict the clinical outcom e during the early stages after stroke. Magnetic resonance imaging (MRI) has been used to identify the size and the site o f the lesion and, in addition, magnetic resonance spectroscopy can be used in conjunction with MRI to evaluate biochemical changes in area surrounding an infarct (Prichard, 1994). The volum e o f the infarct has been shown to be related to patient outcome, and it was observed that for patients with an infarct in the middle cerebral artery territory, those w ho were independent at 3 m onths had

smaller infarcts than patients who were dependent or dead (Saunders et al 1995). Pereira

et al. (Pereira et al. 1999) showed that patients with infarcts within the middle cerebral

artery territory which exceeded 70ml in volume were likely to make a poor recovery. Magnetic resonance spectroscopy was also used to evaluate biochemical changes in the core and surrounds o f the area o f ischaemia shown on MRI, in particular to measure the levels o f N-acetyl aspartate (NAA) which if decreased, can be used as a marker o f neuronal or axonal damage. It was dem onstrated that for patients with infarcts o f less that 70ml, those with residual NAA concentrations o f greater than 7mM had a good outcom e but those with a core level o f NAA which was less than this were either dead or dependent at 3

m onths (Pereira et al. 1999). These studies enable the prediction o f overall clinical

outcom e in patients presenting during the first few days following stroke, rather than being specifically related to m otor functional recovery o f the upper limb. However, recently

Pendlebury et al (Pendlebury et al. 1999) investigated NAA loss in a functional pathway,

the descending m otor tracts, and these authors revealed a strong correlation between loss o f NAA and m otor im pairment following infarction in the internal capsule. More recendy, the same group used MR images to determine lesion volume and developed a template o f

corticospinal template which was occupied by the stroke lesion (Pineiro et al. 2000). This m ethod was superior to measuring the relationship between the volume o f the infarct and m otor deficit especially for patients with small strokes. However, this study was retrospective and examined patients between 1 m onth and 5 years after stroke so prospective studies are needed to confirm the value o f this technique for predicting m otor function outcome.

O ther neurophysiological tools which have proved useful for predicting m otor recovery include transcranial magnetic stimulation. It is generally agreed that if TMS to the m otor cortex early after stroke evokes a response in hand muscles during voluntary activation or

at rest, this indicates a good prognosis for subsequent recovery o f hand function (Turton et

al. 1996; Rapisarda et al 1996; Escudero et al 1998; Cruz-Martinez et al 1999; Vang et al

1999; Pennisi et al 1999). Initial testing after stroke was perform ed within 48 hours

(Pennisi et al 1999; Rapisarda et al 1996; Vang et al 1999), 1 week (Escudero et al. 1998;

Cruz-Martinez et al 1999) and 5 weeks (Turton et al 1996). TMS was particularly useful

for identifying patients likely to make some functional m otor recovery in the hand but who at initial testing lacked the ability to perform any voluntary contraction o f ID I (Turton et al 1996) or o f thenar muscles (Escudero et al. 1998). Excitation thresholds required to produce a response to TMS in ID I and abductor digiti rninirni (ADM) have also been investigated in a large num ber o f stroke patients. Results showed that if the excitability threshold remained raised on the stroke hemisphere com pared with the non-stroke hem isphere at 30 days after stroke and showed no reduction in relation to the excitation

threshold at day 7 after stroke, this was predictive o f a poor functional outcom e (Catano et

al 1996). A nother study by the same group also showed that a reduction in the silent

period duration obtained from ID I following TMS at day 7 following stroke was predictive

o f the a poor outcom e and the eventual occurrence o f spasticity (Catano et al 1997).

A small study has examined SSEPs to try to predict functional outcom e after stroke (Fierro

et al 1999). Results showed that the amplitudes o f the P15-N20 and N20-P25 com ponents

o f SSEPs in response to median nerve stimulation were significantly smaller on the affected hem isphere at the first assessment 3 weeks after stroke. Significant correlations were shown betw een the amplitude o f the N20-P25 com ponents and muscle strength and between the P15-N20 com ponents and the Barthel score. Overall, abnormal amplitudes o f SSEPs at 3 weeks after stroke predicted m otor and functional im pairm ent at 3 months.

How do findings from other neurophysiological studies relate to the present study