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SUDDEN DEAFNESS OF UNKNOWN ORIGIN: P. Germonpré, M.D. Abstract Three case reports are presented of Sudden Deafness of Unknown Origin, that responded favorably to Hyperbaric Oxygen Therapy (HBOT) after treatment delays of 7, 10 and 12 days, respectively. Near-complete remissions were obtained in all three patients, despite initial hearing loss of -60 to -80 dBa on all frequencies before the start of HBOT. All patients were treated at 2.5 ATA in a multiplace hyperbaric chamber. One patient received ancillary normovolemic hemodilution and corticoid therapy. Patient data are presented and an overview of the possible causes in these individual patients is given. Introduction Sudden Deafness of Unknown Origin is a diagnosis "per exclusionem". It can be defined as a rapidly (<3 days) progressive, unilateral perceptive hearing loss, often accompanied with tinnitus, in an otherwise healthy patient, where no direct causative agent, predisposing medical condition, or underlying disease process can be demonstrated (1, 2). The medical therapy is in many cases unsuccessfull, and many therapeutic combinations and protocols have been suggested. No consensus exists on the best therapeutic approach. Although Hyperbaric Oxygen Therapy (HBOT) is sometimes advocated, randomised controlled prospective studies are lacking. It is however felt by HBOT clinicians, that the sooner HBOT is instituted, the better the results (3). Institution of HBOT after a delay of more than 7 days is often felt to be of little use. We present three case reports where, despite long delays during which no or insufficient response was obtained with various therapeutics, the association or institution of HBOT resulted in a near-complete recovery of hearing. Case Reports A.M., male, 41 y., presents with a left side perceptive hearing loss and low frequency tinnitus, 4 days after an uneventful SCUBA dive well within the limits of decompression (15 msw, 20 min bottom time), and two days after a swimming pool SCUBA training session (2.5 msw depth). At none of these occasions difficulties with ear equalisation were noted. He is a non-smoker, without history of excessive noise exposure. His medical history is without particularities. Tonal audiometry shows a left pancochlear perceptive hearing loss of -80 dBa. Clinical examination shows no signs of vestibular involvement. A left paracentesis at day 3 yields no retrotympanic liquid. He receives no further treatment untill day 6. Tonal audiometry then shows a -75 dBa global deficit. Blood analysis, posterior fossa CT are normal. A treatment with piracetam 12g i.v. per day, and HBOT (2.5 ATA, 90 min) twice daily, is then instituted. A control audiometry after three days shows a near complete remission (MHL: Mean Hearing Loss on frequencies 250, 500, 1000 and 2000 = -10 dBA), with a small dip at 6000 Hz., which remains identical after completion of the 5 days HBOT. M.M., female, 29 y. presents with a left side perceptive hearing loss, without tinnitus, of the high frequencies (2000, 4000, 8000 Hz: -80dBa). An initial work-up reveals no causative factors. Posterior fossa CT is normal. From her medical history a congenital spherocytosis is retained, which has been asymptomatic after a splenectomy at the age of 12, but with chronically elevated WBC count (13.000 /mm³), and a minor mitral valve insufficiency. Clinical examination is normal, blood analysis shows no signs of active haemolysis. She is treated with betamethason 4mg/day p.o. Despite this, a progression of the hearing loss is noted, and by day +9, a pancochlear loss of -80dBa is present. She is then transferred for adjunctive HBOT. After 5 days of HBOT (2.5 ATA, 90 min, 1x/day), a complete recovery at the low and middle frequencies is noted, with the persistance of a 4000 Hz and 8000 Hz deficit of -60dBa and -40dBa respectively. This remains so after 5 more days of HBOT. There has been no signs of increased haemolysis during HBOT. D.A., female, 26 y., presents with a perceptive hearing loss and low frequency tinnitus of the right ear, two days after an otherwise uneventful SCUBA dive well within the limits of decompression (15 msw, 35 min bottom time). There has been no barotrauma of the ear. She is a non-smoker, bank employee, who is in good health and takes no medication. The personal and familial anamnesis is without particularities. Physical examination, extensive blood analysis, and posterior fossa CT scan are normal. Tonal audiometry shows an important deficit on all frequencies, with a MHL of -70dBa. She is treated with nasal decongestionants and co-dergocrin mesilate p.o. for 5 days, then for 7 days with normovolemic haemodilution, piracetam 12g i.v. and triamcinolon 3x4mg p.o. without significant improvement. HBOT (2.5 ATA, 90 min) twice daily, is then started for 5 days, without further drug treatment. After completion of HBOT, there is a complete recovery of the high frequencies, and a MHL of -25dBa. 2 weeks after completion, a MHL of -10 dBa is measured, and 6 months later, this is confirmed. Discussion Pathogenesis of SD: In cases where no external or internal cause could be determined, the exact pathogenesis of the hearing loss is not known. Possible mechanisms include micro-thrombo-embolism, arterial vasospasm, perilympatic hypertension, viral infection. Whatever the