Downbeat nystagmus (DBN) during the Dix-Hallpike test (DHT) suggests excitation of the anterior canal (AC) or inhibition of the posterior canal (PC) underlying benign paroxysmal positional vertigo (BPPV). This case series describes 2 individuals presenting with DBN in positional testing suggestive of a PC BPPV variant termed apogeotropic PC-BPPV and due to inhibition of the PC.
Case 1 illustrates a DBN during positional testing (PC inhibition) that changes to an upbeating nystagmus (PC excitation) representing the otoconial material changing location and direction of movement within the PC. Case 2 describes a canal jam in the nonampullary segment of the PC.
Apogeotropic PC-BPPV can cause DBN due to inhibition of the vestibular afferent. Apogeotropic PC-BPPV may be due to a canal jam of debris within the nonampullary segment or cupulolithiasis with debris attached to the inferior-most aspect of the cupula within the PC. It can be difficult to differentiate AC-BPPV from the apogeotropic PC-BPPV variant. In both forms, the affected canal may be provoked in 1 or both positions of the DHT and straight head hanging position. However, in AC-BPPV there may only be a slight or absent torsional component toward the involved ear. In apogeotropic PC-BPPV, a strong torsion away from the involved ear is typically observed. The straight head hanging position may resolve AC-BPPV or convert apogeotropic PC-BPPV to typical PC-BPPV.
These 2 cases illustrate atypical variants of BPPV that clinicians must consider in their interpretation of DBN during positional testing, particularly in the absence of other neurological signs.
Physical Therapy Program, Midwestern University, Downers Grove, Illinois.
Correspondence: Janet Odry Helminski, PT, PhD, Physical Therapy Program, Midwestern University, 555 31st St, Downers Grove, Illinois 60515 (email@example.com).
This work has previously been presented at the International Conference of Vestibular Rehabilitation: Translating Research to Advance Practice, sponsored by the Academy of Neurologic Physical Therapy, American Physical Therapy Association.
The author declares no conflict of interest.
Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal's Web site (www.jnpt.org).