Audiovestibular disorders as autoimmune reaction in patients with melanoma.

Melanoma is an aggressive form of cancer derived from neuroectodermal melanocytes. Melanocytes are present in the skin and hair follicles, as well as in the eye (iris and choroids), the leptomeninges, the anal canal and the inner ear. In the inner ear melanocytes are found both in the intermediate layer of the stria vascularis of the cochlea and in the dark cells of the vestibular organs. They are believed to play an important role in the production of endolymphatic potentials and in the maintenance of normal volumes of the inner ear fluids. Recently, audiovestibular dysfunctions have been demonstrated in patients treated with immunotherapy for metastatic melanoma and have been related to an autoimmune attack on the normal melanocytes of the inner ear. Melanoma is an immunogenic tumor type frequently associated with spontaneous autoimmune manifestations which seem to be associated with better prognosis. The melanoma-associated antigens are also expressed in normal melanocytes in the skin, eye and ear. We hypothesize that inner ear melanocytes could be a target of an autoimmune process in patients affected by melanoma. The immune system could produce antibodies that cross-react with both the melanoma cells and the labyrinth melanocytes causing an altered homeostasis of endolymphatic liquids and provoking some labyrinthic disorders such as vertigo, hearing loss, aural fullness and tinnitus resembling or influencing Ménière's disease. In this perspective, audiovestibular disorders could be interpreted as an attempt by the individual immune system to develop anti-tumor response. In patients affected by melanoma an autoimmune genesis has already been advocated for ocular symptoms in melanoma-associated retinopathy, where the cross-reaction happens against retinal cells. A possible role of inner ear melanocytes should be considered as a potential cause of audiovestibular disorders. Further research is needed to demonstrate a connection between melanoma and labyrinth dysfunctions such as in melanoma-associated retinopathy.

Effect of eye lateralization on contralateral suppression of transient evoked otoacoustic emissions.

Several studies have previously demonstrated that postural changes modify evoked otoacoustic emission. In order to evaluate a possible interaction between eye muscles and ciliated cells in the inner ear, we studied the effects of eye lateralization on the contralateral suppression of transient evoked otoacoustic emissions (TEOAEs). Thirty-eight normal hearing subjects with TEOAEs were recruited. Their TEAOEs at threshold level were recorded with contralateral suppression (white noise) via straight ahead fixation and right or left lateral fixation. Eye lateralization in the same direction of the white noise significantly decreased the suppression at 4 kHz (p = 0.003). The signal-to-noise ratio in the suppression condition with straight ahead was 1.54 (± 4.610) dB, while the ratio was 3.48 (± 4.631) dB in the suppression condition with gaze toward the white noise. Eye lateralization seems to reduce the contralateral suppression effect of TEOAEs at 4 kHz. However, further studies are necessary to investigate the possible mechanisms of this phenomenon.