Doramectin given at a dose rate of 0.6 mg/kg body weight by subcutaneous injection at weekly intervals is a useful and well-tolerated treatment for generalized demodicosis in the dog.

Background -There is a general belief that immune system cells are present in larger numbers in the planum nasale and adjacent haired skin than in other locations in the dog. However, little published information about the normal histological appearance of the skin of this area exists.Hypothesis/Objectives -The aim was to obtain information about the normal histological appearance of canine skin for specific anatomical regions of the planum nasale and the haired skin adjacent to the planum nasale.Animals -Samples from three sites were obtained from the planum nasale and adjacent haired skin of 25 dogs of varying age, breed and sex, with no evidence of dermatological or respiratory disease.Methods -Samples were analysed to determine and quantify the immune system cells present in the samples. Slides were stained with haematoxylin and eosin or toluidine blue; immunohistochemical stains for CD3 and CD79a were applied. Results -Immune system cells, including lymphocytes and plasma cells, were either very rare or present in low numbers. The majority of lymphocytes were of T-cell origin, with only infrequent B cells identified. Samples contained numerous melanophages, consistent with pigmentary incontinence, regardless of the presence or absence of inflammatory cells. Mast cells and plasma cells were present in low numbers.Conclusions -Inflammatory change noted in diagnostic biopsies from this area from dogs with clinical disease is likely to be of pathological significance. However, pigmentary incontinence appears to be common at this site in clinically normal dogs without significant inflammatory cell infiltration and is therefore not necessarily of pathological significance when seen in isolation in this location.

Pigmentary incontinence in the skin of the planum nasale from normal dogs We thank Danny Scott and William Miller for their letter regarding our finding 1 of pigmentary incontinence in the skin from the planum nasale and adjacent skin of dogs unaffected by dermatological or respiratory disease. In their letter they challenge this finding and, in particular, cite figure 4 of that article as demonstrating dermal melanocytes rather than melanophages.In our article we stated that "samples contained variable numbers of melanophages and, less commonly, free melanin granules within the superficial dermis, consistent with pigmentary incontinence, generally in the absence of observable inflammation". 1 We stand by this statement but accept that our figure 4 does not provide a good illustration of what we describe.It is often difficult to photograph free melanin pigment given the need to adjust fine focus during observation to appreciate the amount of this finely granular and often dispersed material. Close examination of figure 4 shows small clumps of melanin that do not appear to be associated with cells and are likely, therefore, to be free melanin. We do not dispute that many of the cells visible in figure 4 may represent dermal melanocytes rather than melanophages, and that this figure was not the optimal one to have been published; however, the cases regularly contained cells we believe to be melanophages. Furthermore, we believe that the differentiating features between melanophages and melanocytes cited by Scott and Miller in their letter may be overly simplistic.Given that we hypothesize that this pigmentary incontinence may be the result of chronic low grade trauma to the nasal planum (the nose frequently being a dog's primary interface with the environment), rather than the result of lichenoid inflammation, the melanophages seen in these clinically normal noses -which exhibited minimal or no inflammation at the time of biopsy -are likely to be quiescent, rather than actively phagocytic, and may therefore differ in appearance when compared to macrophages in actively inflamed lesions such as discoid lupus erythematosus. Interestingly, a survey of nasal biopsies from five clinically normal young dogs also found pigment incontinence in all cases, only two of which showed mild inflammation, which echoes our findings here. 2 It has been stated that it is difficult to distinguish melanocytes and melanophages by simple inspection of routine stained sections, 3 and that the morphology of the two cell types can overlap. 4 Immunohistochemistry is therefore likely to be required to fully elucidate the true ratio of melanophages to melanocytes in this instance. This is an area worthy of further attention. It continues to be our intention to carry out additional studies using the samples we have obtained in order to further characterize, amongst other features, the cells present, and this should include differentiating melanocytes from melanophages. We note that Scott and Miller have had to go back more than half a century to...

Four species of Demodex mite have to date been reported as affecting the brown rat. This paper describes the fi nding of a possible fi fth species. A pet rat was referred to a dermatology referral service in Queensland, Australia for evaluation of pruritus. Skin scrapings revealed the presence of numerous mites with the characteristic appearance of the genus Demodex, but with a truncated opisthosoma. Acaracidal treatment resulted in apparent clearance of the mites, but did not result in resolution of the pruritus.

No abstract