Small Animal Dermatology, 3rd edition

CHAPTER 37 OTITIS EXTERNA, MEDIA, AND INTERNA 545

Hypersensitivity: atopy, cutaneous adverse reaction to food, contact allergy, and

systemic or local drug reaction; most common cause of chronic otitis externa;

present in over 50% of cases of cutaneous adverse reaction to food (Figure

37.15).

Foreign body: plant material, accumulation of hair, medication.

Keratinization disorder: increased cerumen production resulting in functional

obstruction of the canal.

Endocrinopathy: causes immunosuppression and changes in cerumen produc-

tion.

Autoimmune disease: frequently affects the pinnae and less often the external

ear canal.

 Secondary causes:
Bacterial infection:Staphylococcus pseudintermedius,Pseudomonas aeruginosa,

Enterococcusspp.,Proteus mirabilis,Streptococcusspp.,Corynebacteriumspp.,

andEscherichia coli

Pseudomonas aeruginosamost commonly cultured in otitis media

Fungal infection:Malassezia pachydermatis,Candida albicans, and rarely other

fungi (Sporothrix schenckii,Cryptococcus neoformans).

 Perpetuating causes:
Chronic changes: stenosis of the canal due to cerumen gland hyperplasia and

polyp formation, swelling from inflammation, scarring and calcification

Chronic change increases retention of debris in the ear by increased cerumen

production and decreased removal by epidermal migration and by physical

obstruction.

 Predisposing causes:
Obstruction: neoplasia, inflammatory polyp, cerumen gland hyperplasia, accu-

mulation of hair (Figures 37.16–37.19)

Ceruminous cystomatosis: multiple dark nodules on the concave portion of the

pinna and proximal horizontal canal of middle-aged cats (Figure 37.20).

 Otitis media:
Most often caused by descending otitis externa
May develop secondary to upper respiratory infection by ascension of infection

through the auditory tube or by hematogenous spread

Otitis media may perpetuate otitis externa

Patency of tympanic membrane may be difficult to assess; careful cleaning may

reveal a small defect (Figures 37.21, 37.22)

Primary secretory otitis media: associated with accumulation of mucoid viscous

exudate in the middle ear causing discomfort and intermittent otitis externa fol-

lowing rupture of the tympanic membrane; may be unilateral or bilateral; possi-

bly due to abnormality in the structure or function of the auditory tube; exudate

is often aseptic.

Otitis Interna

 Extension of infection from otitis externa/media.