Introduction to Dermatology

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Introduction to Dermatology

• Clinical Pathology

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Function of the Skin

• Mechanical protection
• Environmental protection
• Water
• light
• Thermoregulation
• Sensory functions
• Pigmentation
• Prevents solar damage
• Metabolic/immunologic functions
• Secretion
• Excretion
• Vitamin D production
• Antimicrobrial action

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Structure of the Skin

• Epidermis
• Squamous keratinized epithelium (5 layers) sits
  on basement membrane
• Dermis
• Collagen fibers, blood, lymphatic vessels,
  nerves, fibroblasts, ground substance.
• Subcutaneous layer
• Hair follicles
• Epidermal invaginations into the dermis.

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Dermatologic Diagnostic Tools

• Signalment
• Breed, sex, age, color
• History
• Diet
• Environment
• Date of onset
• Acute vs. chronic
• Initial distribution of lesions
• Pruritic
• Physical Exam
• General PE
• Identify lesion
• Location of lesions/distribution
• Pruritis

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Diagnostic Tests

• Woods lamp
• Skin scraping
• Tape strip test
• Direct smear/impression smears
• Fungal cultures/ microscopic exams
• Bacterial culture
• Biopsy
• Fine needle aspirate
• Swab

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Skin Biopsy Punch
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Dermatologic Terms for Lesions

• Primary Lesion
• Develop spontaneously as a direct reaction of the
  underlying disease.
• Secondary Lesion
• Evolve from primary lesions.

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Primary Lesion Macule

• Circumscribed flat spot having color change.
• Petechia are hemorrhagic types of macules.

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Primary Lesion Papule

• Small, solid elevation of the skin
• Many are pink or reddish swellings
• Plaque
• A large flat top elevation formed by a coalition
  of papules.

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Primary Lesion Pustule

• Small, circumscribed elevation of the epidermis
  filled with pus.

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Primary Lesion Wheal

• A sharply circumscribed, raised, lesion
  consisting of edema.
• Hives

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Primary Lesion Vesicle

• Elevation of the epidermis with clear fluid
• Seen in viral or autoimmune dermatoses.

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Primary Lesion Tumor

• Neoplastic enlargement of subcutaneous tissues.

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Secondary Lesion Scales

• Accumulation of loose fragments of the keratin
  from the horny layer of the skin. (like dandruff)
• Epidermal collarettes
• A special type of scale arranged into a circular
  rim.
• Remnants of the roof of a vesicle or pustule.

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Secondary Lesion Crusts

• Form from dried exudate, serum, pus, cells, and
  scales.
• In pyodermas, crusts are yellowish-green.

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Secondary Lesion Excoriation

• Superficial removal of epidermis
• Usually self-induced due to pruritis
• Abrasion that is self-induced

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Secondary Lesion Ulcers

• A defect in the epidermis and exposing underlying
  dermis.

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Secondary Lesion Lichenification

• Thickening/ hardening of the skin
• Due to chronic friction or trauma
• Can see in elbow pads

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Secondary Lesion Hyperpigmentation

• Abnormal pigment of the skin

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Dermatophytosis/Ringworm

• Infection of the hair shafts and skin.
• Microsporum canis most common cause
• In rare instances- Microsporum gyseum and
  Trichophyton spp.
• Infective spores in soil, by direct contact, and
  by environmental fomites, ventilation.
• Trauma to skin may promote infection
• Other risk factors
• Age
• Immune competence
• Lesions may be circular, irregular, crusts,
  scales, hair thinning.

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Classification of Dermatophytes

• Anthropophilic
• Inhabit people only
• Zoophilic
• Inhabit both animals and people
• Geophilic
• Free-living saprophytes in soil. May be
  contaminant in cultures.
• Microsporum gypseum only species that causes
  lesions in animals.

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Diagnosis

• Woods Lamp
• 50 of Microsporum canis strains will fluoresce
  under a woods lamp.
• Looking for an apple green fluorescence
• Fungal Culture
• Saborauds medium or Dermatophyte Test Medium
  (DTM) specifically designed for ringworm
  diagnosis.
• Color change before 10 days
• Microscopic Exam of the colony

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DTM Procedure

• Pluck samples from suspicious lesions using a
  sterile hemostat.
• For asymptomatic carriers, use sterile toothbrush
  to comb cat fur.
• Place gently on DTM culture.
• Close lid of bottle, but do not tighten down.
• Store in darkened area.
• Results in 5-12 days.
• Positive result growth and color change at the
  same time (day).
• Check every other day after Day 3.

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Special DTM notes

• Pigs
• Often have contamination from geophilic/saprphytic
  fungi.
• Swab lesion with alcohol, let dry, then collect
  sample.

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Dermatophyte Identification using Colony
Morphology

• Microsporum canis Surface is white and woolly.
  Reverse side is yellow.
• Microsporum gypseum Surface is coarsely
  powdery, light tan to cinnamon brown. Reverse is
  brownish yellow.
• Trichophyton mentagrophytes Surface is cream
  colored and powdery. Reverse is yellowish to
  brown.

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Microsporum canis

• Confirm with microscopic exam
• Macroconidia have thick walls, spindle shaped
  8-15 cells and possess a terminal knob.

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Microsporum gypseum

• Spindle shaped but broader with no terminal
  knobs. Less than 6 cells on macroconidia.

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Trichophyton Mentagrophytes

• Few macroconidia, slender and cigar shaped with
  thin walls. Microconidia are numerous and
  arranged in grape-like clusters.

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Direct Microscopic examination of Ringworm

• Select a few hairs or skin scrape.
• May be suspended in mineral oil, through direct
  tape method or placed in a drop of 20 KOH (if
  use this method, gently heat and let stand for
  10-15 minutes).
• Examine under low and high power for fungal
  spores.
• If looking at colonies, tease out a little colony
  material and place on slide.
• Gently touch 2 cm strip of clear tape to surface
  of colony and then stain with new methylene blue
  or lactophenol cotton blue stains.

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Dermatophytosis treatment

• Systemic antifungals
• Griseofulvicin (expensive and hard to get)
• Clip hair/shave down
• Program (Lufeneron)
• Off label use
• Topical antifungals
• Miconazole, Chlorhexidine (malaseb shampoo and
  wipes), Ketoconazole (ketochlor shampoo), also
  topical lotions and creams.
• Solution of Lime-sulfur dip

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