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DERMATOLOGY
Dr. N. Shear
Blaise Clarkson and Elana Lavine, chapter editors
Harriette Van Spall, associate editor
Primary Morphological Lesions
Secondary Morphological Lesions
Other Morphological Lesions
USEFUL DIFFERENTIAL DIAGNOSES . . . . . . . 3
Differential Diagnosis by Morphology
Differential Diagnosis by Location
COMMON SKIN LESIONS . . . . . . . . . . . . . . . . . . 5
Hyperkeratotic
Fibrous
Cysts
Vascular
Melanocytic Nevi
Miscellaneous
ACNEIFORM ERUPTIONS . . . . . . . . . . . . . . . . . . 11
Acne Vulgaris/Common Acne
Rosacea
Perioral Dermatitis
DERMATITIS (ECZEMA) . . . . . . . . . . . . . . . . . . . 13
Contact Dermatitis
Atopic Dermatitis
Seborrheic Dermatitis
Stasis Dermatitis
Nummular Dermatitis
Dyshydrotic Dermatitis
Diaper Dermatitis
INFECTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Bacterial
Superficial Skin (Epidermal)
Deeper Skin (Dermal)
Hair Follicles
Periungual Region
Sexually Transmitted Infections
Viral Infections
Dermatophytosis
Yeast
Parasitic
PAPULOSQUAMOUS DISEASES . . . . . . . . . . . . 25
Psoriasis
Psoriasis Arthritis
Lichen Planus
Pityriasis Rosea
VESICULOBULLOUS DISEASES . . . . . . . . . . . . . 28
Pemphigus Vulgaris
Bullous Pemphigoid
Dermatitis Herpetiformis (DH)
Porphyria Cutanea Tarda
Differential of Primary Bullous Disorder
MCCQE 2006 Review Notes
DRUG ERUPTIONS . . . . . . . . . . . . . . . . . . . . . . . . 30
Exanthematous Eruptions
Urticaria
Fixed Drug Eruption
Delayed Hypersensitivity Syndrome
Photosensitivity Eruptions
Serum Sickness - Like Reaction
ERYTHEMA MULTIFORME (EM), . . . . . . . . . . . 32
STEVENS-JOHNSON SYNDROME (SJS) AND
TOXIC EPIDERMAL NECROLYSIS (TEN)
ERYTHEMA NODOSUM . . . . . . . . . . . . . . . . . . . . 33
MALIGNANT SKIN TUMOURS . . . . . . . . . . . . . . 33
Basal Cell Carcinoma (BCC)
Squamous Cell Carcinoma (SCC)
Malignant Melanoma
Others
HERITABLE DISORDERS . . . . . . . . . . . . . . . . . . 36
Ichthyosis Vulgaris
Neurofibromatosis (NF)
Vitiligo
SKIN MANIFESTATIONS OF INTERNAL . . . . . 37
CONDITIONS
Autoimmune Disorders
Endocrine Disorders
HIV
Malignancy
Others
Pruritus
WOUNDS AND ULCERS . . . . . . . . . . . . . . . . . . . 39
ALOPECIA (HAIR LOSS) . . . . . . . . . . . . . . . . . . . 39
Non-Scarring (Non-Cicatricial) Alopecia
Scarring (Cicatricial) Alopecia
NAILS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
TOPICAL THERAPY . . . . . . . . . . . . . . . . . . . . . . . . 41
Vehicles
Topical Steroids
Dry Skin Therapy
COSMETIC DERMATOLOGY . . . . . . . . . . . . . . . 43
Chemical Peel
Laser Therapy
SUNSCREENS AND PREVENTIVE . . . . . . . . . . . 43
THERAPY
REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Dermatology – D1
2
APPROACH TO THE DERMATOLOGY . . . . . . . 2
PATIENT
History
Physical Exam
DEFINITIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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APPROACH TO THE DERMATOLOGY PATIENT
HISTORY
age, race, occupation (especially exposures), hobbies
details of skin eruption should include:
• location, onset, duration (persistent versus intermittent eruption)
• alleviating and aggravating factors (plant contact, cosmetic/jewellery use,
exposure to heat/cold/sunlight, relationship to foods/spices)
• associated skin symptoms
• changes in sensation (itchiness, burning, pain)
• changes in surface (dryness versus discharge)
• past history including investigations and therapy
associated systemic symptoms (weight loss, malaise, fever, diarrhea, arthralgias, muscle weakness)
medications and allergies
past dermatological history
family history of atopy, skin cancer, psoriasis
PHYSICAL EXAM (How to describe a Lesion)
S ize
C olour (e.g. hyperpigmented, hypopigmented, erythematous)
A rrangement (e.g. solitary, linear, reticulated, grouped, herpetiform)
L esion morphology (see Table 2)
D istribution (e.g. dermatomal, intertriginous, symmetrical/asymmetrical, follicular)
Always check hair, nails, mucous membranes and intertriginous areas
