Bilateral Superior Semicircular Canal Dehiscence Presenting as Progressive Gait Instability in a Patient With Parkinsonism and Autoimmune Features.

Superior semicircular canal dehiscence (SSCD) is a vestibular disorder caused by a defect in the bony roof of the superior semicircular canal, resulting in a third mobile window in the inner ear. This structural abnormality alters vestibular and auditory processing, producing symptoms such as vertigo, imbalance, sound sensitivity, autophony, and oscillopsia. We describe a 65-year-old man with a longstanding diagnosis of atypical Parkinsonism who presented with progressive gait apraxia, disequilibrium, and cognitive slowing. Despite undergoing bilateral deep brain stimulation (DBS) for tremor, his axial symptoms worsened. High-resolution computed tomography (CT) imaging later revealed bilateral SSCD. The patient reported subjective improvement during short courses of corticosteroids prescribed for unrelated autoimmune conditions. While objective physiological testing and lab markers were not available, the case underscores the risks of diagnostic overshadowing in neurodegenerative conditions and emphasizes the importance of identifying concurrent, potentially treatable vestibular pathology.