Complex forms of benign paroxysmal positional vertigo

Benign paroxymal positional vertigo (BPPV) is the most common cause of peripheral vertigo and its lifetime incidence in general population is estimated around 10%. Such disease is due to dislodged otoconia that move from utricle into semicircular canals (SCC). Changes of the head position with relation to gravitational vector, make otoconia movement. As consequence the endolymphatic flow provokes cupula flexion and elicitation of a "positional" nystagmus (pNy). The different characteristics of positional nystagmus are based on the SCC involved and, in detail, on different portion of SCC (ampullary arm, non-ampullary arm or cupula) where otoconia position themselves. There are precise clinical features essential for the definition of pNy and they include latency, direction, time course and duration. Most of the times BPPV shows typical characteristics during diagnostic manoeuvres, whereas, sometimes, it presents different nystagmus patterns and represent challenging scenarios for clinicians. For example, an apogeotropic variant of pNy is attributed to presence of otoconia attached to the cupula (cupulolithiasis) of the HSC, or free floating otoconia of the ampullary arm of the HSC. In other complex forms of BPPV we can assist to a paradoxical direction changing pNy that may be due to a canal switch or to the re-entry of otoliths into canals. Other findings are pNy patterns due to a multicanalar involvement or, furthermore, an atypical manifestation is a positional downbeating nystagmus or a direction-fixed positional nystagmus. Another atypical scenario is represented by BPPV without pNy and we refer to this condition as "subjective BPPV. " In this chapter we will discuss the complex forms of BPPV in order to help clinicians to correctly diagnose and treat such particular conditions.