Table 1. Skin Phototypes
Phototypes
Colour of Skin Without
Skin’s Response to Sun Exposure
Sun Exposure
I
White
Always burns, never tans
II
White
Always burns, little tan
III
White
Slight burn, slow tan
IV
Pale Brown
Slight burn, faster tan
V
Brown
Rarely burns, dark tan
VI
Dark brown/black
Never burns, dark tan
DEFINITIONS
PRIMARY MORPHOLOGICAL LESIONS
Table 2. Types of Lesions
< 1 cm Diameter
1 cm Diameter
Raised Superficial Lesion
Papule (e.g. wart)
Plaque (e.g. psoriasis)
Palpable Deep (dermal)
Nodule (e.g. dermatofibroma)
Tumour (e.g. lipoma)
Lesion (not necessarily raised)
Flat Lesion
Macule (e.g. freckle)
Patch (e.g. vitiligo)
Elevated Fluid-filled Lesions Vesicle (e.g. herpes simplex virus (HSV)) Bulla (e.g. bullous pemphigoid)
primary lesion : an initial lesion that has not been altered by trauma or manipulation, and has
not regressed
pustule : a vesicle containing purulent exudate (white, yellow, green)
cyst : a nodule containing semisolid or fluid material
erosion : a disruption of the skin involving the epidermis alone
ulcer : a disruption of the skin that extends into the dermis or deeper
wheal : a special form of papule or plaque that is blanchable and
transient, formed by edema in the dermis (e.g. urticaria)
scar : replacement fibrosis of dermis and subcutaneous tissue
SECONDARY MORPHOLOGICAL LESIONS
develop during the evolutionary process of skin disease, or are created by manipulation
or complication of primary lesion lesion (e.g. rubbing, scratching, infection)
crust : dried serum, blood, or purulent exudate originating from a lesion (e.g. impetigo)
scale : excess keratin (e.g. seborrheic dermatitis)
D2 – Dermatology
MCCQE 2006 Review Notes
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DEFINITIONS . . . CONT.
fissure : a linear slit-like cleavage of the skin
excoriation : a scratch mark
lichenification : thickening of the skin and accentuation of normal
skin markings (e.g. chronic atopic dermatitis)
xerosis : dryness of skin, eyes and mouth
atrophy : histological decrease in size and number of cells or tissues
resulting in thinning or depression of the skin
OTHER MORPHOLOGICAL LESIONS
comedones : collection of sebum and keratin
• open comedone (blackhead)
• closed comedone (whitehead)
purpura : extravasation of blood into dermis resulting in
hemorrhagic lesions
• petechiae : small pinpoint purpura
• ecchymoses : large flat purpura
telangiectasia : dilated superficial blood vessels; blanchable
USEFUL DIFFERENTIAL DIAGNOSES
Table 3. Differential Diagnosis by Morphology
Dermatitis
Nondermatitis
(epidermal cells produced
Atopic Dermatitis (flexural folds)
Psoriasis (elbows/knees/scalp,
from excessive and
Nummular Eczema (coin-like, isolated)
Discoid Lupus (don’t see hair follicles)
abnormal keratinization
Seborrheic Dermatitis (scalp/nasolabial folds/chest)
Drug reaction (e.g. gold)
and shedding)
Lichen Planus (flat surface, lacy lines
on surface)
Mycosis Fungoides (girdle area, leonine facies)
Pityriasis Rosea (Christmas-tree distribution)
Secondary Syphilis (palms + soles,
copper coloured)
Tinea (well demarcated, raised border)
Inflammatory
Proliferative
Discrete Red Papules
Acne (teenager, face/chest/back)
Dermatofibroma (“dimple sign”)
(elevated/solid lesion < 1 cm)
Bites/Stings (history of outdoors, central punctum)
Hemangioma (blanching)
Folliculitis (in hair follicle)
Psoriasis
Furuncle (very painful, central plug)
Hives (whitish border, pruritic)
Inflamed Epidermal Cyst (mobile under skin)
Inflamed Seborrheic Keratosis (stuck-on appearance)
Lichen Planus (purple, polygonal papules with flat surface)
Miliaria Rubra (heat/overbundling of child)
Pyogenic Granuloma (bleeds easily)
Scabies (burrow, interdigital/groin, family members)
Urticaria
Flat Brown Macule
Actinic/Solar Lentigo (sun-damaged area)
(circumsrcibed flat and
Congenital Nevus (contain hair)
discoloured area)
Cafe-au-Lait (present in childhood, very light brown)
Hyper/hypopigmentation (e.g. posttraumatic, Addison’s)
