USMLE - Derm

"Californians Like Girls in String Bikinis"

Stratum Corneum (keratin)

Stratum Lucidum

Stratum Granulosum

Stratum Spinosum (spines = desmosomes)

Stratum Basale (stem cell site)

Holocrine (cell rupture) secretion of sebum associated with hair follicle

Secret sweat

Found Everywhere

Secretes milky viscous fluid

Found in axillae, genitalia, and areolae

Does not become functional until puberty

Malodorous because of bacterial action

Zona Occludens

Prevents paracellular movement of solutes

Claudins and Occludins

Zona Adherens

Below tight junctions

Forms belt connection actin cytoskeletons of adjacent cells

CADherins (Ca dependent ADhesion proteins)

Loss of E cadherin promotes metastasis

Macula Adherens

Structural support

Desmoplakin and Keratin

Autoantibodies –> pemphigus vulgaris

Connexons (channel proteins)

Permit electrical and chemical communication

Connect keratin in basal cells to underlying basement membrane

Integrins in cell bind Laminin in BM

Autoantibodies –> Bullous Pemphigoid

90% are female 14-45. Most common and severe in blacks

Fever, Fatigue, Wt Loss, Libman-Sacks Endocarditis, Hilar adenopathy, Raynaud Phenomenon

Nephritis is common cause of death

Nephritic: DPGN, Nephrotic: Membranous

Verrucous wart-like sterile vegetations on both sides of valve

False + on Syphilis test (RPR/VDRL) due to antiphospholipid Abs which cross react with cardiolipin used in test

ANA (sensitive but not specific)

Anti dsDNA (specific, poor prognosis)

Anti Smith Ab (specific, not prognostic)

Anti Histone Ab (sensitive for drug induced lupus)

“I’m DAMN SHARP”

Immunoglobins (dsDNA, Smith, Phospholipids)

Malar Rash

Discoid Rash, ANA, Mucositis (oropharyngeal ulcers), Neurological disorder

Serositis (pleuritis, pericarditis), Hematologic disorders, Arthritis, Renal disorders, Photosensitivity

Black females

Enlarged bilateral hilar adenopathy or reticular opacities on CXR

↑ ACE levels, ↑ Ca (elevated 1α hydroxylase mediated VitD activation in epithelioid Macs)

Noncaseating Granulomas

“A Red BUG”

Often asymptomatic. Erythema Nodosum, Bell’s Palsey, Epithelial Granulomas containing microscopic Schaumann and Asteroid Bodies, Uveitis

Associated with Restrictive Lung disease (interstitial fibrosis)

Steroids

Excessive fibrosis and collagen deposition throughout body

Commonly sclerosis of skin manifesting as puffy and taut skin w/o wrinkles

Sclerosis of Renal, Pulmonary (most common cause of death), CV, GI systems

75% females

Diffuse vs CREST

Widespread skin involvement

Rapid progression with early visceral involvement

Anti Scl70 Ab (anti DNA topoisomerase I)

Calcinosis, Raynaud’s phenomenon, Esophageal dismotility (b/c of fibrous replacement of muscularis), Sclerodactyly, Telangiectasia

Limited skin involvement (Fingers and Face)

Benign clinical course

Anti Centromere Ab

Flat lesion w/ well circumscribed change in skin color

<5mm

Macule >5mm

Elevated solid skin lesion <5mm

Papule >5mm

Small fluid containing blister <5mm

Large fluid containing blister >5mm

Vesicle containing pus

Transient smooth papule or plaque (Hives)

Flaking off of stratum corneum

Dry exudate

Thickening of stratum corneum

Hyperkeratosis with retention of nuclei in stratum corneum

Separation of epidermal cells

Epidermal hyperplasia (↑ spinosum)

Inflammation of the skin

Normal melanocyte # with ↓ melanin production

| ↓ Tyrosinase activity or failure of neural crest cell migration during development

Hyperpigmentation associated with pregnancy or OCP use

irregular areas of complete depigmentation caused by ↓ in melanocytes

Warts

HPV

Soft, tan colored, cauliflower-like papules

Epidermal hyperplasia, Hyperkeratosis, Koilocytosis

Condyloma Acuminatum on genitals

Common mole

Benign but melanoma can arise in congenital or atypical moles

Intradermal nevi are papular. Junctional nevi are flat macules

Hive

| Pruritic wheal that forms after mast cell degranulation

Freckle

| Normal # of melanocytes with ↑ melanin pigment

Eczema. Pruritic eruptions

Commonly on skin flexures

Associated with other atopic disease (asthma, allergic rhinitis)

