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Steps for Diagnosing Dermatology Issues

September 6, 2016

When an animal is brought into a clinic with noticeable skin issues, many steps must be completed before a definitive diagnosis can be made. The following information describes the methods used to examine an animal in order to rule in or rule out various skin diseases that often present with similar symptoms.

Using Animal’s History to Diagnose Skin Disease

Obtaining the history of an animal is important to complete when working to diagnose a skin disease. The gathered information will help to identify between different diseases and will be used to:

  • Interpret the physical examination
  • Choose appropriate diagnostic tests

In order to provide all of the data that will help to form a diagnosis, the following general information should be gathered:

  • Past illnesses
  • Vaccination records
  • Husbandry, including:
    • Environment
    • Housing
    • Feeding practices
  • Any noticeable changes, for example:
    • Attitude
    • Consumption of food
    • Elimination routines
  • Recent exposure to other animals
  • Travel within the past 6 to 12 months

The next step to completing the history should include information that pertains to the animal’s dermatological issues. This detailed data should include:

  • Primary complaint
  • Information as to the onset of the disease, specifically the age when the issue began
  • Breed
  • Pruritus presence and severity
    • Include behaviors of animal such as:
      • Licking
      • Rubbing
      • Scratching
      • Chewing
  • Owner observations and description of:
    • The way the disease began and its progression
    • Types and development of lesions
    • Seasonality indications
    • Regional patterns, area on body where it was first noticed
    • Previous treatments and responses
    • Bathing frequency and time of last bath
    • Parasites observed
    • Contact with other animals
    • Housing changes
    • Indications of systemic illness or metabolic diseases

Physical Dermatologic Animal Examination

Since skin issues are often one of the first indications of a systemic illness, the animal should be given a thorough dermatological examination. Keep in mind that good lighting is essential when checking the animal’s hair coat and skin for:

  • Parasites
  • Clinical lesions
    • Distribution of lesions
      • Focal
      • Multi-focal
      • Diffuse
    • Region affected
    • Primary lesions and types, including:
      • Macules or patches
      • Papules or plaques
      • Pustules
      • Vesicles
      • Bullae
      • Wheals
      • Nodules or tumors
    • Secondary lesions and types, including:
      • Epidermal collarettes
      • Scars
      • Excoriation
      • Erosions or ulcers
      • Fissures
      • Lichenification
      • Calluses
    • Signs that lesions are either primary or secondary, such as:
      • Alopecia
      • Scale
      • Crusts
      • Follicular casts
      • Comedones
      • Changes in pigment

Animal Laboratory Diagnostic

Obtaining the laboratory diagnostic information necessary to determine a diagnosis for skin disease may include such steps as:

  • Skin scrapings
    • Superficial
      • Providing information from the epidermis surface
    • Deep
      • Provide information taken from within the hair follicle
  • Combing
    • Provides data through the collection of:
      • Skin debris
      • Trapped cutaneous parasites
  • Hair examination
  • Requires microscopic look at sampling of hair shafts that examines for:
    • Self-trauma
    • Dermatophyte infections
    • Dysplastic hair
    • Genetic diseases
  • Cytology
  • Cutaneous and auricular slides should be made, will be used to:
    • Identify bacterial, fungal, neoplastic skin diseases
  • Romanowsky-type stain is sufficient
  • Make at least:
    • 4 to 6 impressions smears
    • One slide by heat fixing before staining
  • In pruritic animals, obtain sampling scrape from beneath nail beds
  • Fungal cultures
  • Identify dermatophyte infections, work best by obtaining culture on either:
    • Dermatophyte test medium
    • Plain Sabouraud agar
  • On cats, comb a new toothbrush over the lesions
  • With dogs, obtain the sample by performing the toothbrush comb or by hair plucking
  • When hair plucking, wipe the hair with alcohol to prevent contamination
  • Bacterial cultures
  • Steps to culture include:
    • Do not scrub the site before sampling
    • Using a sterile needle, rupture the pustule and then swab with a sterile culture swab
    • With deep pyodermas, take swab from skin biopsy
    • Inform handlers of the type of suspected pathogens in order to obtain the proper type of culture procedure
    • Any systemic and topical agents should be withheld for at least 72 hours before obtaining sampling
  • Biopsy
    • Samples for skin biopsies should be taken when:
      • Skin disorders do not respond to therapy
      • Disorders appear severe or unusual
    • Samples should be collected from several different lesions
    • Examination should be completed by a pathologist trained in animal skin diseases
    • Test of choice – routine histopathology
  • Blood and Urine Tests
    • Obtaining information from routine blood and urine tests do not usually aid in the diagnosis of a dermatologic issue, but in cases where systemic illness is indicated, completing these tests may help to determine an underlying subclinical disease.

Diagnosing skin disease requires obtaining information gathered through a series of steps in order to determine a definitive cause.

To further discuss methods for diagnosing skin disorders, please contact your Covetrus  representative at 855.724.3461.

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