Freckle (sun-exposed areas, disappears in winter)
Junctional Nevus (regular shape)
Lentigines associated with underlying disorders (LEOPARD, LAMB, Peutz-Jegher’s)
Lentigo Maligna (irregular, varied pigmentation)
Malignant Melanoma (characteristic atypia)
Pigmented Basal Cell Carcinoma
Simple Lentigo (non-sun exposed area, irregular)
Stasis Dermatitis
Viral
Nonviral
(circumscribed collection
• HSV (mouth, genitals)
Acute Contact Dermatitis (e.g. poison ivy)
of free fluid > 1 cm)
• Zoster (dermatomal,painful) Cat-Scratch Disease
• Varicella (generalized, itchy) Dyshydrotic Eczema (sides of fingers/palms/soles)
• Molluscum (umbilicated) Dermatitis Herpetiformis (VERY itchy, gluten history)
• Coxsackie Impetigo
(painful, hand-foot-mouth, summer) Porphyria Cutanea Tarda
(hypertrichosis, heliotrope lesion around eyes,
alcohol ingestion)
Scabies
Bullae
Bullous Impetigo (children, other family members)
(circumscribed collection
Bullous Pemphigoid (tense, lower limb)
of free fluid > 1 cm)
Drug eruption
EM/SJS/TEN (target lesions)
Lupus Erythematosus (American Rheumatology Association (ARA) criteria)
Pemphigus Vulgaris (flaccid, easy bleeding)
Poyphyria Cutanea Tarda (photodistribution, fragile skin, hyperpigmentation)
Dermatitis Herpetiforms (extensor surfaces, symmetrically grouped)
Acute dermatitis
MCCQE 2006 Review Notes
Dermatology – D3
Red Scaling Lesions
Contact Dermatitis (history)
nail pits, Koebner’s)
Vesicles
Viral
(exposure history)
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USEFUL DIFFERENTIAL DIAGNOSES
. . . CONT.
Table 3. Differential Diagnosis by Morphology (continued)
Pustules
Acne (teenager, face/chest/back)
(elevated, contains
Acne Rosacea (forties, telangiectatic, no comedones)
purulent fluid,
Candida (satellite pustules, areas of skin folds)
varying in size)
Dermatophyte infection
Dyshidrotic Eczema (sides of fingers/palms/soles)
Folliculitis (in hair follicle)
Hidradenitis suppurativa
Impetigo (honey-crust)
Sepsis (e.g. staph, gonococcal)
Pustular Psoriasis (psoriasis)
Rosacea
Varicella
(break in the skin that extends
Common: Arterial, Venous, Neurotrophic, Pressure
to the dermis, or deeper)
Cancer (e.g. SCC),Chromosomal (e.g. XXY)
Hemoglobinopathy (e.g. Sickle Cell)
I nflammatory (e.g. RA, SLE, Vasculitis, Raynaud’s)
P yoderma Gangrenosum (e.g. ulcerative colitis, RA)
Infectious (syphilis, TB, tularemia, plague)
Necrobiosis Lipoidica Diabeticorum (DM)
Oral Ulcers
Aphthous
Cancer (SCC/BCC)
Dermatologic Diseases (Lichen Planus, Pemphigus vulgaris)
Iatrogenic (Chemo, Radiation)
Infectious (HSV/HZ, Coxsackie, HIV, CMV, TB, Syphilis, Aspergillosis, Cryptococcosis)
Inflammatory (SLE, Seronegatives, EM/SJS/TEN, allergic stomatitis)
Traumatic
Table 4. Differential Diagnosis by Location
Location
Common
Less Common and Rare
Scalp
psoriasis, folliculitis, pediculosis, tinea, SCC
Pemphigus, DH
Ears
Seborrheic dermatitis, psoriasis, infectious
Fungal infection
eczematoid dermatitis, actinic keratoses
Face
Acne, rosacea, impetigo, contact dermatitis,
Lupus, actinic dermatitis, dermatomyositis,
seborrheic dermatitis, folliculitis,
lentigo maligna melanoma
herpes simplex, BCC, SCC, actinic keratoses,
sebaceous hyperplasia
Eyelids
Contact dermatitis (fingernail polish, hairspray),
seborrheic dermatitis, atopic eczema,
xanthelasma
Posterior Neck
Neurodermatitis (LSC), seborrheic dermatitis, Acne keloidalis in black patients, acanthosis
psoriasis, contact dermatitis
nigricans
Mouth
Aphthae, herpes simplex, geographic tongue,
Syphilis, lichen planus, pemphigus
Axillae
Contact dermatitis, seborrheic dermatitis,
Erythrasma, acanthosis nigricans,
hidradenitis suppurtiva
inverse psoriasis, Fox-Fordyce disease
Chest and Back
tinea versicolour, pityriasis rosea, acne,
Secondary syphilis, Grover’s disease,
seborrheic dermatitis, psoriasis, Herpes Zoster
cherry angioma, BCC, melanoma
Crural Areas
psoriasis, pediculosis, granuloma inguinale,
lichen simplex
Penis
Contact dermatitis, fusospirochetal and Primary and secondary syphilis,