Usually starts on the face during infancy and often appears in the antecubital fossae thereafter

Type IV hypersensitivity reaction following exposure to allergen

Lesions occur at site of contact

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 spots from exposed dermal papillae when sclaes are scraped off)

Associated with nail pitting and psoriatic arthritis

Flat, Greasy, Pigmented Squamous Epithelial Proliferation with keratin filled cysts (horn cysts)

Looks stuck on

Head, trunk, extremities

Benign neoplasm

Older persons

Sudden appearance of multiple seborrheic keratoses indicating an underlying malignancy (GI, lymphoid)

IgG Abs against desmoglein 1 +/or 3 (part of desmosome)

If reveals Abs around epidermal cells in reticular or netlike pattern

Acantholysis - Intraepidermal bullae causing flaccid blister involving skin and oral mucosa. + Nikolsky Sign

Separating of epidermis upon manual stroking of skin

| Means that the lesion is intraepidermal

IgG Abs against hemidesmosomes

Linear If

Eosinophils within tense border

Affects skin but not oral mucosa

- Nikolsky sign

Pruritic papules, vesicles, and bullae

Deposits of IgA at tips of dermal papillae

Associated w/ celiac disease

Infections (Mycoplasma pneumoniae, HSV), Drugs (sulfa, β lactams, phenytoin), Cancer, Autoimmune

Presents with macules, papules, vesicles, target lesions (targets with multiple rings and dusky center showing multiple epithelial disruption)

Fever, Bulla, Necrosis, Sloughing off of skin

High mortality rate

Typically 2 mucus membranes are involved. Lesions may appear like targets as seen in erythema multiforme

Adverse drug reaction

More severe form is toxic epidermal necrolysis

Epidermal hyperplasia causing symmetrical hyperpigmented, velvety thickening of skin

Neck and axilla

Hyperinsulinemia (diabetes, obesity, Cushing's) and visceral cancer

Premalignant lesion caused by sun exposure

Small, rough, scaley erythematous or brownish papules or plaques

Risk of squamous cell carcinoma proportional to degree of epithelial dysplasia

Inflammatory lesions of subcutaneous fat

Anterior shins

Sarcoidosis, Coccidioidomycosis, Histoplasmosis, TB, Streptococcal infection, Leprosy, Crohn's Disease

Pruritic, Purple, Polygonal, Planar, Papules and Plaques

Sawtooth infiltrate of lymphocytes at dermal-epidermal junction

HCV

Herald Patch followed days later by Christmas tree distribution. Self-resolving in 6-8 weeks

Multiple plaques with collarette scales

UV irradiation causes DNA mutations inducing apoptosis of keratinocytes

UVA is dominant in tanning and photoaging

UVB is dominant in sunburn

Can lead to impetigo and skin cancers (basal cell carcinoma, squamous cell carcinoma, and melanoma)

Very superficial skin infection

S aureus or S pyogenes

Highly contagious

Honey colored crusting

Bullae caused by S aureus

Spreading infection of dermis and subcutaneous tissues

Acute and painful

S pyogenes or S aureus

Often starts with break in skin from trauma or another infection

Deeper tissue injury

Anaerobic bacteria or S pyogenes. "Flesh eating bacteria"

Crepitus from methane and CO2 production

Bullae and purple colored skin

Exotoxin destroys keratinocyte attachment in the stratum granulosum only

Fever and generalized erythematous rash with sloughing of the upper layers of the epidermis that heals completely

Newborns and children

Exotoxin destroys epidermal-dermal junction

White, painless, plaques on the tongue that cannot be scraped off

EBV

HIV+ pt

Most common skin cancer

Sun exposed areas

Locally invasive but almost never metastasizes

Pink, Pearly nodules commonly w/ telangiectasias, rolled border, central crusting or ulceration

Also appears as nonhealing ulcer with infiltrating growth or a scaling plaque

Palisading nuclei

2nd most common skin cancer

Sun exposure, immunosuppression, arsenic exposure

Face, lower lip, ears, hands

Locally invasive but may spread to lymph nodes and will rarely metastasize

Ulcerative red lesions with frequent scales

Associated with chronic draining sinuses

Keratin pearls

Variant of Actinic Keratosis that grows rapidly (4-6 weeks) and may regress spontaneously over months

Depth of tumor correlates with metastasis

S-100

Sunlight exposure. Fair skinned persons

Asymmetry, Border irregularity, Color variation, Diameter > 6mm, Evolution over time

BRAF kinase mutation. BRAF V600E is metastatic and unresectable.

Excision with appropriately wide margins. BRAF V600E: use Vemurafenib or BRAF kinase inhibitors