Vestibular hypersensitivity to sound - (Tullio phenomenon) - Structural and functional assessment

Objectives: To establish the role of high-resolution CT imaging and tests o f vestibulocollic reflexes in diagnosing and understanding the pathogenesis of the Tullio phenomenon. Background: The Tullio phenomenon is a syndrome in which acoustic stimulation produces symptoms and signs of vestibular act ivation. It has previously been associated with an abnormally low threshold for click-evoked vestibulocollic responses and also with dehiscence of the roof of the anterior (superior) semicircular canal on high-resolution CT s cans of the temporal bones. Methods: High-resolution CT scans of the tempor al bones and vestibulocollic responses in sternocleidomastoid to both click s and transmastoid galvanic stimulation (3 mA/2 msec) were studied in four patients with the Tullio phenomenon (one bilateral). Results: Click-evoked thresholds were low for all affected ears (four at 65 dB nHL, one at 55 dB nHL) and normal (>70 dB nHL) for the three unaffected ears. In contrast, ga lvanic-evoked vestibulocollic responses were symmetric and of normal size i n all patients. The bony roof of the anterior (superior) semicircular canal was thin, possibly absent, on CT of all affected ears and also in two out of three unaffected ears. Conclusions: The normal galvanic vestibulocollic responses indicate that sound sensitivity in patients with the Tullio pheno menon is likely to occur distal to the vestibular nerve, probably at the le vel of the receptors. Both click hypersensitivity and dehiscence of the ant erior (superior) semicircular canal are associated with the Tullio phenomen on but as the CT scan abnormality can occur in clinically unaffected ears, click testing is important for specific diagnosis. Abnormal sound sensitivi ty, as demonstrated by click responses, confirms that the radiologic abnorm ality is function significant.