Abstract

Background
and Objectives: Secondary phase of nystagmus with late-reversal response, occurring with both caloric and rotational-induced nystagmus, is a well-recognized phenomenon. However, there have been few reports on late-reversal pattern of positional nystagmus in benign positional nystagmus (BPV). Furthermore, to our knowledge, there has been no prior report in Korea. To describe the strong secondary reversal nystagmus of BPV with various canal variants. Materials and Method: We analyzed the profiles of positional nystagmus in 8 patients with episodic vertigo and various type of BPV. Six patients had a canalolithiasis of the horizontal canal BPV. The 2 patients had a posterior canal BPV and the remaining 1 had a cupulolithiasis of the horizontal canal BPV.
Results
Regardless of patterns of the canal involvement, all patients showed strong secondary reversal nystagmus with magnitude of slow -phase velocity (SPV) is greater than 10°/sec. In horizontal canal variants, the reversal pattern of positional nystagmus is seen when the head is only rotated toward the affected ear in supine position and is occurred if the SPV of the initial response exceed 100°/sec. In posterior canal variant, nystagmus inversion is only seen in vertical component with from upbeats to downbeats.
Conclusion
This secondary phase of positional nystagmus with late-reversal response in BPPV may be explained by central adaptation or by reversal of the cupular movement direction due to gravitational forces.