Old technique, new applications: can the H-reflex be a possible real-time indicator in endoscopic surgery for
Marta Rodrigues Carvalho1, Vitor Caldas Marques2, Baldomero Pinto Soares3
1Department of Neurology and Clinical Neurophysiology, Instituto Hospital de Base do Distrito Federal, Brasília, Brazil.
Background:
The Hoffmann (H-) reflex is a monosynaptic electrophysiological response that reflects S1-root integrity. Although widely used in experimental and in clinical outpatient neurophysiological testing, its intra-operative application during endoscopic lumbar surgery is rarely reported. We present the first real-time documentation of H-reflex normalization immediately after endoscopic decompression of an acute L5-S1 disc herniation.
Case Description:
A 49-year-old woman presented with acute right-sided S1 radiculopathy (ankle dorsiflexion/plantar-flexion MRC grade III; hallux extension grade I). MRI showed a large, right sub-articular L5-S1 disc extrusion compressing the S1 nerve root. Unilateral biportal endoscopic discectomy was performed under general anesthesia with multimodal intra-operative neuromonitoring (MEPs, free-run EMG, and continuous tibial-nerve H-reflex). Baseline recordings revealed marked side-to-side asymmetry: right-leg MEP amplitudes were depressed, and the right H-reflex was low and unstable. During foraminoplasty and fragment removal, a sudden, sustained 100% surge in right H-reflex amplitude occurred, coincidence with root decompression, while MEPs remained unchanged. Free-run EMG discharges abated after the H-reflex improved. Post-operative recovery was uneventful. At 2 months the patient demonstrated near-complete motor recovery (MRC IV-V) and full pain relief.
Conclusion:
Continuous H-reflex monitoring provided an immediate, sensitive marker of S1-root decompression when conventional MEPs failed to reflect functional recovery. This single-case experience supports the feasibility and potential prognostic value of adding H-reflex surveillance to the neuromonitoring toolkit for endoscopic lumbar surgery. Prospective studies in larger cohorts are warranted to validate threshold criteria, refine stimulation parameters, and determine cost-effectiveness.
