A case of superior semicircular canal dehiscence syndrome with functional convergence spasms

• Published in: Equilibrium Research Vol. 78; no. 3; pp. 178 - 184
• Main Authors: Watanabe, Chihiro, Owada, Satoko, Ito, Tsukasa, Murakami, Shingo, Kakehata, Seiji
• Format: Journal Article
• Language: Japanese
• Published: Kyoto Japan Society for Equilibrium Research 30.06.2019; Japan Science and Technology Agency
• Subjects: Cochlea; Convergence; convergence spasm; Dehiscence; Ear canal; Middle ear; middle fossa approach; Nystagmus; Semicircular canals; sono-ocular test; Surgery; third window; Vertigo; Vestibular system
• ISSN: 0385-5716; 1882-577X
• DOI: 10.3757/jser.78.178

Herein, we present a patient with superior semicircular canal dehiscence syndrome (SCDS) manifesting as convergence spasms, which were alleviated by canal plugging surgery. SCDS is described in the literature by Minor as “a condition characterized by vertigo and oscillopsia induced by loud sounds or changes in the pressure of the external auditory canal or middle ear due to the dehiscence of the bone overlying the superior semicircular canal.” Convergence spasms are characterized by intermittent sustained convergence, accommodative spasms and miosis, and are likely to be caused by a functional disease, although in some cases, it is a manifestation of an organic disease.　A 49-year-old male patient visited our department with a 2-year history of intermittent sudden vertigo and cloudy vision. The vertigo attacks had gradually increased in frequency and could last all day. Pure-tone audiometry showed bilateral conductive hearing impairment with air-bone gap at low frequencies from 125Hz to 500Hz. A head CT showed bone dehiscence above the bilateral superior semicircular canals and tegmen of the epitympani.　Initial equilibrium testing did not reveal any abnormal findings. Initial sono-ocular testing of the right ear indicated upbeat nystagmus. However, after multiple outpatient visits, the upbeat nystagmus disappeared during the sono-ocular test and was replaced by paradoxical convergence. The eye tracking test also revealed paradoxical convergence, which became frequent and was accompanied by pupillary miosis. This paradoxical convergence was ultimately diagnosed as convergence spasms.　No improvement of symptoms was achieved through non-surgical treatments over an extended period of time, therefore, canal plugging surgery was recommended. The surgery was performed through a middle fossa approach, and it completely eliminated the cochlear and vestibular symptoms associated with SCDS and the convergence spasms. Finally, we suspected that the convergence spasms were caused by ocular dysfunction as well as neurological factors related to the SCDS.