This observation appears to apply to both SSD and AHL. We hypothesize that the longstanding auditory deprivation associated with profound unilateral hearing loss (UHL) could lead to a central adaptation process, contributing to the loss of lateralization of the Weber tuning fork test. Statistical analysis was performed using JMP 15 Software (Statistical Analysis Systems “SAS” Institute, Cary, NC, USA). SSD was defined by contralateral a PTA four-frequency average threshold below or equal to 30 dB, while AHL was defined by a PTA four-frequency average threshold above 30dB. According to the status of the contralateral ear, the patients were divided into single-sided deafness (SSD) or asymmetric hearing loss (AHL) groups. To meet the inclusion criteria, the patients had to have an audiometric interaural asymmetry of at least 50 dB at the frequency of the tuning fork tone (512 kHz). The Weber tuning fork test was performed using a standard 512 Hz tuning fork for all patients. The pure tone threshold average was considered the average threshold at four frequencies: 0.5, 1, 2, and 4 kHz. Profound hearing loss was defined by a pure tone threshold average of 90 dB or higher, as described previously. Pure tone audiograms (PTA) determined the ipsilateral and contralateral hearing status. The analysis involved the retrospective review of the hospital records and audiograms of adult patients with profound unilateral hearing loss (UHL) of at least ten years’ duration who presented to our outpatient department and/or auditory implant clinic between 20. The study was approved by the ethics committee of Charité Medical University (approval number EA1/015/21). These patients had different lateralization patterns on the Weber tuning fork test, seemingly related to the age of onset of deafness. This article reports on thirteen cases of patients with longstanding unilateral profound hearing loss of various etiologies. To date, there is no explanation as to why some patients with longstanding single-sided deafness lateralize and others do not. The observation that some patients with longstanding unilateral deafness fail to lateralize on the Weber test has been previously mentioned in the literature but remains poorly understood. In the case of unilateral sensorineural hearing loss, the intercochlear intensity and phase differences lead to vibrations being perceived louder in the contralateral unaffected ear, producing sound lateralization. Clinical and animal experiments have shown that bone conduction stimulates the cochlea mainly through two routes: (1) through the vibration of the middle ear ossicles and (2) vibrations of the skull itself (mainly of the cerebrospinal fluid). The mechanism of sound lateralization of the Weber test has intrigued hearing health professionals for many decades. In patients with conductive hearing loss, the sound should typically lateralize to the affected side, whereas in sensorineural hearing loss, it lateralizes to the contralateral side. The Weber tuning fork test has been mainly used in patients with unilateral hearing loss to distinguish between sensorineural and conductive hearing loss. Tuning fork tests have remained a mainstay of otologic examination for over a century. The findings may suggest a role for the Weber test as a simple, quick, and economical tool for screening poor cochlear implant candidates, thus potentially supporting the decision-making and counseling of patients with longstanding single-sided deafness. This notion may partially explain the poor outcome of adult cochlear implantation in longstanding single-sided deafness. The findings may imply a central adaptation process due to chronic unilateral auditory deprivation starting before the critical period of auditory maturation. In this patient cohort, childhood-onset unilateral profound hearing loss was significantly associated with the lack of lateralization of the Weber tuning fork test (Fisher’s exact test, p < 0.05) and the absence of tinnitus in the affected ear (Fisher’s exact test, p < 0.001). In the present study, we conducted a retrospective analysis of the medical records of patients with unilateral profound hearing loss (single-sided deafness or asymmetric hearing loss) for at least ten years. The observation that the Weber test does not lateralize in some patients with longstanding unilateral deafness has been previously described but remains poorly understood. Sound should typically lateralize to the contralateral side in unilateral sensorineural hearing loss. The Weber tuning fork test is a standard otologic examination tool in patients with unilateral hearing loss.
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