Table I.

Definitions of MD

Definition	Symptoms
Definite MD	≥ 2 definitive spontaneous episodes of vertigo, each lasting 20 minutes to 12 hours Audiometrically documented low- to medium-frequency sensorineural hearing loss in one ear, defining the affected ear on at least one occasion before, during or after one of the episodes of vertigo Fluctuating aural symptoms (hearing, tinnitus or aural fullness) in the affected ear Not better accounted for by another vestibular diagnosis.
Probable MD	Two or more episodes of vertigo or dizziness, each lasting 20 minutes to 24 hours Fluctuating aural symptoms (hearing, tinnitus or aural fullness) in the affected ear Not better accounted for by another vestibular diagnosis