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dermatology
7003/morris

holm: introduction/anatomy of the 
skin
gomez: descriptive dermatology/diagnostic methods

interesting skin 
facts:
-largest organ
-puppies: skin/subcu - 24% body weight, 12% in 
adults
- k9 skin thickest over neck, back, thinnest in axilla, groin, 
pinna

k9 skin has thinner epidermis than human skin
k9 skin pH is higher 
than human skin - important when considering shampoo. human products may 
irritate dog skin

dogs have cyclic hair growth; humans continuous

epidermal turnover is quicker - about 20 days in dogs.

functions: 
thermoregulation - keeping you warm. protection - keeps bugs out. 
sensory, fat storage, protection from radiation...

layers of epidermis:

-stratum basale: deepest layer
-stratum spinosum
-stratum granulosum

-stratum corneum

main function is to produce stratum corneum, which is 
the main protective layer.
recall as you move outward you lose the nuclei 
and gain some granules.

slide: spiny layer
slide: granular layer (dark 
granules present)
slide: cornified layer (no nuclei present)

cells of 
epidermis:

1. keratinocyte
2. melanocyte - contains melanosomes
3. 
langerhans cells - APC of skin - picks up Ag, goes to LN, shows to T 
cell.
4. merkel cells - vacuolated, clear cell - involved in sensory 
perception

Dermis: 
-basic framework of skin
-provides elasticity and 
support
-separated from epidermis by BM
-collagen, elastin, appendageal 
structures, blood vessels, nerves, dermal cells. 

important dermal cells

-fibroblasts: make collagen
-mast cells: involved in immune function, 
allergy
-histiocytes: function partly unclear, immunosurveillance

slide: 
mast cell with granules

epidermal appendages:

1. hair follicles
2. 
arrector pili muscles: more numerous along the back, make hair stand up

3. sebaceous glands: empty into hair follicle. produce sebum for 
waterproofing. sebum functions: waterproofinng, luster/sheen of haircoat, 
heat transfer, bacteriostatic/fungistatic, marking/sexual attraction. the 
largest sebaceous glannds are at eyellids, lips, chin, dorsum, sterum, 
vulva, scrotum, anus. hormonal control of sebum: increase: androgens, 
progesterone, thyroid hormone; decrease: estrogen, corticosteroids
4. 
apocrine sweat glands: in deep dermis, secrete milky protein/lipid fluid

5. eccrine sweat glands - only on footpads in dog/cat - possible marking 
function, little or no thermoregulation
6. primary and secondary hairs


slide: sebaceous gland
slide: SEM of hair, cornified epithelium
slide: 
sebaceous gland
slide: apocrine sweat gland

Panniculus/hypodermis: subcu 
fat - insulation, storage of calories, structural support.

Hair: stages 
of growth: anagen, catagen, telogen (ACT)
anagen: growing stage
catagen: 
short transitional stage
telogen: resting stage

there is a cortex and 
medulla to hair shaft; cuticle is protective coating.
in telogen there is 
no outer root sheath

hir cycle is controlled by photoperiod, 
temperature, all sorts of things. 
telogen defluxion/effluvium: occurs 
with severe stress, dogs/cats/people who are really sick, all hair goes 
into telogen at the same time, and then when anagen starts, all the 
telogen hairs shed out at the same time causing partial or total 
alopecia. 

in dog/cat - hair replacement is mosaic - in different areas, 
not all one area at the same time.

hormonal influences - things that 
increase sebum production will increase hair growth, and things that 
decrease it decrease hair growth.

tylotrich pads : mechanoreceptors - 
slow adapting
inverse relationship b/w density of haircoat and thickness 
of epidermis
dogs/cats - compound hair follicles - many secondary hairs 
with each primary hair, meaning dense haircoat.
cat has thicker, denser 
haircoat than dogs, though each hair is thinner.

Primary skin lesions:

-early lesions which develop from normal skin
-most diagnostic type of 
lesion

macule/patch:
-circumscribed area, flush with skin surface, not 
raised or indurated, characterized by change from normal skin color

-macules >1cm diameter are called patches
-erythematous, hyperpigmented, 
or hypopigmented.

papule:
-small, solid elevation of skin, often red or 
pink
-follicular - bacteria, dermatophyte, demodex
-non-follicular - 
ectoparasites
-usually progress into pustules

in a skin infection, 
papules become pustules which rupture, form crusts, and then leave behind 
a scale.

