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Treatment outcomes for idiopathic sudden sensorineural hearing loss in dialysis patients – Scientific Reports

The results of our study indicate that the treatment outcomes for ISSNHL were poorer in the dialysis group than in the non-dialysis group. This study was the first to confirm a statistically significant difference in treatment outcomes between these two groups, even after adjusting for demographic factors and potential confounding variables that could influence treatment responses.

Although the precise incidence of SSNHL in patients undergoing dialysis remains unknown, Charlene et al. reported a 1.57 times higher incidence of SSNHL in patients with CKD than in controls without CKD14. However, limited number of reports on SSNHL in patients undergoing dialysis are available, and the relationship between dialysis and SSNHL remains unclear. Glucocorticoids have traditionally been the mainstay treatment option for ISSNHL, and current studies have suggested that the efficacy and safety of IT steroid injections are comparable to those of systemic steroid treatment2,15,16,17,18,19. Therefore, IT steroid injection is emerging as an alternative therapy for patients with systemic conditions, such as diabetes, hypertension, or CKD, which may pose challenges for the administration of systemic steroids. In our study, a higher proportion of patients undergoing dialysis received IT steroid injections compared to patients not undergoing dialysis, as patients undergoing dialysis were more likely to have underlying medical conditions. Owing to the between-group disparity in baseline characteristics, PSM was used to adjust for treatment strategies (Table 1), and neither systemic nor IT steroid treatment was associated with severe adverse effects.

Several published studies have suggested that the rate of CR or PR in the treatment of SSNHL in the general population ranges from 60 to 73%2,10,11,12. However, there is conflicting evidence regarding whether the treatment outcomes of SSNHL are poorer in patients undergoing dialysis than in patients not undergoing dialysis. Kang et al. reported a 36.4% rate of CR or PR to treatment for SSNHL in patients undergoing dialysis 2 months after steroid treatment. These results indicate that the treatment outcomes for these patients are inferior to those observed for the general population2,11,13. On the other hand, some studies have suggested that HD is not associated with a poor prognosis of treatment for SSNHL. Wang et al.19 reported on 32 patients undergoing HD derived from case studies and found that 16 (50.1%) had achieved complete or partial recovery, while nine (28.1%) had not recovered. However, in their cases, the initial hearing threshold was relatively lower and the age group was considerably younger compared to those in other studies, which likely contributed to their favorable outcomes. In a similar study conducted by Yamamoto et al.20, no statistically significant differences were observed in the pretreatment hearing level and recovery of the affected ear between the HD and non-HD groups (P = 0.12). However, a limitation of this study was the inclusion of a higher number of patients with diabetes compared to those included in the control group, which could have potentially acted as a confounding variable21. Furthermore, their study had a relatively smaller sample size, consisting of 23 patients undergoing dialysis and 101 patients not undergoing dialysis, compared to our study.

Hence, previous research did not consider the impact of underlying diseases, initial hearing threshold, duration of treatment delay, or differences in initial treatment methods, all of which could potentially influence treatment outcomes22,23,24. To address these concerns, our study used PSM to adjust for confounding variables. Moreover, a retrospective review of medical records spanning 15 years allowed for a relatively larger sample size compared to those in previous studies. Consequently, our findings revealed that 2 months after steroid treatment, 23.4% (11 out of 47) of patients in the dialysis group had achieved CR or PR, which was significantly lower than the 42.1% (99 of 235) in the non-dialysis group.

Although the exact mechanism underlying the development of SSNHL remains unknown, the kidney and cochlea exhibit numerous structural similarities. Both the stria vascularis of the cochlea and the glomerulus are epithelial tissues closely associated with the vascular system. Furthermore, the presence of a sodium–potassium-ATPase pump in the kidney and a carbonic-anhydrase enzyme in the cochlea have been implicated in maintaining body fluid homeostasis25,26. Moreover, the inner ear solely relies on the labyrinthine artery for its blood supply, which renders it susceptible to ischemic events because of its delicate vasculature27. Various factors, including uremia, ototoxic medication, electrolyte imbalances, and HD treatment, have been associated with hearing disorders in patients with kidney failure7,28. These factors suggest a shared impact of medication on these organs and strongly support the existence of a connection between hearing disorders and CKD.

