How do I differentiate peripheral from central vestibular disease in a geriatric dog and what is expected recovery?

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Neurological examination correctly identifies central vestibular disease in 98.4% of dogs but misclassifies peripheral disease as central in 22.6% of cases, making MRI essential when a dog with apparent peripheral signs fails to improve promptly.7 The key differentiating signs on neurological examination are those indicating central involvement. Central vestibular disease is characterized by proprioceptive deficits, altered mentation, cranial nerve deficits other than CN VII or VIII, and vertical or dysconjugate nystagmus.4 Peripheral vestibular disease produces head tilt, ataxia, nystagmus (typically horizontal or rotary), positional strabismus, and — when the lesion is at the level of the petrous temporal bone — concurrent ipsilateral CN VII deficits and Horner syndrome.15 Approximately 20% of dogs with a suspected peripheral neurolocalization on examination are subsequently found to have intracranial disease on MRI, reinforcing that examination alone is insufficient for definitive localization.2 A modified penlight-cover test can add bedside support for peripheral localization. Removing visual input by shining a penlight into one eye while covering the other increases nystagmus beat frequency in 33% and slow phase velocity in 24% of dogs with confirmed peripheral lesions, while only 1 of 16 dogs with central lesions showed any increase in beat frequency and none showed increased slow phase velocity.2 A positive result (increased beat frequency or slow phase velocity) raises suspicion for peripheral disease when interpreted alongside the full neurological examination.2 In geriatric dogs, idiopathic vestibular syndrome (IVS) is the most likely diagnosis, followed by otitis media/interna and, less commonly, hypothyroidism, neoplasia, and cholesteatoma.1 Increasing age is associated with a diagnosis of IVS rather than otitis media/interna.1 The prevalence of vestibular disease in dogs aged 9 years or older reaches 0.36% in primary care, compared with 0.08% overall.11