candidal balanitis, chancroid, herpes simplex, balanitis xerotica obliterans, lichen planus
Condylomata (HPV), scabies
Hands
Tinea manis, (one-hand two feet), warts,
erythema multiforme, secondary syphilis (palms)
atopic eczema, psoriasis, actinic
and fungal infection
keratosis, solar lentigo
Cubital Fossae and
Atopic eczema, contact dermatitis
Elbows and Knees
Psoriasis, xanthomas
Atopic ezcema, DH
Legs
Contact dermatitis, stasis dermatitis, ulcers,
leukocytoclastic vasculitis, HSP and other
vasculitidies
Feet
Fungal infection, primary or secondary
Psoriasis, erythema multiforme,
bacterial infection, contact dermatitis,
secondary syphilis (soles),
atopic eczema, warts
acral lentiginous melanoma (soles)
D4 – Dermatology
MCCQE 2006 Review Notes
Ulcer
Uncommon: “CHIP IN ” mnemonic
Seborrheic dermatitis, contact dermatitis,
contact dermatitis
Seborrheic keratosis, dysplastic nevi,
inverse psoriasis
Groin and
Tinea, Candida, bacterial intertrigo, scabies,
Contact dermatitis, dyshydrotic eczema,
Pustular psoriasis, granuloma annulare,
Popliteal Fossae
and prickly heat
nummular eczema, melanoma, ichthyosis
Pyoderma gangrenosum, erythema nodosum,
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COMMON SKIN LESIONS
HYPERKERATOTIC
Seborrheic Keratosis (Senile Keratosis) (see Colour Atlas D8)
definition: benign neoplasm of epidermal cells
epidemiology
• > 30 years, M>F
• autosomal dominant inheritance
• more common with increasing age
differential diagnosis
• solar lentigo
• spreading pigmented actinic keratosis
• pigmented basal cell carcinoma
• malignant melanoma (lentigo maligna, nodular melanoma)
• melanocytic nevi
signs and symptoms
• round/oval, well demarcated discrete waxy papule/plaque, +/– pigment, warty surface,
“stuck on” appearance
• sites: face, trunk, upper extremities
• usually asymptomatic
clinical course
• over time, increase in pigmentation, “stuck on” plaque appears warty, “horny cysts”
investigations
• biopsy only if diagnosis uncertain
management
• no treatment usually needed
• liquid nitrogen for cosmetic reasons
Actinic Keratosis (Solar Keratosis) (see Colour Atlas D19)
definition: premalignant epithalial neoplasm
epidemiology
• middle age and elderly (except in sunny climates)
• M>F, skin phototypes I-III (see Table 1)
• melanin is protective
pathophysiology
• UV radiation damage to keratinocytes (especially UVB)
• pleomorphic keratinocytes, parakeratosis and atypical keratinocytes
differential diagnosis
• chronic cutaneous lupus erythematosus
• Bowen’s Disease
• SCC in situ
• superficial BCC
signs and symptoms
• discrete yellow-brown, scaly patches on a background of sun damaged skin (sand-like on palpation)
• < 1 cm, round/oval
• sites: areas of sun exposure - face (forehead, nose, cheeks,
lips, temples), ears, scalp if bald, neck, forearms, hands, shins
clinical course
• may transform into SCC
management
• 5-FU (fluorouracil) cream applied for 2-3 wks
• liquid nitrogen
• biopsy lesions that are refractory to treatment
Keratoacanthoma (see Colour Atlas D18)
definition
• benign epithelial neoplasm with atypical keratinocytes
epidemiology
• > 50 years, rare under 20 years
• skin phototypes I-III
etiology
• associated with human papilloma virus (HPV)
• associated with UV radiation and chemical carcinogens (tar, pitch, mineral oil)
pathophysiology
• proliferation of atypical keratinocytes in epidermis
differential diagnosis
• squamous cell carcinoma (SCC) (grows slower – months)
signs and symptoms
• red/skin coloured, firm, dome-shaped nodule with central keratin-filled crater
• sites: sun-exposed skin
clinical course
• rapidly grow to ~2.5 cm in 6 weeks, with keratotic plug in centre of nodule by 6 weeks
• attains full size in < 4 months,spontaneously regresses in < 10 months
• disfiguring scar after regression
management
• surgical excision
• curettage and electrocautery
• if on lip treat as SCC
MCCQE 2006 Review Notes
Dermatology – D5
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