-
Macule
- Flat lesion with well-circumscribed change in skin color
- <5mm
- Example: freckle, labial macule
-
Patch
- Macule > 5mm
- Large birthmark (congenital nevus)
-
Papule
- Elevated solid skin lesion
- <5mm
- Mole (nevus), acne
-
Plaque
-
Vesicle
- Small fluid-containing blister
- <5mm
- Chickenpox (varicella), shingles (zoster)
-
Bulla
- Large fluid-containing blister
- >5mm
- Bollous pemphigoid
-
Pustule
- Vesicle containing pus
- Pustular psoriasis
-
Wheal
- Transient smooth papule or plaque
- Hives (urticaria)
-
Scale
- Flaking off of stratum corneum
- Eczema, psoriasis, SCC
-
Crust
-
Hyperkeratosis
- ↑ thickness of stratum corneum
- Psoriasis
-
Parakeratosis
- Hyperkeratosis with retention of nuclei in stratum corneum
- Psoriasis
-
Acantholysis
- Separation of epidermal cells
- Pemphigus vulgaris
-
Acanthosis
- Epidermal hyperplasia (↑ spinosum)
- Acanthosis nigricans
-
Dermatitis
- Inflammation of the skin
- Atopic dermatitis
-
Albinism
- Normal melanocyte number
- ↓ melanin production due to ↓ tyrosinase activity
- Also caused by failure of neural crest cell migration during development
-
Melasma (chloasma)
- Hyperpigmentation associated with pregnancy
- "mask of pregnancy"
- or OCP use
-
 Vitiligo
- Irregular areas of complete depigmentation
- Caused by ↓ in melanocytes
-
Verrucae
- Warts - caused by HPV
- Soft, tan-colored, cauliflower-like papules
- Epidermal hyperplasia
- hyperkeratosis
- Koilocytosis
- Condyloma acuminatum on genetals:
-
Melanocytic nevus
- Common mole
- Benign, but melanoma can arise in congenital or atypical moles
- Intradermal nevi are papular:
 - Junctional nevi are flat macules:
-
Urticaria
- Hives
- Pruritic wheals that form after mast cell degranulation
-
Ephelis
- Freckle
- Normal number of melanocytes
- ↑ melanin pigment
-
Atopic dermatitis
eczema
- Pruritic eruption, commonly on skin flexures
- Associations: asthma, allergic rhinitis
- Starts on the face in infancy;
 - antecubital fossae thereafter
-
Allergic contact dermatitis
- Type IV hypersensitivity reaction that follows exposure to allergen
- Lesions occur at site of contact
- nickel:
 - poison ivy
- neomycin:
-
Psoriasis
- Papules and plaques with silvery scaling
- knees and elbows
- Acanthosis with parakeratotic scaling (nuclei still in stratum corneum)
- ↑ stratum spinosum
- ↓ stratum granulosum
- Auspitz sign: pinpoint bleeding from exposure of dermal papillae when scales are scraped off
 - Associated with nail pitting and psoriatic arthritis
-
Seborrheic keratosis
- Flat, greasy, pigmented squamous epithelial proliferation with keratin-filled cysts (horn cysts)
 - Looks "stuck on":
 - Lesions occur on head, trunk, extremities
- Common benign neoplasm of older people
- Leser-Trélat sign: sudden appearance of multiple seborrheic keratoses, indicating an underlying malignancy (GI, lymphoid)
-
Blistering skin disorserders
- Pemphigus vulgaris
- Bullous pemphigoid
- Dermatitis herpetiformis
- Erythema multiforme
- Stevens-Johnson syndrome
-
Pemphigus vulgaris
- Autoimmune skin disorder (potentially fatal)
- IgG antibody against desmoglein 3 (1 and/or 3) - part of desmosomes (needed for cell adhesion)
- IF reveals antibodiese around epidermal cells in a reticular or netlike pattern
- Acantholysis - intraepidermal bullae causing flaccid blisters involving skin and oral mucosa
- Positive Nikolsky's sign (separation of epidermis upon manual stroking of skin)
-
Bullous pemphigoid
- Autoimmune disorder
- IgG antibody against hemidesmosomes (epidermal basement membrane)
- **Antibodies are bullow the epidermis
- IF shows linear depositis of IgG
- Eosinophils within tense blisters
- Less severe than pemphigus vulgaris; spares oral mucosa
- Negative Nikolsky's sign
-
Dermatitis herpetiformis
- Pruritic papules, vesicles, and bullae
- Depositis of IgA at the tips of dermal papillae
- Associated with celiac disease
-
Erythema multiforme
- Presentation: multiple types of lesions
- -macules
- -papules
- -vesicles
- -target lesions
 - Associated with infections (e.g., Mycoplasma pneumoniae, HSV), drugs (sulfa, β-lactams, phenytoin), cancers, autoimmune disease
-
Stevens-Johnson syndrome
- Presentation: fever, bulla formation and necrosis, sloughing of skin, high mortality rate
- Typically 2 mucus membranes are involved
- Skin lesions may appear like targets
- Associated with: adverse drug reaction
- Toxic epidermal necrolysis: more severe >30% of body surface area involved
-
Acanthosis nigricans
- Epidermal hyperplasia causing symmetrical hyperpigmented, velvety thickening of skin
- neck or in axilla
- Associated with hyperinsulinemia (diabetes, obesity, cushing's syndrome), visceral malignancy
-
Actinic keratosis
- Premalignant lesions caused by sun exposure
- Small, rough, erythematous or brownish papules or plaques
- Risk of squamous cell carcinoma is proportional to degree of epthelial dysplasia
-
Erythema nodosum
- Inflammatory lesion of subcutaneous fat
- anterior shins
- Associated with sarcoidsosis, coccidioidomycosis, histoplasmosis, TB, streptococcal infections, leprosy, Crohn's disease
-
Lichen Planus
- Pruritic, Purple, Polygonal, Planar Papules and Plaques
- Sawtooth infiltrate of lymphocytes at dermal-epidermal junction
- Associated with hepatitis C
-
Pityriasis rosea
- "Herald patch" followed days later by "christmas tree" distribution
- Multiple plaques with collarette scale
- Self-resolving in 6-8 weeks
-
Sunburn
- UV irradiation causes DNA mutations, inducing apoptosis of keratinocytes
- UVA is dominant in tanning and photoaging
- UVB in sunburn
- Can lead to impetigo and skin cancer (basal, squamous, melanoma)
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