Small Animal Dermatology, 3rd edition

546 DISEASES/DISORDERS

 Central vestibular disease: differentiated by brainstem signs such as stupor and

lethargy.

 Neoplasia: diagnosed by imaging studies.

 Endocrinopathy: polyneuropathy and Horner’s syndrome associated with hypothy-

roidism.

 Metronidazole toxicity.

 Thiamine deficiency (cats).

 Trauma.

 Idiopathic vestibular disease (older dogs and middle-aged cats): diagnosis made by

exclusion of other causes.

DIAGNOSTICS

 CBC/biochemistry/urinalysis: usually normal; may indicate a primary underlying dis-

ease (e.g., hypothyroidism, hematogenous spread of infection).

 Allergy testing: restricted-ingredient food trial for cutaneous adverse reaction to food;

intradermal and/or serum allergy testing for atopy.

 Neurologic examination: may indicate otitis interna.

 Direct otoscopy: visualization of the external canal, tympanic membrane, and dorsal

and middle portions of the bulla (if tympanum ruptured).

 Video-otoscopy:
Provides a magnified view of the canal
Improved visualization for diagnosis of otitis media
Permits more controlled sample collection
Allows direct visualization during cleaning, myringotomy, and surgical proce-

dures (including laser ablation and mass biopsy or removal) (Figure 37.23).

 Imaging:
Radiographs: not highly sensitive for diagnosis of otitis media; useful for eval-

uating chronic changes; bullae should appear thin-walled and air-filled; bullae

may appear cloudy if filled with exudate; stenosis of external ear canal; thicken-

ing of bullae and petrous temporal bones with mineralization; presence of bone

lysis with osteomyelitis or neoplastic disease

Ultrasound: poor sensitivity in detecting otitis media compared with CT, MRI or

video-otoscopy

CT or MRI:

Detailed evidence of fluid or tissue density (e.g., polyp) in the bulla, adja-

cent tissues, or auditory tube

CT: useful for bony changes; stenosis or calcification of the canals; contrast

used to differentiate debris from soft tissues

MRI: useful for evaluation of the tympanic membrane and soft tissues; help-

ful to differentiate central versus peripheral vestibular disease.

 Skin scrapings from pinnae: ectoparasites.

 Dermatohistopathology: autoimmune disease, neoplasia, cerumen gland hyperplasia;

pinnae difficult to biopsy; avoid damaging auricular cartilage.