[Inverted caloric nystagmus of perforated ears upon air caloric stimulation]

It is well known that inverted caloric nystagmus is seen during air caloric testing in cases of chronic otitis media. The mechanism of inversion and its clinical significance are discussed here. Temperature changes in the tympanic cavity and external ear canal were measured with a microthermister and a digital tester in seventeen ears with tympanic membrane perforation, during bithermal air caloric testing. The tympanic cavity mucosa was cooled by hot stimulation because of the evaporation of heat. When the perforation was closed or humidified air was used, the tympanic cavity mucosa was not cooled by hot stimulation and the inverted caloric nystagmus changed to a normal response. Inverted caloric nystagmus occurred in 30.4% of 335 ears affected by chronic otitis media with perforation. Inverted caloric nystagmus occurred in 90 ears with hot stimulation and in 12 ears with cold stimulation. Inverted caloric nystagmus turned to normal response after myringoplasty in all of 10 ears. The cooling effect caused by evaporation of water from the moist middle ear mucosa during dry air blowing and direct thermal conduction to the vestibulum through a perforation of the ear drum and inversion of the endolymphatic convection seemed to cause the inversion.