Cytological and microbiological characteristics of middle ear effusions in brachycephalic dogs

Abstract

Background: Middle ear effusion is common in brachycephalic dogs with similarities to otitis media with effusion in children. Association with the cranial and eustachian tube morphology and bacterial infection is suspected in both species.

Hypothesis/objectives: To determine cytological and bacteriological features of middle ear effusions in dogs, provide information on histological features, and further assess the dog as a model of the human disease.

Animals: Sixteen live dogs, 3 postmortem cases of middle ear effusion, and 2 postmortem controls.

Methods: Prospective; clinical investigation using computed tomography, magnetic resonance imaging, video-otoscopy, myringotomy; cytological assessment of 30 and bacteriology of 28 effusions; histology and immunohistochemistry (CD3 for T-lymphocytes, Pax5 for B lymphocytes and MAC387 for macrophages) of 10 middle ear sections.

Results: Effusions were associated with neurological deficits in 6/16 (38%) and concurrent atopic dermatitis and otitis externa in 9/16 (56%) of live cases. Neutrophils and macrophages predominated on cytology (median 60 [range 2%-95.5%] and 27 [2%-96.5%]) whether culture of effusions was positive or not. In histology sections, the mucosa was thickened in affected dogs but submucosal gland dilatation occurred in affected and unaffected dogs. There was no bacterial growth from 22/28 (79%) of effusions. Bacteria isolated from the other 6 (21%) were predominantly Staphylococcus pseudintermedius (4/6, 67%).

Conclusions and clinical importance: Clinical, morphological, and cytological findings in middle ear effusions of dogs and people suggest similar pathogeneses. Middle ear effusion of dogs could be a useful model of human otitis media with effusion. Such comparisons can improve understanding and management across species.

Keywords: Cavalier King Charles spaniel; canine; immunohistochemistry; middle ear; otitis media with effusion.

FIGURE 1

A‐E, Cytology of canine middle ear effusions (MMEs) from cases of MEE. A, Thick mucus with enmeshed cells; B, thick mucus forming Curschmann's spirals (arrowheads). C, Vacuolated macrophages and neutrophils. D, Hemorrhage, erythrophagocytosis, leukophagocytosis, and intracytoplasmic hemosiderin (arrowhead) in a vacuolated macrophage. E, Degenerate neutrophils with intracellular bacteria (arrowhead), May‐Grünwald Giemsa stain. F‐O, Histological sections of canine tympanic bulla. F, Middle ear effusion fluid (arrowhead) containing mucus and many cells adjacent to the hypercellular inflamed mucosa (muc), hematoxylin and eosin (H&E). G, Macrophages predominate in the MEE fluid shown in (F), MAC387 immunohistochemistry. H, Dilatation and accumulation of secretion in the submucosal glands (arrowhead), H&E, and (I) mucus, Alcian blue. J‐L, Unaffected case with anatomically normal goblet cells adjacent to the eustachian tube (ET) ostium (arrowhead), H&E. K, Mucus accumulation at the ET ostium of the same case as (J), Alcian blue (arrowhead). L, Higher magnification image of goblet cells in the same case as (J) and (K), Alcian blue. M, Mucosa in unaffected dog has normal goblet cells (arrowhead), (N,O) thickened mucosa in different dogs with MEE; N, illustrates light infiltration of lymphocytes and plasma cells (arrowheads); and O, with congested (dilated) blood vessels (arrowhead). P, Morphometric analysis shows that the bulla mucosa is significantly thickened in bullae of dogs with MEE. Data in graph (P) are represented as points, the bar represents the median, and the error bars represent the interquartile range. Data were analyzed with a Mann‐Whitney U test. **P < .01 for 2‐tailed tests. et, eustachian tube; gc, goblet cell; n, neutrophil leukocyte; mee, middle ear effusion; muc, mucosa; vm, vacuolated macrophage. Scale bars = (A) 500 μm; (F,G,H,J,K) 200 μm; (B,C,I,M,N,O) 100 μm; (D,L) 50 μm; (E) 20 μm

FIGURE 2

Middle ear cytology. A, Mucus is significantly decreased and B, RBCs are significantly increased in culture‐positive middle ear fluids. The cellularity (C), WBC differential counts (D), and neutrophil karyolysis (E), karyorrhexis (F), and pyknosis grades (G) are not significantly different between culture‐positive and culture‐negative middle ear fluids. Note basophils and mast cells were not detected in the bulla fluid cytology preparations. Data in the graphs are represented as points. In graph (D) the bar, and in graphs (A‐C) and (E‐G), the histogram bar represent the median. The error bars represent the interquartile range. Data were analyzed with Mann‐WhitneyU tests. ns P > .05, **P < .01 for 2‐tailed tests were used. +, culture‐positive; −, culture‐negative; EOS, eosinophils; LYMP, lymphocytes; MØ, macrophages; NL, neutrophils