Nodule:
-circumscribed solid elevation
-extends into deeper 
layers of skin (dermis, panniculus)
-inflammatory or neoplastic in origin


Tumor:
-swellling or enlargement that involves any skin strutcure

-usually neoplastic
-benign or malignant
slide: skin tumors - 
papillomas/skin tags.
slide: melanoma

Pustule:
-small, circumscribed 
elevation of skin , filled with pus
-follicular or nonfollicular 

-follicular: caused by bacteria (pyoderma) is most common, also 
dermatophytes or demodex
-nonfollicular: less common, due to immune 
mediated disease - pemphigus foliaceous, subcorneal pustular dermatitis

-always lance and make smears of these.

Wheal:
-a sharply circumscribed 
raised lesion caused by dermal edema - like a hive
-many wheals = 
urticaria (often allergic reaction)
-hairs on the wheal do not epilate 
easily

vesicle:
-small, sharply circumscribed elevation of skin filled 
with fluid (blister)
-less than or equal to 1 cm in diameter (if larger, 
it's a bulla)
-clear, proteinaceous, relatively acellular fluid

-characteristic of  pemphigus group of autoimmune dz - form when 
desmosomes b/w spiny cells break down

bulla: 
-large vesicle

plaque:

solid skin elevation made of one cell type, over 1 cm in diameter
usually 
alopecic and erythematous
made of eosinophils (cats), lymphocytes 
(cutaneous lymphoma) etc

Secondary skin lesions:
-secondary to some 
other pathologic skin change
-usually nondiagnostic on biopsy

Scale:

-normal accumulation of exfoliated fragments of cornified cel layer - aka 
dandruff
-excessive scale indicates rapid skin turnover (seborrhea), dry 
skin (xerosis), low sebum production (sebaceous adenitis), or any 
pruritic dermatosis.
-epidermal collarette -  circular or semicircular 
accumulatoin of scale following rupture of a pustule, vesicle or bulla - 
usually there is an area of hyperpigmentation in the middle. usually 
hallmark of pyoderma

crust:
-dried exudate of the surface of a lesion - 
from pustule, or erosions
-serous: yellow/honey colored - contains serum 
+/- WBC. these involve only the epidermis, and usually there are erosions 
under the crust - NOT ulcers
-hemorrhagic: brown/red - serum, WBC, RBC. 
involve epidermis and dermis - breach of BM has occured. there are ulcers 
below these crusts.

erosion:
superficial defect of skin, partial or 
complete loss of epidermis
form serous crusts, heal w/o scarring

ulcer:

deep defect of skin due to complete loss of epidermis and partial to 
complete loss of dermis.
BM zone breached
hemorrhagic crusts occur
heal 
with scarring
"indolent ulcer" in cats - slide.

excoriation:
-erosions, 
ulcers, due to self induced physical trauma - scratching, biting

-indicates pruritis

hypopigmentation:
-can be normal for some animals

-associated with vitiligo, autoimmune dz, uveodermatologic syndromes, 
discoid lupus, color dilution abnormalities
-leukoderma: loss of skin 
pigment
-leukotrichia: loss of hair pigment
-can be post-inflammatory - 
black people and animals can have loss of pigmentation after an 
inflammatory response such as vaccine induced, or injury. hair that grows 
over brands is usuallyl white

hyperpigmentation:
-excessive coloration 
of skin
-usually postinflammatory and takes 30 days to develop
-takes 1-6 
mos to resolve once underlying cause is removed

lichenification:

-thickening and hardening of the skin, characterized by exaggeration of 
superficial skin markings, cobblestone appearance
-usually sseen with 
hyperpigmentation
-due to chronic pruritis, trauma

scar: 
hard plaque of 
dense, fibrous tissue that has replaced damaged dermis; often covered by 
atrophic epidermis- saran wrap appearance. very soft feeling.


