Laboratory evaluation of skin and ear disease

image of Laboratory evaluation of skin and ear disease
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Very few skin disorders have an unequivocally pathognomonic appearance and almost all require some form of laboratory investigation to confirm the diagnosis. Fortunately, the skin is readily accessible. Most tests are straightforward and can be accessed in a practice laboratory. This chapter considers the investigation of skin disease and otoscopes and examination of the ears. Case examples are also considered.

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26.2 (a) Adhesive tape strip preparation from a dog with dermatitis stained with the ‘one-stain’ method. (Rapi-Diff II stain; original magnification X400). (b) Adhesive tape strip preparation from the same dog as (a) stained with the ‘two-stain’ method. (Rapi-Diff II stain; original magnification X400)
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26.4 Anagen hairs from a German Shepherd Dog. (Original magnification X40)
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26.5 Telogen hairs from a crossbred dog with hyperadrenocorticism. (Original magnification X40)
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26.6 Follicular casts from a dog with sebaceous adenitis. (Courtesy of Dr Bob Kennis)
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26.7 Ectothrix spores on a damaged hair from a cat with a infection.
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26.8 on dermatophyte test medium. Note that the red colour change coincides with early fungal growth.
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26.9 macroconidia from culture; these are not produced . (New methylene blue stain; original magnification X400) (Courtesy of Professor Susan Dawson)
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26.11 Ectoparasite identification key for (a) insects and (b) mites and ticks. This figure was produced with the assistance of Merial Animal Health.
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26.12 Flea faecal pellet. (Original magnification X100) (Courtesy of Peter Forsythe)
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26.13 Tape strip cytology. (a) Tape-stripping from the skin. (b) Forming a loop on a microscope slide. (c) Staining in a Diff-Quik stain.
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26.14 Impression smear from a pustule. (a) Rupture the pustule with a sterile needle. (b) Absorb the contents on to a swab. (c) Gently make a thin impression by rolling the swab on a microscope slide. Too much smearing will rupture the cells.
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26.15 Algorithm for interpreting cutaneous cytology preparations.
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26.16 Inflammation. (a) Acute inflammation in a sample from a dog with otitis externa; note the preponderance of degenerate neutrophils. The insert shows a close-up of degenerate neutrophils containing phagocytosed rod-shaped bacteria. (Diff-Quik stain; original magnification X400; inset X1000). (b) Chronic inflammation in a dog with deep pyoderma; there is a mixture of neutrophils and macrophages. (Diff-Quik stain; original magnification X400)
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26.17 Neutrophils. (a) Degenerate cells in a staphylococcal pyoderma; note the swollen, fragmented nuclei (karyorrhexis), nuclear rupture and streaming, and swollen cytoplasm. There are numerous bacteria seen associated with neutrophils and extracellularly. (Diff-Quik stain; original magnification X1000). (b) Non-degenerate neutrophils admixed with squamous epithelial cells; note the shrunken, hypersegmented intact nuclei. (Diff-Quik stain; original magnification X1000) (b, © Tim Nuttall)
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26.18 Acanthocytes and neutrophils in a smear from a pustule in a dog with pemphigus foliaceus. (Diff-Quik stain; original magnification X400)
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26.19 Performing a punch biopsy. (a) Draw a circle around the biopsy site and then bisect the circle with a line in the direction of hair growth. (b) Infiltrate the skin with local anaesthetic, introducing the needle outside the circle to avoid trauma to the biopsy site. (c) Press a 6 mm biopsy punch against the skin and rotate in one direction. (d) Dissect free from the underlying tissues, taking care not to damage the biopsy specimen. (e) Blot any excess blood away using a swab and fix in a 10X volume of 10% neutral buffered formalin. Note the line indicating the direction of hair growth.
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26.20 Multiple positive reactions to house dust mites and pollens in an atopic Shar Pei. Positive reactions are identified by erythema and swelling.
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26.21 (a) Schematic representation of a typical ELISA test for allergen-specific serum IgE. The sensitivity and specificity of the test depends on the efficiency with which the IgE detection reagent detects the allergen-bound IgE. (b) Monoclonal anti-IgE antibodies specific for certain IgE epitopes are highly specific (i.e. there are few false positives) but may be less sensitive if they fail to detect allergen-specific IgE without that particular epitope (i.e. there may be more false negatives). Polyclonal antibodies or oligoclonal antibody mixes recognize a greater range of epitopes and may therefore be more sensitive. However, if some epitopes are shared with IgG these tests may be less specific, with more false positive results.
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26.22 Contact reaction to an adhesive bandage in a dog.
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26.23 A normal tympanic membrane seen through a video otoscope. Note the taut and translucent pars tensa (pt), the dorsal, fleshy pars faccida (pf) and the C-shaped manubrium (m) of the malleus. (© Karl Storz Endoscopy UK Ltd, Dundee, UK)
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26.24 Oval and budding yeasts overlying pale-staining, angular keratinocytes. (Diff-Quik stain; original magnification X400)
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26.26 (a) Numerous extracellular and intracellular staphylococci, (b) and degenerate neutrophils. Note the nuclear streaming from ruptured nuclei. (Diff-Quik stain; original magnification (a) X400, (b) X1000)
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26.27 3-year-old crossbred dog exhibiting pruritus and alopecia.
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26.28 Close-up of the affected skin on the ventrolateral abdomen.
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26.29 Palmar aspect of an affected forefoot.
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26.30 Adhesive tape cytology from the ventral abdomen. (Modified Wright–Giemsa stain; original magnification X400)
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26.31 Indirect impression smear cytology from an affected foot. (Modified Wright–Giemsa stain; original magnification X400)
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26.32 Stained needle core cytology smear from a popliteal lymph node. (Modified Wright–Giemsa stain; original magnification X400)
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26.33 Hair pluck from ventral neck. (Original magnification X100)
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26.34 9-year old Bichon Frise exhibiting alopecia.
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26.35 Close-up of the flank skin.
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26.36 Close-up of lesional skin from the flank.
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