In what direction should catch-up nystagmus be relative to the affected ear in a patient with a peripheral vestibular disorder?

Direction of Catch-up Nystagmus in Peripheral Vestibular Disorders

In peripheral vestibular disorders, catch-up nystagmus direction depends on the type of BPPV, with geotropic nystagmus beating away from the affected ear and apogeotropic nystagmus beating toward the affected ear during lying-down testing. 1

Types of Nystagmus in Peripheral Vestibular Disorders

Lateral Canal BPPV Nystagmus Patterns

The direction of nystagmus in lateral canal BPPV follows specific patterns that help identify the affected ear:

• Geotropic Lateral Canal BPPV:

  • During lying-down test: Nystagmus beats away from the affected ear 1, 2
  • During supine roll test: Stronger nystagmus when affected ear is down 1
  • During head pitch test: Nystagmus usually beats toward the affected ear 1

• Apogeotropic Lateral Canal BPPV:

  • During lying-down test: Nystagmus beats toward the affected ear 1, 2
  • During supine roll test: Stronger nystagmus when unaffected ear is down 1
  • During head pitch test: Nystagmus beats away from the affected ear 1

Diagnostic Methods to Determine the Affected Ear

The accurate identification of the affected ear is crucial for proper treatment of BPPV. Several testing methods can be used:

1. Supine Roll Test (most common method):

   • Geotropic form: The side with strongest nystagmus is the affected ear
   • Apogeotropic form: The side opposite the strongest nystagmus is the affected ear 1

2. Lying-Down Test (sitting to supine):

   • Geotropic: Nystagmus beats away from affected ear
   • Apogeotropic: Nystagmus beats toward affected ear 1, 2

3. Head Pitch Test (in supine position, sitting up with head bent down):

   • Geotropic: Nystagmus usually beats toward affected ear
   • Apogeotropic: Nystagmus beats away from affected ear 1

4. Bow and Lean Test:

   • Geotropic:
     • Bowing (face down): Nystagmus beats toward affected ear
     • Leaning (face up): Nystagmus beats away from affected ear
   • Apogeotropic:
     • Bowing (face down): Nystagmus beats away from affected ear
     • Leaning (face up): Nystagmus beats toward affected ear 1

Clinical Pearls and Pitfalls

• In approximately 20% of lateral canal BPPV cases, clear lateralization remains difficult to determine even with multiple testing methods 1

• When lateralization is unclear, clinicians may need to treat one side and then the other 1

• The temporal profile of nystagmus helps differentiate between canalolithiasis and cupulolithiasis:

  • Canalolithiasis (geotropic): Paroxysmal nystagmus that peaks at 5-20 seconds and declines to near zero by 60 seconds 3
  • Cupulolithiasis (apogeotropic): More persistent nystagmus that maintains significant intensity even at 40 seconds 3

• Be aware that posterior canal BPPV can transition to lateral canal BPPV during treatment maneuvers (canal switch) 4

• Always distinguish BPPV from other causes of vertigo such as vestibular neuritis, Ménière's disease, vestibular migraine, and central causes 1, 4

Algorithmic Approach to Determining the Affected Ear

1. Perform supine roll test to determine if nystagmus is geotropic or apogeotropic
2. Assess which side produces stronger nystagmus during the supine roll test
3. Confirm with lying-down test (sitting to supine)
4. If results are still unclear, use head pitch test or bow and lean test
5. When multiple tests yield conflicting results, treat the side most consistently indicated

Remember that proper identification of the affected ear and type of BPPV is essential for selecting the appropriate repositioning maneuver, which directly impacts patient outcomes and quality of life.