hyperkeratosis: 
increased thickness of horny layer
-gross lesions seen 
on planum nasale, footpads
-can be orthokeratotic (no nuclei) or 
parakeratotic (increased turnover, nuclei present)


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fissure: a splitting or discontinuity of a surface
-linear defect that 
extends through epidermis into the dermis
-planum nasale, footpads often 
affected

comedo (comedones)
-blackheads
-plug of keratin and dried sebum 
in a hair follicle
-dark brown or black
-most commonly on ventral abdomen

-variable size
-usually associated with cushings, seborrhea, schnauzer 
comedo syndrome, acne

hyperhydrosis:
-excessive sweating
-really not a 
problem in dogs/cats
-associated with atopy (pollen allergy)
-occurs on 
ventral abdomen

alopecia:
-loss of hair
-complete alopecia: skin with 
entire hair missing (focal or diffuse)
-stubble alopecia: hair loss where 
only the distal part of the hair is lost (focal or diffuse), usually due 
to pruritis

slide: dog with hair missing around eye, but there is some 
stubble. this hair was lost due to dog rubbing face on furniture and 
breaking hair off - stubble alopecia.  

causes of focal, complete 
alopecia:
-folliculitis (bacterial, dermatophyte, demodex) - remember 
this
-dermal/epidermal nodule/tumor
-scarring
-alopecia areata (a disease 
- autoimmune against hair follicle)
-iatrogenic (injection, radiation)

-congenital (hypotrichosis)

slide: complete alopecia - zinc responsive 
dermatopathy. you don't have to remember all these diseases, by the way. 
this dog has hair loss on muzzle, around eyes.

slide: bald cat - stubble 
alopecia.

stubble alopecia:
-flea allergy dermatitis
-food allergy

-atopy
-scabies, cheyletiella, pediculosis
-psychogenic: dx by exclusion

-dermatophytosis

causes of generalized complete alopecia:

endocrinopathies: cushings, hypothyroidism, adult-onset GH deficiency, 
sex hormone imbalance
color mutant alopecia/black hair follicular 
dysplasia
telogen effuvium
physiologic
congenital
ectodermal dysplasia - 
lack of follicles

remember: complete alopecia can be generalized or 
focal - complete simply means the whole hair is gone. stubble alopecia - 
bulb of hair is still in follicle.

Erythema:
-redness of the skin

-produced by congestion and dilation of the dermal vasculature

-inflammation, wounds, pruritis...
slide: white dog who looks pink

Quick 
and easy dermatological dx tests:

there is a lot of skin out there and a 
lot of it has problems, you will see derm problems daily, so these tests 
will be helpful for you.

skin scraping: 
always do one on a dog with a 
skin problem - always
multiple deep scrapings should be done on any areas 
of alopecia
squeeze skin, scrape with ddull blade coated in mineral oil 
until capillary bleeding is see
dx: demodex, sarcoptes, cheyletiella, 
otodectes, lice. 

KOH/CPL preps:
-rarely done
-great test, handy, if you 
have a spare half hour
these solutions clear debris whenn examining hairs 
or scrapings for dermatophyte spores
stir collected material into 2-3 
drops of KOH, use coverslip, look for spores

epilation and microscopic 
exam of hair:
if a cat comes in and you're not sure what's going on  - 
pluck hair, put it on slide in some oil - look at ends. do they taper off 
to a point, or are they blunt?  if blunt - scratching, biting, chewing, 
etc. one caveat - if animal is groomed, clipped, etc - will be blunt 
ended hairs. 

flea combing - this is the second imperative test. do this 
first, then skin scrape. flea combs have 32 tines per inch. can catch 
fleas or cheyletiella mites. will collect flea dirt, scale. put debris on 
moist paper towel, look for rust colored stains to indicate flea dirt.

slide: dog whose whole back half is bald. this is just from flea allergy.


