Randomized Pilot Study of Transcutaneous Electrical Nerve Stimulation for Neuropathic/Nociplastic Ocular Pain.

PURPOSE: Transcutaneous electrical nerve stimulation (TENS) is a non-invasive, non-pharmacologic therapy with efficacy in treating chronic pain. This study evaluated the analgesic effectiveness of TENS in individuals with chronic neuropathic/nociplastic ocular pain (NOP) and explored predictors of response.

DESIGN

Prospective, randomized, controlled pilot study

PARTICIPANTS

Thirty-seven individuals (mean age 58 ± 12 years, 51% female) with moderate to severe chronic NOP.

METHODS

Participants were randomized (2:1) to a 20-minute high-frequency TENS (hfTENS, 60 Hz) or low-frequency TENS (lfTENS, 3 Hz) intervention, delivered at the forehead three times/week, for six months. Study visits occurred at baseline, three, and six months, during which data from ocular symptom questionnaires, quantitative sensory testing (QST), and ocular examinations were collected.

MAIN OUTCOME MEASURES: The primary outcome was change in ratings of pain intensity (0-10 numerical rating scale [NRS]). Secondary outcomes included changes in other measures of NOP symptom severity, QST metrics assessing evoked somatosensory sensitivity, and ocular signs (eg, corneal staining).

RESULTS

Both hfTENS and lfTENS significantly reduced eye pain intensity acutely (within 24-hours of initial treatment), and hfTENS produced long-lasting improvements in the NPSI-Eye subscores of pressing pain (2.50 [5.50] to 1.50 [2.50], p = .03) and paroxysmal pain (1.50 [3.50] to 0.00 [1.50], P = .02) at three months, though without corresponding changes in NRS scores of generalized ocular pain intensity. No changes were noted at six months, and neither intervention impacted ocular exam findings at any time point. Significant baseline predictors of long-term TENS response included lower NPSI-Eye scores and lower sensitivity to noxious heat stimuli.

CONCLUSIONS

Both hfTENS and lfTENS effectively reduced NOP short-term, with hfTENS also demonstrating sustained analgesia for neuropathic-like symptoms at three months. Baseline NOP severity and cutaneous sensitivity were predictive of treatment response and suggest reduced disruption of central pain modulatory mechanisms is efficacious for susceptibility to hfTENS analgesia. Together, the results from this pilot study highlight the potential of TENS as a neuromodulatory treatment for NOP, warranting future studies to guide patient selection and optimization of therapeutic benefit.

CLINICAL TRIAL REGISTRATION: Pilot Study of TENS for Ocular pain; NCT05531643.