Serum HSP70 Levels in Sudden Sensorineural Hearing Loss and Their Modulation after Hyperbaric Oxygen Therapy: A Prospective Controlled Study

ObjectiveSudden sensorineural hearing loss (SSNHL) has been linked to inflammatory, hypoxic, and cellular stress pathways. Heat shock protein 70 (HSP70) is a stress-responsive molecular chaperone that may reflect systemic biological stress activation during inner ear injury. This prospective study aimed to characterize serum HSP70 dynamics during hyperbaric oxygen therapy (HBOT) in SSNHL and to compare these changes with those observed in patients receiving HBOT for non-otologic indications.MethodsThis prospective, non-randomized controlled study included 50 patients: 25 with SSNHL (Group 1) and 25 receiving HBOT for non-SSNHL indications (Group 2). HBOT was administered at 2.4 ATA for 120 minutes per session, 5 days per week, for 20 sessions. Serum HSP70 concentrations were measured by sandwich ELISA immediately before the first HBOT session and after completion of the 20th session. Pure-tone audiometry was performed before and after treatment in the SSNHL group, and recovery was classified according to Siegel criteria. In routine otolaryngology practice, systemic corticosteroid therapy was initiated immediately after SSNHL diagnosis, whereas HBOT was added as soon as possible after referral to the hyperbaric unit; however, referral timing varied across patients. Therefore, because nearly all SSNHL patients received systemic corticosteroids and no steroid-only comparator was included, audiometric findings were interpreted descriptively rather than as evidence of the independent efficacy of HBOT.ResultsIn the SSNHL group, mean pure-tone average improved from 62.44±19.72 dB HL to 31.76±27.85 dB HL after treatment (p<0.001), and earlier HBOT initiation was associated with a more favorable recovery distribution (p=0.007). Baseline serum HSP70 levels were higher in SSNHL than in the non-SSNHL HBOT group (249.84±76.69 vs 192.00±89.14 ng/mL; p=0.03). After treatment, serum HSP70 levels decreased significantly in both groups (both p<0.001), whereas the percentage reduction did not differ significantly between groups (17.15±8.72% vs 20.84±15.15%; p=0.99). No HBOT-related adverse events were observed.ConclusionSSNHL was associated with higher circulating HSP70 levels than non-SSNHL HBOT indications, supporting the presence of increased systemic stress activation. HBOT was accompanied by a significant reduction in serum HSP70 in both groups, suggesting that circulating HSP70 may reflect treatment-related systemic stress modulation in addition to disease-related biology. Given the non-randomized design, concomitant corticosteroid use, and absence of a steroid-only comparator, the audiometric findings should not be interpreted as demonstrating the independent therapeutic effect of HBOT.