dermatology

• A full hair cycle lasts for around 4 to 6 weeks. Hair coats shed dependent upon the daylight hours and are hence melatonin and prolactin-driven

  • Short days lead to an increase in melatonin and a decrease in prolactin allowing for winter coat growth
• Skin is particularly rich in sweat glands but they are not present in the distal limb.

  • They are the most important cooling system
• Type 1 hypersensitivity: IgE mediated involving the release of histamine by mast cell, it is biphasic in nature and is aggravated after serial exposure.

  A) sweet itch

  
• Type 2 hypersensitivity: IgG-mediated cytotoxic response associated with complement binding.

  A) pemphigus

  
• Type 4 hypersensitivity: T-cell mediated.

  • Examples include insect-bites and drug eruptions
• Type 3 hypersensitivity: Immunocomplex deposition on endothelial beds. Neutrophil activation leads to vasculitis.

  A) purpura

  B) lupus

  
• With dermatology cases, a good clinical history is important and should include the following and more…

  • Horse signalment and if the horse has travelled abroad
  • Diet
  • Type of bedding
  • Lifestyle: out on pasture, stabled, type of barn…
  • Tack and general cleaning practices
  • Routine care and the last administration of endoparasites control, vaccinations, ectoparasites control
  • Other horses or people showing skin lesions
  • Details of skin condition
  • Location and duration
  • Localized or generalized
  • Presence of pruritus
  • Seasonality
  • Treatment attempts
• Lesion distribution can aid with the differential diagnoses…

  A) sweet itch

  B) pinworm

  C) lice

  D) fungal

  E) rain

  F) mud

  G) chorioptic mange

  H) lice

  I) contact

  
• fill in the blanks

  A) patch

  B) papule

  C) plaque

  D) vesicle

  E) pustule

  F) wheal

  G) nodule

  H) streoptococcal

  
• fill in the blanks

  A) alopecia

  B) scales

  C) crust

  D) erosion

  E) ulcer

  F) lichenification

  
• collection methods for diagnostics include…

  • Coat brushings
  • This is ideal for ectoparasites and the diagnostic aspect requires a magnification lens or microscope
  • Use seal containers if there is a delayed examination
  • Hair plucks
  • Skin scrapes
  • Biopsies
  • These can be excisional or punched and are ideal for nodules and deep pyodermas. They can then be sent off for culture and histology
  • Acetate tape: clear adhesive tape
  • Fine-needle aspirate
• describe the lice

  A) sucking

  B) biting

  C) feather

  
• To perform a hair pluck, grasp the hair firmly with haemostats and epilating on the hair direction. There should be a similar number of hairs in anagen and telogen

  • If there are fracture shafts then this indicates self-inflicted trauma e.g., pruritus
  • If there are swollen frayed shafts with fungal spores then this indicates dermatophytosis
  • If there are exclamation mark-shaped hair bulbs then this indicates alopecia areata
• Acetate tape strips can be used to diagnose oxyrus equi. To perform place tape on the anus, then apply it on a microscope slide
• what parasite is seen in the image?

  oxyrus equi

  
• To perform a skin scrape, use the back of 22 scalpel blade in the direction of the hair growth on the edge of the lesion until some ooze is obtained. This method is ideal for mites and dermatophytes (fungi)

  A) oil

  B) blue

  C) qPCR

  
• Fine-needle aspirates can be used for abscesses or masses and can be sent off for culture and cytology
• Diagnostic techniques of the samples include…

  • Cytology
  • This is an important diagnostic tool in skin disease and can be performed from scrapes, cytobrushes and impression smear (nodules).
  • Diff-quick most common and easy stain but you can also use Blue stain (methylene, blue/thiazine dye) for better visualisation of hyphae or a gram stain for bacteria
  • Cultures
  • Allergy tests - they are either unreliable or have poor repeatability
• Dermatophilus congolensis = rain scald
• Fungi should be cultured in what medium?