In our study, we found that dialysis was associated with a poorer prognosis of treatment for SSNHL. In the PS-matched analysis, the treatment outcomes were significantly poorer in the dialysis group than in the non-dialysis group, and these findings were consistent when evaluating the average PTA values. These results indicate that dialysis itself may have an impact on the prognosis of treatment for ISSNHL.

There are several explanations for the inferior treatment outcomes for SSNHL in patients undergoing dialysis compared to patients not undergoing dialysis, although the precise mechanism remains undetermined. Firstly, patients undergoing dialysis often have multiple comorbidities, such as diabetes and hypertension, which are known contributors to the development of SSNHL29,30. These medical conditions can also pose challenges and reduce the efficacy of hearing treatment. Secondly, patients undergoing dialysis have a higher incidence of vascular calcification, which can lead to impaired blood flow to the inner ear and potentially contribute to SSNHL31,32. Additionally, calcification can pose challenges when administering medications through the blood vessels, potentially reducing treatment efficacy. Furthermore, patients undergoing dialysis may have altered pharmacokinetics and pharmacodynamics, affecting the absorption, distribution, metabolism, and elimination of drugs used in the treatment of sudden hearing loss. This can result in lower drug concentrations or altered drug effects, leading to a suboptimal therapeutic response33,34. However, in our study, a relatively higher proportion of patients undergoing dialysis received IT steroid treatment because of underlying medical conditions. Therefore, we conducted a subgroup analysis within the PS-matched cohort to specifically investigate whether there were significant differences in treatment outcomes based on the chosen treatment strategy, particularly between the group that received IT steroid treatment, which is free from the influence of systemic pharmacodynamics, and the group that received systemic steroid treatment. The subgroup analysis revealed significant differences only among patients who received a combination of systemic and IT steroids. Nevertheless, acknowledge the limitations of this subgroup analysis is crucial. The small sample size of the dialysis patient group had a substantial impact on the statistical power, and the possibility of administering both systemic and IT steroid treatments to patients with initially high hearing thresholds may have negatively affected the perceived prognosis. Despite these limitations, the subgroup analysis consistently indicated a trend of poorer treatment outcomes in patients undergoing dialysis than in patients not undergoing dialysis across all three treatment strategies. The reason for their poorer treatment response compared to the non-dialysis group is believed to be related to irreversible inner ear damage in the dialysis patient group, likely arising from unresolved issues such as uremia, osmotic changes resulting from dialysis, or factors such as acute neuritis caused by ultrafiltration during dialysis8,9. These multiple factors likely interacted in a complex manner, contributing to the observed outcomes. Larger prospective studies are warranted to substantiate these findings.

As the results of our study suggest that dialysis may have an impact on the outcomes of ISSNHL, it may be necessary to consider more intensive and prompt initiation of treatment for patients undergoing dialysis. Nevertheless, our study has several limitations. Firstly, this was a retrospective study conducted at a single center, which may have limited the generalizability of the findings. Secondly, as Asan Medical Center is a tertiary medical care facility, many patients in our study were referred from local clinics after initial treatment failure, resulting in potential selection bias, as we excluded patients with inconsistent treatment protocols. Despite these limitations, our study sample was larger than those in previous studies and used PSM to control for confounding variables to minimize bias. The clinical implications of our findings for the understanding and management of patients with ISSNHL undergoing dialysis are significant. Nevertheless, future prospective studies with larger populations are warranted to validate our findings.

Although SSNHL poses a significant complication affecting the quality of life of patients undergoing dialysis, the limited clinical experience and research in this area make it difficult for nephrologists to determine the appropriate management strategies. While our study was not prospective, it included a relatively larger number of patients compared to previous studies and yielded reliable results after adjusting for confounding variables. In our analysis, we provided first confirmation of a statistically significant difference in the treatment outcomes for ISSNHL between dialysis and non-dialysis groups. This finding suggests that dialysis may serve as a poor prognostic factor in the treatment of ISSNHL. Consequently, both nephrologists and otolaryngologists must be aware of these unfavorable outcomes when managing ISSNHL in patients undergoing dialysis. Efforts toward early diagnosis and the prompt implementation of tailored treatment strategies upon diagnosis are crucial for improving the outcomes of ISSNHL in patients undergoing dialysis.