Clinical spectrum of positional downbeat nystagmus: a diagnostic approach

Positional downbeat nystagmus (pDBN) is a common finding in dizzy patients, with etiologies ranging from benign paroxysmal positional vertigo (BPPV) to central vestibular lesions. Although peripheral pDBN often presents with distinct clinical features that differentiate it from BPPV, diagnosing its etiology can be challenging. A thorough clinical evaluation, including the physical characteristics of the nystagmus, response to positional maneuvers, and neurological findings, is often sufficient to diagnose conditions that provoke pDBN such as anterior canal BPPV, atypical posterior canal BPPV, and central causes. However, when the diagnosis remains uncertain, a brain MRI focusing on the posterior fossa is required. In human lesion models, the vestibulocerebellum (nodulus and uvula) is commonly implicated in pDBN. Central causes of positional vertigo include vascular events, tumors, immune mediated, toxicity, and demyelinating diseases. Ultimately, a significant number of cases will remain without a clear etiology despite extensive workup. Clinicians should be vigilant for signs suggesting central vestibular dysfunction at follow-up in cases of apparently refractory BPPV. The aim of this work is to provide a comprehensive overview of pDBN and offer a logical approach to its assessment, along with recommendations for future research directions.