  Saboureau’s dextrose agar
• melanomas are most common in grey or white horses. It is rare for non-grey horses to get them but it can occur
• All grey horses have a gene mutation, STX17, which changes melanocyte behaviour leading to greying and more chance of vitiligo (pink muzzles) and melanomas
• All grey horses will develop melanomas over time and you can often see some small melanomas that the owner may not have noticed. The incidence increases with age and they usually develop between 4-8 years.
• There are four types of melanoma…

  1. Melanocytic nevi
  2. Dermal melanoma
  3. Dermal melanomatosis
  4. Malignant melanoma
• Melanomas form when there is a disturbance in melanin transfer from dermal melanocytes to follicular cells.
• Melanocytic nevi form single or multiple discrete nodules that are small and not obstructive
• The tail dock is the most common site for Dermal melanomas and they originate in the dermis (deeper than the melanocytic form)
• Dermal melanomatosis carries an increased risk of metastasis. The perineum is the common site for these confluent large melanomas
• Malignant melanomas are rare, invasive, and occur in (grey and non-grey) older horses. Recurrence is likely which makes treatment difficult. Mets form in various places but can infringe on the spinal cord or be found on the abdomen or diaphragm. In most cases, they have metastasised by the time of diagnosis.
• Melanomas can occur anywhere on the body (so should be a differential for a lump on any white/grey horse) but the most common locations are…

  • The tail (94%)
  • Perianal (43%)
  • Lips (33%)
  • Eyelids (24%)
  • Perineal
  • Back
  • Parotid
  • Lip commissures
• below is a melanoma

  A) differentiating

  B) pigmented

  C) pathologist

  D) bone

  
• Visual inspection and palpation play a large part in the diagnosis of melanomas. They are nodular skin masses but as they mature they can become necrotic in the centre (outstrip their blood supply) and then ooze a pigmented dark material.

  • They can become infected and get flystrike etc.
• For further diagnosis of melanomas, you can…

  • Perform an ultrasound
  • This can be helpful but won't help with specific identification of the mass
  • Ultrasound will just tell you that there is a mass
  • Biopsy
  • Once sent to a pathologist they will be able to identify the likely cause of the lump and if there is concern with neoplastic cells
  • FNA
  • Melanoma is the only mass that FNA is useful for in the equine species.
  • As they are full of melanin, you will see melanin pigment upon cytology
• You see this on FNA, what is your diagnosis?

  melanoma

  
• Sarcoids are benign (non-metastatic) however are locally aggressive and can be a cause for euthanasia so should be taken seriously. This occurs in all equids and hence can occur in donkeys, there is not a particular horse that is more commonly affected. They have a very high recurrence rate so can be hard to deal with.

  • Owners will trial some unusual treatment methods e.g. toothpaste and turmeric.

  The inner thigh is a common site for all (6) of the sarcoid types.
• what are the six sarcoid types?

  occult, verrucose, nodular, fibroblastic, mixed and malignant
• Occult sarcoids are the hardest to identify and you may not notice these unless the horse has been clipped or has a fine/hairless coat. They are relatively stable so are mild and superficial. They can remain unchanged for years so are often not problematic unless they are in an awkward position e.g. affecting tack.

  • However, they can also progress into other subtypes (e.g., mixed)

  They can occur peri-ocularly which makes them harder to treat. They have a small nodular component (cutaneous), and are quite roughened and flaky.

  • Hyperkeratotic in appearance.

  
• Verrucose sarcoids are rarely aggressive but can be annoying if occurring around the eyes. These are more warty in appearance (rough hyperkeratotic appearance with some flaking or scaling). Common to get them on the side of the sheath

  
• Nodular sarcoids vary in size (0.5-20cm) and form firm, spherical subcutaneous nodules. They can then be subcategorized into…

  • Type A: confined to subcutaneous tissues
  • These are easier to treat as you can shell them out and have a low recurrence rate when treated promptly.
  • Type B: some involvement of the overlying skin

  Palpation of a nodule is characteristic of the diagnosis

  
• Fibroblastic sarcoids are ulcerated, fleshy and aggressive-looking masses that grow aggressively so treat promptly. They can also be split into two groups...

  • 1: Pedunculated with a limited / small base that is palpable under the skin
  • These are cut off more easily as there is limited skin
  • 2: These have a wide base with often diffuse and ill-defined margins
  • These are very hard to treat.