Mixed silent period (MSP) and cutaneous silent period(CSP) in diagnostic of a severe carpal tunnel syndrome

Reykjavik 26th of July 2017

by Neurophysiology Plus Iceland

Cutaneous silent period can be preserved in entrapment neuropathies (KofIer et al 2003). It is known that the more severe the neuropathy is, the more impairment of A-delta fibers can be found (Duarte et al 2016). In patient with severe CTS the mean onset latency was increased to 85.0 ms (SD 8.7 ms, P < 0.01) Silvpauskaite et al 2005.

CASE REPORT (here) Patient 66 year-old with motor weakness in hands and hypoesthesia

This case was published in Neurophysiology Plus Iceland informal group e-Bulletin (here)

Right median nerve mixed and cutaneous (palm) silent period

Cutaneous Silent Period from 2 digit sensory branches (ring electrodes)

Cutaneous Silent Period from 2 digit sensory branches in examinator (OCB), normal values

After we diagnosed very severe CTS in the right side and severe CTS in the left we performed A-delta & alpha motorneurons driven CSP from 2 digit and there was no clear inhibition of the voluntary contraction (onset 107ms). Then, we checked again from the palm-thenar region and we observed CSP with onset 100ms, end 155 ms and 55ms duration. Also a clear silent period was obtained after stimulation from the wrist, the mixed median nerve and record from abductor pollicis brevis.

Conclusion: Sensory fibers (small and fast) are the last in be damaged and the injury do not occurred at the wrist carpal tunnel as it happened with axonal loss of the large sensory fibers.  At this moment there is not clear if those fibers are only the A-delta or there might be another sensory input by direct electrical stimulation of other fiber type (proprioceptors?, muscle spindles?)

Nerve Conduction Studies: 2017 © Neurophysiology Plus Iceland