cause, the consequence is in most cases edema formation, with cochlear arterial supply compromise. The final end-point is endo-cochlear hypoxia, which leads to degeneration of the hair cells in the Organ of Corti (1). In two of our three patients, initially a decompression illness was suspected, and they were referred to our Center for that reason. The dive profile and the long apparition delay precluded this diagnosis. Inner ear barotrauma could not formally be excluded; however, the presentation delay, the absence of any signs of middle ear barotrauma, and the absence of vestibular symptoms, made this diagnosis unlikely (4). In our third patient (case 2), no signs of increased haemolysis nor increased red blood cell adhesion could be documented. Sudden hearing loss has not been described as a possible complication of congenital spherocytosis. Viral etiology was not formally excluded in these three patients; however, it would appear to have been of little benefit in the management of their sudden deafness, and more of an academical value. Hyperbaric Oxygen Therapy: Although many different therapeutic protocols have been proposed, placebo-controlled dubbel-blind studies have not yet been able to prove the efficacy of any drug treatment over placebo (2, 5). Spontaneous recovery percentages of as much as 68% have been described (13). Although case reports of spectacular response to various drug treatments have been published after long treatment delays, a good recovery is considered rare if high hearing tresholds persists after the 7th day (6). HBOT is not as widely used as other therapeuticals measures. Reasons for this include lack of disponibility of hyperbaric chambers, a perception by ENT specialists of HBOT being an aggressive and dangerous therapy, and perhaps a lack of clinical and experimental papers on the subject, published in ENT scientific journals. Where HBOT is used, it is generally felt - as with any treatment - that the sooner this treatment is begun, the better the chances of recovery. A reduction of cochlear blood flow but at the same time an important rise of the endo-lymphatic oxygen pressure have both been well documented (5), and this could break a vicious circle of hypoxia-induced ultra-structural changes before reaching the "point of no return" where cellular death is inevitable. Spontaneous recovery: The problem with all studies on the treatment of sudden deafness is the inability to account for spontaneous recovery rates. Byl (1984) (6) analysed data from 225 cases of sudden deafness and developed a prognostic table, taking into account recognized prognostic factors such as severity of hearing loss, time to treatment, age, slope of audiometry curve, vertigo, hearing loss in the opposite ear, erythrocyte sedimentation rate. Following this (highly estimative) prognostic table, our patients had a chance of recovery of 15%, 15% and 30% respectively. Yamamoto et al. (1994) (7), found the recovery rate on the 7th day of treatment the most useful parameter for predicting the final recovery. Our three patients scored extremely bad, since none had a recovery of more than +10 dBa on day +7. Although we can not exclude a spontaneous recovery, the spectacular fall of the hearing treshold shortly after starting HBOT could not but be noted. In these patients, a sub-critical ischemia of the Organ of Corti's sensorineural elements may have been present, causing the hair cells to reside in a "dormant" state. The mechanisms by which HBOT restored almost normal hearing, are probably mainly related to edema-resolution, oxygen supplementation helping to "bridge the gap" in the meantime. An interesting observation could be made in case 2. Congenital spherocytosis (CS) has on several occasions been considered an absolute contra-indication for HBOT (8, 9). Because of a lack of solid data on this subject, we chose to treat our patient anyway, providing a close monitoring of hematological parameters. We have observed not the slightest sign of hemolysis, and therefore believe that the contra-indication should be relativized or even lifted in the case of asymptomatic, splenectomized CS patients. Conclusion Unfortunately, to this day, there is no reliable method for determining if the hair cells in the Organ of Corti are actually dead or dormant. Evoked oto-acoustic emissions might be clinically applicable in appreciating the chances of recovery (10); however, we are far from able to determine which patients should not be treated aggressively because of high chances of favorable outcome. This report is another illustration of the clinical observation that HBOT, either alone or in combination with other therapies, is an effective treatment in certain patients. Large series (1, 11, 12) have yielded a treatment success rate that is comparable to that of any other treatment, perhaps with less side effects. Even if HBOT is not considered as a primary treatment, it is clear that; as long as no reliable determination is possible of the patients who might not benefit from HBOT, a therapeutic trial is warranted in all patients who have not sufficiently responded to "standard" therapy. HBOT is, like any other treatment used, by no means 100% effective. It should however, in our opinion, not be delayed until little hope exists for further recovery.
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