Morphology and Differential
Diagnosis
Welcome to Dermatology!
No matter what area of medicine or surgery
you pursue, you will get skin related
questions from family, friends, and
patients.
The time frame is short, so make the best
use of your time. Carry your book with
you at all times and try to make it through
all the photos.
Suggestions for a Successful
Rotation
• Be on Time!
• Be attentive and helpful.
• Do not ask questions or make comments
during the patient encounter. Please ask
all questions outside the exam room.
• Please do not talk loudly in the hallway.
Macule
Macule
Macule
Patch
Papule
Papules
Papules
Papules
Plaque
Plaque
Plaque
Nodule
Nodule
Nodule
Tumor
Tumor
Tumor
Pustule
Pustule
Vesicle
Vesicle
Vesicle
Bulla
Bulla
Wheals
Wheals
Special Skin Lesions
• Burrow: Thin linear papule or plaque
• Comedone: Follicular papule filled with
keratinous plug which is open or closed
• Cyst: Papule or nodule filled with debris
• Telangiectasia: Dilated blood vessel less
than 1 mm wide
Burrow
Comedone
Telangiectasia
Cyst
Secondary Lesions
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Scale
Crust
Erosions and ulcers
Excoriations
Fissures
Scars
Lichenification
Atrophy
Scales
Scales
Scales
Crust
Crust
Excoriations
Erosion
Erosion
Ulcer
Ulcer
Ulcer
Fissure
Fissure
Atrophy
Atrophy
Atrophy
Atrophy
Scar
Lichenification
Configuration
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Annular
Arcuate
Geographic
Discrete
Confluent
Serpiginous
• Linear
• Reticulated
Annular and arcuate
Linear
Erythema Subitum
Descriptors
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Punctate
Lichenoid
Umbilicated
Scarletiniform, morbiliform
Leonine
Color
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Pink
Violet
Orange
Blue
Green
Yellow
Black
Brown
Color
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Pink—Pityriasis rosea
Violet—Lichen planus
Orange—Juvenile xanthogranuloma
Blue—Amioderone skin pigmentation
Green—Pseudomonas
Yellow—Xanthomas
Black—eschar
Brown—Café au lait spots
Color
Distribution
Morphologic categories
• Macular-Patch
• Papular
• Papulosquamous
(scaly papules)
• Nodular
• Pustular
• Vesicular-bullous
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Urticarial
Petechial
Telangiectatis
Burrow
Poikiloderma
Hyperkeratotic/scale
Atrophic
“More is missed by not looking
than by not knowing”
M. McKay, M.D.
Procedures
• Liquid Nitrogen
• Electrodessication and curettage
• Biopsy
– Punch
– Shave
– Excision
Seborrheic Keratosis
• Common Skin Tumor of
unknown cause.
• Predilection for trunk,
scalp, temples
• No malignant potential
• Increase incidence with
age
• Easily treated with
curettage or
cryodestruction
Dermatosis Papulosa Nigra
• Most likely a subtype
of seborrheic
keratosis
• Malar areas, most
commonly on AfricanAmerican women
Acrocordons (Skin Tags)
• Common, occurring in
about 25% of adults
• More common in obese
individuals and often
develop in pregnancy
• Frictional areas such as
neck, axillae,
inframammary and groin
locations
• Can become irritated or
infarcted because of
torsion
Dermatofibroma
• Firm papule often with
brown pigmentation, most
frequently seen on the
anterior legs
• “Dimple” sign
• May be a reactive
process to an insect bite
reaction rather than a
tumor
• If multiple, sometimes
associated with systemic
lupus erythematosis
Dermatofibroma
Keloids
• Hypertrophic scar which
extends beyond the area of
injury
• May have delayed onset, even
up to years after injury
• Can be painful
• More common in AfricanAmericans
• Treatment can be difficult and
choices include intralesional
steroids, radiation, careful
excision, laser ablation
Epidermoid Cyst
Trichilemmal (Pilar) Cyst
Actinic Keratosis
Keratosis Pilaris
• Follicular papules, commonly on
extremities
• “sandpaper” feel
• 20% of the population affected
• Worsens in adolescence
• Common in Atopics and icthyosis
• May improve with keratolytics, retinoids,
dermabrasion
Keratosis Pilaris
Keratosis Pilaris
Cherry Angiomas
• Benign vascular proliferation
• “senile hemangioma” – don’t use this term
with patients 
• Usually appear on trunk, start at age 30,
increase with age
• Dilated capillaries
• Tx for cosmetic reasons only