Abstract
In order to improve the diagnostic value of histopathologic examination of skin biopsy samples from dogs with atopic dermatitis and, perhaps, to identify any differences from the normal state that may predispose to this skin condition, we compared the anatomic and cellular morphology of skin from three standard sites in 21 normal and 15 atopic dogs. The standard sites were lateral neck, dorsal rump, and craniolateral abdomen. No differences between the two groups were found in the means of area or thickness of the stratum corneum or the remainder of the epidermis at any site. The area of sebaceous glands, but not apocrine sweat glands, was larger in the atopic group (P ≤ 0.05 for the lateral neck skin and P < 0.1 for the dorsal rump skin). The mean number of non-metachromatic mononuclear cells in combined skin samples (126 μm2) in atopic dogs (91.0 ± 28.7) was significantly greater (P ≤ 0.01) than for the control normal dogs (65.3 ± 19.3); the mean number of mast cells in atopic dogs (12.39 ± 6.44) was similarly greater than in the controls (8.48 ± 5.14; P ≤ 0.1). Eosinophils were significantly increased in atopic dog skin (P ≤ 0.01), with the mean for all three sites combined of 0.81 ± 0.90 compared with a mean of 0.06 ± 0.15 for normal dogs. Numbers of circulating blood eosinophils were not significantly different in the atopic and normal group. Plasma histamine concentrations of 15.3 ± 7.8 for the atopics and 14.3 ± 4.1 for the normal dogs were not significantly different, although they were very high when compared to human values. Cutaneous histamine concentrations were always greater in the atopic dogs, although the difference was significant for only two of the three skin sites (P ≤ 0.05). Plasma histamine concentrations did not correlate with those of cutaneous histamine. There was a very good correlation between mast cell numbers and cutaneous histamine concentrations (r = 0.84). Total serum IgE levels were not significantly different in atopic and normal dogs, although the means, 182.6 ± 112.4 (normal) and 195.4 ± 108.8 (atopic), are high when compared to serum concentrations in human beings. There was no correlation between serum IgE concentrations and those of plasma histamine. By confirming that numbers of cutaneous mast cells, non-metachromatic mononuclear cells, and eosinophils are significantly increased in the skin of atopic dogs in comparison to that of normal dogs, these data increase the validity of using such criteria for diagnostic purposes.