Cortical relay time for long latency reflexes in patients with definite multiple sclerosis.

BACKGROUND

Long latency reflexes (LLR) include afferent sensory, efferent motor and central transcortical pathways. It is supposed that the cortical relay time (CRT) reflects the conduction of central transcortical loop of LLR. Recently, evidence related to the cortical involvement in multiple sclerosis (MS) has been reported in some studies. Our aim was to investigate the CRT alterations in patients with MS.

METHODS

Upper extremity motor evoked potentials (MEP), somatosensory evoked potentials (SEP) and LLR were tested in 28 patients with MS and control subjects (n=22). The patients with MS were classified according to the clinical form (relapsing-remitting [R-R] and progressive groups). The MS patients with secondary progressive and primary progressive forms were considered as the "progressive" group. CRT for LLR was calculated by subtracting the peak latency of somatosensory evoked potentials (SEP) and that of motor evoked potentials (MEP) by transcranial magnetic stimulation from the onset latency of the second component of LLR (LLR2) (CRT = LLR2 - [MEP latency + N20 latency])

RESULTS

Cortical relay time was calculated as 7.4 +/- 0.9 ms in control subjects. Cortical relay time was prolonged in patients with MS (11.2 +/- 2.9 ms) (p<0.0001). The latencies of LLR, MEP and SEP were also prolonged in patients with MS. Cortical relay time was not correlated with disease severity and clinical form in contrast to other tests.

CONCLUSIONS

Our findings suggested that CRT can be a valuable electrophysiological tool in patients with MS. Involvement of extracortical neural circuits between sensory and motor cortices or cortical involvement due to MS may cause these findings.