Melanin in human vestibular organs: what do we know now? An ultrastructural study and review of the literature

Hearing impairment in patients with alopecia areata

Background Alopecia areata is an autoimmune disease that damages hair follicles and follicular melanocytes can be involved in the autoimmune process. Therefore, similar to vitiligo, there may be a relationship between sensorineural hearing loss and alopecia areata. Aims/objectives This study aimed to investigate potential hearing impairments in patients with alopecia areata. Methods A total of 42 subjects with alopecia areata and 42 healthy individuals enrolled in this cross-sectional study. The hearing was evaluated by vestibular evoked myogenic potential, otoacoustic emission and pure tone audiometry tests in the patients and control subjects. Results A normal otoacoustic emission was reported in 59.5% and 100% of subjects with alopecia areata and the controls, respectively (P = 0.02). Higher speech recognition thresholds (P = 0.02) and speech discrimination scores were reported more in subjects with alopecia areata than in controls (P < 0.001); however, the most comfortable level of speech was not significantly different between the groups (P = 0.06). The greatest increase in the hearing threshold was recorded at a frequency of 8000 Hz, while at frequencies of 500 and 1000 Hz, the patients and controls did not significantly differ (P > 0.05). About 6 (14.3%) and 2 (4.8%) of patients with unilateral and bilateral involvement, respectively, demonstrated no vestibular evoked myogenic potential response in the alopecia areata group. The patients and controls did not significantly differ in terms of amplitudes of the vestibular evoked myogenic potential test (P = 0.097). Limitation Small sample size and qualitative measurement of otoacoustic emission were limitations of our study. Conclusion Hearing loss was more common in alopecia areata patients than in healthy individuals. Follicular melanocytes may be involved in the alopecia areata inflammatory process, and destroying melanocytes may impact hearing function in the inner ear. However, there was no significant relationship between the duration and severity of alopecia areata and hearing loss.

Beyond skin white spots: Vitiligo and associated comorbidities

Vitiligo is a common depigmentation disorder of an unknown origin characterized by the selective loss of melanocytes, resulting in typical white macules and patches. However, vitiligo is now recognized as more than just a skin disease, what a dermatologist observes as a white spot of skin is just the "tip of the iceberg" of the condition. We attempt to clarify the classification of comorbidities associated with vitiligo from various reviews and reports, and describe their possible pathogenesis. In conclusion, the literature provides evidence of an association between vitiligo and ocular and auditory abnormalities, autoimmune disorders, other dermatological diseases, metabolic syndrome and related disorders, and psychological diseases. These associations highlight the importance of a multidisciplinary approach in managing vitiligo patients.

Association of vitiligo with high-frequency sensorineural hearing loss: a systematic review and meta-analysis

The association between vitiligo and hearing loss has been noted but the specific frequencies and degrees of hearing impairment remain unclear. The objective of this systematic review was to investigate the relationship between vitiligo and hearing thresholds at various specific frequencies. We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. We searched MEDLINE and Embase for relevant studies from inception to 10th April 2021. Case-control studies, cross-sectional, or cohort studies that compared the frequency-specific hearing thresholds between vitiligo patients and age-matched non-vitiligo controls were included. There were neither language nor geographic limitations. We used the Newcastle-Ottawa Scale to assess the risk of bias of included studies. The DerSimonian and Laird random-effects model was utilized in meta-analyses due to expected clinical heterogeneity. We included 9 case-control studies with 371 vitiligo patients and 349 controls, which were rated with low or unclear risk. We found neither relevant cross-sectional nor cohort studies. The meta-analysis showed that when compared with controls, vitiligo patients had significantly higher pure-tone hearing thresholds at 2000, 4000, and 8000 Hz. In conclusions, vitiligo patients are prone to high-frequency sensorineural hearing loss.

Migration and fate of vestibular melanocytes during the development of the human inner ear

Melanocytes are present in various parts of the inner ear, including the stria vascularis in the cochlea and the dark cell areas in the vestibular organs, where they contribute to endolymph homeostasis. Developmental studies describing the distribution of vestibular melanocytes are scarce, especially in humans. In this study, we investigated the distribution and maturation of the vestibular melanocytes in relation to the developing dark cell epithelium in inner ear specimens from week 5 to week 14 of development and in surgical specimens of the adult ampulla. Vestibular melanocytes were located around the utricle and the ampullae of the semicircular canals before week 7 and were first seen underneath the transitional zones and dark cell areas between week 8 and week 10. At week 10, melanocytes made intimate contact with epithelial cells, interrupting the local basement membrane with their dendritic processes. At week 11, most melanocytes were positioned under the dark cell epithelia. No melanocytes were seen around or in the saccule during all investigated developmental stages. The dark cell areas gradually matured and showed an adult immunohistochemical profile of the characteristic ion transporter protein Na⁺/K⁺‐ATPase α1 by week 14. Furthermore, we investigated the expression of the migration‐related proteins ECAD, PCAD, KIT, and KITLG in melanocytes and dark cell epithelium. This is the first study to describe the spatiotemporal distribution of vestibular melanocytes during the human development and thereby contributes to understanding normal vestibular function and pathophysiological mechanisms underlying vestibular disorders.