## **Core Concept**
Benign paroxysmal positional vertigo (BPPV) is a vestibular disorder arising from the inner ear, characterized by brief, intense episodes of vertigo triggered by specific head movements. It is associated with the abnormal movement of otoconia within the otolith organs of the inner ear, specifically the utricle and saccule. The Dix-Hallpike maneuver is a diagnostic test used to assess for BPPV.

## **Why the Correct Answer is Right**
The correct answer, **torsional nystagmus**, is a key finding that favors BPPV over central positional vertigo. In BPPV, the nystagmus is typically torsional (rotatory), with a latency of onset (usually 1-5 seconds), and it fatigues with repeated testing. This type of nystagmus is indicative of a peripheral vestibular lesion, such as BPPV. Central positional vertigo, on the other hand, often presents with a different type of nystagmus that does not have a latency period and does not fatigue.

## **Why Each Wrong Option is Incorrect**
- **Option A:** *No nystagmus* would not support the diagnosis of BPPV, as the presence of nystagmus, particularly torsional, is a hallmark of the condition.
- **Option B:** *Sustained nystagmus* is more characteristic of central vestibular disorders rather than BPPV. In central positional vertigo, the nystagmus is often not torsional and does not typically fatigue.
- **Option C:** *Vertical nystagmus* is concerning for a central cause of vertigo. While not exclusively indicative of central pathology, in the context of positional vertigo, it does not favor BPPV.

## **Clinical Pearl / High-Yield Fact**
A crucial clinical pearl for diagnosing BPPV is the use of the Dix-Hallpike maneuver and the Epley maneuver as both a diagnostic and therapeutic tool. The presence of torsional nystagmus with a short latency and duration that fatigues with repeated testing is highly suggestive of BPPV.

## **Correct Answer: D. Torsional nystagmus.**