Why is the nystagmus in Benign Paroxysmal Positional Vertigo (BPPV) fatigue able to resolve?

From the Guidelines

The nystagmus in Benign Paroxysmal Positional Vertigo (BPPV) is fatiguable because of the temporary nature of the mechanical stimulation that causes it, as supported by the most recent clinical practice guideline update in 2017 1.

Key Points

• The temporary nature of the mechanical stimulation is due to the movement of displaced calcium carbonate crystals (otoconia) in the semicircular canals, which stimulate the hair cells and create an inappropriate signal of movement.
• When a person with BPPV moves their head into a triggering position, the otoconia move and stimulate the hair cells, causing intense vertigo and the characteristic nystagmus.
• If the position is maintained, the otoconia settle into a stable position and stop moving, which causes the nystagmus to diminish or disappear entirely, typically within 30-60 seconds.
• This fatiguability is a key diagnostic feature of BPPV that distinguishes it from central causes of positional vertigo, as noted in the clinical practice guideline update in 2017 1.

Diagnostic Considerations

• The Dix-Hallpike test is used to diagnose posterior semicircular canal BPPV, and the supine roll test is used to diagnose lateral semicircular canal BPPV, as recommended in the clinical practice guideline update in 2017 1.
• The nystagmus response becomes progressively weaker with each repetition of the Dix-Hallpike or other positioning tests as the otoconia become temporarily depleted or repositioned.
• This phenomenon occurs because the vestibular system adapts to the abnormal stimulation, and the brain begins to compensate for the false signals of movement, as explained in the clinical practice guideline update in 2017 1.

Treatment Implications

• The fatiguability of the nystagmus in BPPV is an important consideration in the treatment of the condition, as it can affect the outcome of canalith repositioning procedures (CRPs) and other treatments, as noted in the clinical practice guideline update in 2017 1.
• CRPs are the treatment of choice for initial BPPV treatment failures deemed to be due to persistent BPPV, and repeat canalith repositioning maneuvers can be performed as a preferred treatment, as recommended in the clinical practice guideline update in 2017 1.

From the Research

Nystagmus in BPPV Fatigue

The nystagmus in BPPV fatigue is able to be restored through certain maneuvers, as evidenced by the following points:

• A new maneuver was developed to rapidly restore positional nystagmus in cases of BPPV fatigue, facilitating accurate diagnosis of posterior canal-type BPPV 2.
• The Dix-Hallpike test, used for diagnosis of posterior-canal-type BPPV, can induce positional nystagmus, but this nystagmus typically becomes weaker when the test is repeated, a phenomenon known as BPPV fatigue 3.
• The effect of BPPV fatigue typically disappears within 30 minutes, at which point the Dix-Hallpike test again induces clear positional nystagmus 3.

Pathophysiology of BPPV

The pathophysiology of BPPV is characterized by:

• Canalolithiasis, where otoconial debris is detached from the otolithic membrane and floats freely within the endolymph of the canal 3, 4, 5.
• Cupulolithiasis, where the otoconial debris settles on the cupula of the semicircular canal and the specific gravity of the cupula is increased 3, 4, 5.

Diagnosis and Treatment of BPPV

The diagnosis and treatment of BPPV involve:

• The Dix-Hallpike test and supine roll test to induce positional nystagmus 3, 4, 5.
• The canalith repositioning procedure (CRP) to move otoconial debris from the affected semicircular canal to the utricle 3, 4, 5.
• The Epley maneuver and Gufoni maneuver as specific types of CRP for posterior-canal-type and lateral-canal-type BPPV, respectively 3.