pinnal-pedal reflex: ear scratch reflex test.
look at ear margin for 
scaling, crusting, seborrhea
rub or scratch peripheral 1 cm of ear margin

positive response: rear leg reflexively scratches
false positive: ear 
canal or central pinnal disease present
85-90% diagnostic for scabies - 
these dogs are exquisitely itchy. can treat even if you don't find mites 
b/c hard to find them on scraping slides

impression smears:
used on 
pustules, vesicles, or bullae
use 25 ga needle to gently lift open the 
lesion, press a glass slide against the fluid 10-20 times, gently 
allow 
it to dry, stain with diff-quik
put on a drop of mineral oil and  
coverslip and look under 40x
look for cocci, PMNs, cell

pyoderma: 
degenerate neutrophils, numerous cocci, rare acantholytic cells.

pemphigus foliaceous: intact, mature PMNs, rare cocci, frequent 
acantholytic cells.

diascopy - skipping this, not done often
fecal - 
skipping

acetate tape preparations: scotch tape preps
helpful with 
cheyletiella, lice - put tape on skin to collect scale and stuff, then 
place sticky side down on glass slide and look microscopically for mites, 
lice - look at 10x with low light.

Intradermal skin tests for atopy: 
IDST is the gold standard test for atopy. you put antigens into skin in a 
shaved area and look for wheal formation. this is the standard method for 
dx of allergic atopy in dogs. 
more accurate than serology/elisa


serologic allergy tests:
elisa/rast: looks for circulating IgE - high 
degree of false positives, poor reproducibility. advantages - no shaving, 
no sedation, can do test even if skin is inflamed.

fungal cultures: the 
most important things you do in your office initially are flea combing, 
skin scraping, and then fungal culture. pluck hairs from lesions and put 
into dermatophyte medium. look for it to turn red in presence of 
microsporum canis. also, fluffy white colonies grow. then take some of 
the white stuff and look at it microscopically. takes 10-14 days to grow.


wood's light:
UV light filtered through a cobalt or nickel filter
hairs 
infected with m.canis have apple-green fluorescence 50% of the time
false 
positive: keratin, soap, petroleum, other meds
false negatives: 
non-fluorescent dermatophytes, iodine
fluorescing hairs should be plucked 
with forceps to examine microscopically or to inoculate fungal medium.


bacterial c&s - lance pustule with 25 ga needle and use sterile 
culturette to take sample. 

skin biopsy: for histopathologic diagnosis. 
this will be on the test. section F page 7 of handout - when and what to 
biopsy. that will be a test question. this is very important. ***

when 
and what to biopsy:***
1. all obviously neoplastic, or suspected 
neoplastic lesions: looks like tumor
2. all persistent ulcerations, 
vesicular diseases
3. deep infections with draining tracts (nocardia, 
mycobacteria...)
4. unusual, bizarre, or severe lesions
5. disease not 
responding to rational treatment
6. when disease you suspect is expensive 
to tx, or tx may have side effects.
7. when the dz you suspect is best 
dxd by bx

always biopsy more than one lesion! if there are 6 affected 
areas, take part of all 6. and always send sample to a real 
dermatopathologist, not a regular pathologist.

slide: dog with severe, 
bizarre, and unusual lesions

golden retriever came to local vet with 
large flaky dandruff. vet started allergy tx, which was appropriate. used 
hydroxyzine rx and medicated baths. dog kept getting worse, then started 
getting these ulcers. started abx tx - no improvement. started losing all 
of his hair. after 8 mos, came here to ES. this was cutaneous LSA. this 
dog should have had a biopsy when he failed to respond to the original 
therapy! the owners spent like $2000 trying to make him better, too, when 
he had a basically terminal disease.

to do a skin biopsy - some dogs 
require sedation, some do not. use local anesthesia - 0.5 cc 
lidocaine/epi infiltrate area (if near eye, nose, footpad always 
sedate/anesth). if you sedate dog,use 4 mm punch as opposed to larger, 
b/c will bleed a lot. use small punch for nose, feet, too. stick punch 
in, then grasp subq fat and remove specimen w/o daamaging the dermis. put 
into 10% formalin. no surgical prep required unnless sending for 
culture/sensitivity.

remember ** always flea comb, skin scrape, fungal 
culture **
know skin biopsy technique, a bit about fungal cultures
pay 
attention...
question will be about why/when to biopsy, not how to biopsy

know about differences b/w tests for atopy - diff b/w elisa and IDST
know 
about types of alopecia and causes of alopecia


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