H-reflex to S1-root stimulation improves utility for diagnosing S1 radiculopathy

Area of Science:

• Neuroscience
• Clinical Electrophysiology
• Neurology

Background:

• The H-reflex, elicited by tibial nerve stimulation, is standard for diagnosing S1 radiculopathy but has limited sensitivity due to long reflex latencies.
• Small changes from focal S1 root pathology can be obscured within the overall reflex latency, reducing diagnostic precision.

Purpose of the Study:

• To investigate if stimulating the S1 nerve root directly at the S1 foramen improves the diagnostic utility of the H-reflex for S1-root lesions.
• To compare the sensitivity of S1-root H-reflex stimulation versus traditional tibial nerve H-reflex stimulation in patients with S1 radiculopathy.

Main Methods:

• A randomized paired-study design compared H-reflexes from tibial nerve stimulation and S1-root stimulation in 55 patients with confirmed unilateral S1 radiculopathy.
• High-voltage electrical stimulation was used to elicit H-reflexes bilaterally at the S1 foramen and L4/L5 levels.
• Latencies, specifically the H-reflex to M-wave interval (HMI), were compared to normal values and asymptomatic contralateral limbs.

Main Results:

• S1-root stimulation revealed abnormal responses in 54 of 55 symptomatic patients, compared to 39 with abnormal tibial nerve H-reflexes.
• On the asymptomatic side, 52 of 55 patients had normal S1-root H-reflex responses, with three showing abnormalities.
• Stimulation at the L4/L5 level helped localize lesions to the L5/S1 spine level in some patients with absent S1-foramen H-reflexes.

Conclusions:

• Direct S1-root H-reflex stimulation demonstrates superior sensitivity in detecting S1 radiculopathy compared to tibial nerve stimulation.
• Abnormal S1-root H-reflexes can identify S1 root lesions even when tibial nerve H-reflexes are normal, enhancing diagnostic sensitivity.
• This technique aids in localizing the lesion site, improving diagnostic specificity for S1 compressive radiculopathies.