Transcript Introduction to Dermatology

Clinical Pathology
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
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.
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
Diagnostic Tests
 Wood’s lamp
 Skin scraping
 Tape strip test
 Direct smear/impression smears
 Fungal cultures/ microscopic exams
 Bacterial culture
 Biopsy
 Fine needle aspirate
 Swab
Skin Biopsy Punch
Dermatologic Terms for Lesions
 Primary Lesion:
 Develop spontaneously as a direct reaction of the
underlying disease.
 Secondary Lesion:
 Evolve from primary lesions.
Primary Lesion:
Macule
 Circumscribed flat spot having
color change.
 Petechia are hemorrhagic types of
macules.
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.
Primary Lesion: Pustule
 Small, circumscribed elevation of the epidermis filled
with pus.
Primary Lesion: Wheal
 A sharply circumscribed, raised, lesion consisting of
edema.
 Hives
Primary Lesion: Vesicle
 Elevation of the epidermis with clear fluid
 Seen in viral or autoimmune dermatoses.
Primary Lesion: Tumor
 Neoplastic enlargement of subcutaneous tissues.
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.
Secondary Lesion: Crusts
 Form from dried exudate, serum, pus, cells, and
scales.
 In pyodermas, crusts are yellowish-green.
Secondary Lesion: Excoriation
 Superficial removal of epidermis
 Usually self-induced due to pruritis
 Abrasion that is self-induced
Secondary Lesion: Ulcers
 A defect in the epidermis and exposing underlying
dermis.
Secondary Lesion: Lichenification
 Thickening/ hardening of the skin
 Due to chronic friction or trauma
 Can see in elbow pads
Secondary Lesion:
Hyperpigmentation
 Abnormal pigment of the skin
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.
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.
Diagnosis:
 Woods Lamp:
 50% of Microsporum canis strains will fluoresce under a
woods lamp.
 Looking for an “apple green” fluorescence
 Fungal Culture:
 Saboraud’s medium or Dermatophyte Test Medium
(DTM) specifically designed for ringworm diagnosis.
 Color change before 10 days
 Microscopic Exam of the colony:
DTM Procedure
 Pluck samples from suspicious lesions using a sterile hemostat.
 For asymptomatic carriers, use sterile toothbrush to comb cat
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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.
Special DTM notes:
 Pigs
 Often have contamination from geophilic/saprphytic
fungi.
 Swab lesion with alcohol, let dry, then collect sample.
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.
Microsporum canis
 Confirm with microscopic exam
 Macroconidia have thick walls, spindle shaped 8-15
cells and possess a terminal knob.
Microsporum gypseum
 Spindle shaped but broader with no terminal knobs.
Less than 6 cells on macroconidia.
Trichophyton Mentagrophytes
 Few macroconidia, slender and cigar shaped with thin
walls. Microconidia are numerous and arranged in
grape-like clusters.
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.
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