Beat-to-Beat Nystagmus Differentiation Between Benign Paroxysmal Positional Vertigo (BPPV) and Vestibular Migraine (VM): A Cross-Sectional Videonystagmographic Study From Northern India.

Background Benign paroxysmal positional vertigo (BPPV) and vestibular migraine (VM) are among the most common causes of vertigo encountered in clinical practice. Both conditions can present with similar symptoms, such as dizziness and positional vertigo, yet their underlying mechanisms and management differ significantly. Misdiagnosis can lead to ineffective or inappropriate treatment. Objective This study aims to evaluate the characteristics of beat-to-beat positional nystagmus in patients with BPPV and VM using videonystagmography (VNG) and to identify distinguishing features of nystagmus that facilitate accurate diagnosis and treatment. Methods A cross-sectional observational study was conducted at a tertiary care center in Lucknow, India. Of 343 patients screened for positional vertigo, 110 patients who met the inclusion criteria were enrolled. Patients were divided into two groups based on clinical and diagnostic criteria: BPPV (n=57) and VM (n=53). All patients underwent a comprehensive vestibular assessment using VNG, with specific attention to slow-phase velocity (SPV), amplitude, direction, and duration of nystagmus during various positional tests. Statistical analysis was conducted using descriptive statistics and t-tests. Results The study revealed distinct differences in nystagmus characteristics between patients with BPPV and VM. Patients with BPPV demonstrated a characteristic crescendo-decrescendo pattern in SPV, indicating a mechanical etiology linked to canalith kinetics. In contrast, patients with VM showed a higher initial SPV with a more sustained, constant pattern of nystagmus, suggestive of central vestibular hyperexcitability. Peak nystagmus amplitude and SPV were significantly higher in BPPV (mean peak amplitude: 11.55° vs. 5.64°, p=0.02; mean peak SPV: 21.16°/s vs. 13.10°/s, p=0.005). Positional testing demonstrated distinct patterns between the two groups. The Dix-Hallpike (DH) and supine head-hanging (head extension) positions were more frequently positive in patients with BPPV, whereas the pitch-forward (head flexion) position more frequently elicited nystagmus in patients with VM. Conclusion VNG-based assessment of beat-to-beat nystagmus characteristics can be a supportive, objective method for differentiating BPPV from VM in difficult cases. Accurate differentiation is crucial for guiding appropriate therapeutic strategies, including repositioning maneuvers for BPPV and migraine prophylaxis for VM.