If the patient already has unilateral deafness because of congenital reasons, mumps, LVAS, or any other reasons, how could we differentiate labyrinthitis from neuritis in the hearing loss side?
Are you asking for an explanation for recent increased deafness in an ear with long standing congenital deafness? My guess would be endolymphatic hydrops. Actually, I am not sure what labyrinthitis in general is other than a diagnosis of exclusion. I suspect any such case to be most like undiagnosed hydrops.
clinically with Hx of unilateral HL, tinnitus and vertigo with prior Hx of URTI or meningitis or congenital ear disease
i agree with both, if we understand the question; check delayed endolymphatic hydrops (DEH) of the ipsilateral form, decades after a sudden hearing loss (fibrosis, secondary hydrops...); there is a contra lateral form with hearing fluctuations in the normal hearing ear. See Schuknecht for old but imperial work.