Dermatology — USMLE Step 2 CK Notes

Pemphigus Vulgaris (autoimmune) —-> deadly: AutoAb to desmosomes: IgG

Flaccid bullae and ulcers

Mucosal erosions + Nikolsky sign: separation of epidermis by light friction

Acantholysis (not seen in B Pemphigoid)

Row of Tombstone cells still attached to BM via hemidesmosomes

Immunofluorescence: Netlike intercellular IgG and C3 deposits

Tx: Systemic glucocorticoids; corticosteroid sparing agents and aggressive wound care

Bulbous Pemphigoid: Tense Bullae on erythematous base: hemidesmosomes

65 most common

Increased incidence in those with malignancy or neuro disorders (eg Parkinson’s; MS)

Pre-bulbous Prodrome common: urticarial or eczematous lesions

Linear IgG Abs against hemidesmosome and BM zone: bullous pemphigoid Ags 1&2

Subepidermal cleavage; no acantholysis

Dx via biopsy

Immunofluorecence: linear IgG and C3 deposits along BM

Tx: high potency topical glucocorticoid eg Clobestasol

Systemic glucocorticoids if topical impractical

Epidermolysis Bullosa

Group of inherited disorders characterised by epithelial fragility triggered by minor trauma

Friction induced blisters at palms and soles

Chronic thickening of feet but no scars

Oral blisters when bottle feeding

Seborrheic Dermatitis: yellow and greasy looking scales

Associated with CNS disorders esp Parkinson’s as well as HIV

Most common first year of life then age 30-60

Inflamm disease of scalp (dandruff), face, chest, umbilicus and intertriginous areas (diaper)

—-> areas with numerous sebaceous glands but sebum production normal

Pruritic, erythematous plaques

Tx: Topical antifungals eg ketoconazole, selenium sulfide

—->> Malassezia spp thought to play a role

Associated with Blepharitis

Seborrheic Keratosis: Stuck on appearance

Benign proliferation of immature keratinocytes

Age >50

Velvety/greasy surface

Sudden appearance of multiple SKs —-> Leser-Trelat sign (GI Cancer)

Rash involving palms and soles:

Measles; Kawasaki; TSS; Syphilis; Rocky Mountain; Hand Foot n Mouth

Acne Vulgaris

Comedonal Acne: Topical retinoids/salicylic acid

Inflammatory Acne:

Mild: Topical retinoids with benzoyl peroxide

Moderate: Add topical antibiotics (erythromycin, Clindamycin)

Severe: Add oral antibiotics

Nodular (cystic) Acne: all 3 topical -> oral isotretinoin

Moderate: Topical retinoids with benzoyl peroxide W topical antibiotics

Severe: Add oral antibiotics

Refractory: Oral isotretinoin

NB once oral isotretinoin tx starts all tetracycline use ceases

—> concurrent use has risk of Idiopathic Intracranial HTN

Side Effects of Oral Isotretinoin

Teratogenic

Hyperlipidaemia

Chelates; dry skin/mouth/eyes

Myalgia

Pseudo motor cerebri (esp w concurrent use of tetracyclines)

Retinoids inhibit keratinisation

—-> loosen keratin plugs of comedomes and facilitate expulsion

Also reduce size of sebaceous glands and inhibit sebum production

Drug induced Acne:

Back, upper arms and shoulders w/o comedones

Commonly d/t systemic glucocorticoids

Tetracyclines are a v common cause of phototoxic drug reaction

—> d/t ROS production

Sx resemble common (exaggerated) sunburn: erythema, pain and bullae/vesicles

Others: Antipsychotics; Furosemide, hydrochlorothiazide, Amiodarone, promethazine

Rosacea: Topical metronidazole/erythromycin 4 Primary manifestations: Most have aspects of multiple manifestations

Erythematotelangiectatic rosacea

Papulopustular rosacea: resembles acne

Phymatous rosacea

Ocular rosacea: Can lead to vision loss

Tx: Ocular lubricants; Severe cases may need immunosuppressants:

General Tx: Second line: Oral tetracyclines; ivermectin

Pityriasis Rosea

Numerous small, oval scaly plaques

Herald patch with Christmas Tree distribution

Typically occurs on trunk and proximal extremities

Children and young adults

Typically resolves within 6 wks

Nummular Eczema

Middle aged and older ppl

Idiopathic

Characteristic round, pruritic, scaly plaques that would fit under large coin

Tx: Topical glucocorticoids

Acute palmoplantar (dyshidrotic) eczema: Recurrent, pruritic rash

Deep seated vesicles that preferentially affect palms, soles and sides of digits

Complications: Desquamation, chronic dermatitis, secondary infection

Tx: emollients, High potency topical corticosteroids eg bethamethasone

Avoid irritants and protect from cold/wet conditions

Plaque PSORIASIS (psoriasis is T cell mediated keratinocytes proliferation) Well defined erythematous plaques w silvery scale

Extensor surfaces (knees, elbows), hands (dorsum), scalp, back, nail plates

Kobner phenomenon: lesions at site of injury

Can be triggered by

Infections: HIV and GAS (also guttate psoriasis)

Medications: propranolol, Indomethacin; antimalarials and glucocorticoid withdrawal

Extradermal: Nail changes (eg oncholysis/pitting); Conjunctivitis, uveitis; Psoriatic arthritis

Tx: Topical: High potency glucocorticoids, Vit D Analogs, tar, retinoids, calcineurin Is

Tazarotene

UV/Phototherapy

Systemic: Methotrexate, Calcineurin Is, Retinoids, Apremilast, biological agents

Psoriasis only mildy itchy! ## Auspitz Sign

Pseudofolliculitis barbae

Penetration of hair shaft into interfollicular skin

Most prevalent in black men d/t tightly curled facial hair

Tx: discontinue shaving; adjust shaving routine

Complications: hyperpigmentation S, secondary bacterial infection, keloids

Dermatofibroma: Legs -> dimpling in centre when area pinched

D/t fibroblast proliferation

==> isolated or multiple lesions, most commonly on legs

Nontender, firm, hyperpigmented nodules <1 cm in diameter

Epidermoid (inclusion) Cyst: Commonly on palmer surface of digits

Small, freely mobile nodules with central punctum

Can occur anywhere

Cheese like substance may be expressed intermittently

Resolve spontaneously

Ganglion cyst

Most common in those with underlying joint disease/prev injury

Most common at wrist

Mucinous fluid filled —->> Transilluminates

Often communicate with underlying joint via hollow pedicel

Most resolve spontaneously

Ichthyosis (fish) vulgaris

Inherited condition of chronic diffuse dermal scaling

Mutations in filaggrin gene

Skin appears dry and rough w horny plates resembling fish/reptile scales

Worsens later in life and winter (decreased ambient humidity)

Tx: Emollients, keratolytics (coal tar, salicylic acid) and topical retinoids

Necrobiosis lipoidica

Confluent annular lesions w yellow-brown hue

Dilated bvs and epidermal atrophy

Typically affects pretibial skin in pts w DM

Leukoplakia —-> Erythroplakia (red, raised lesion) ——>> malignancy

Livedo Reticularis

Transient red/purplish blotchy or latticelike rash

Primarily affects legs

D/t obstruction; vasospasm or sluggish flow in superficial venules

Often benign and seen in healthy F during cold weather

Can be a sign of vasculitis (polyarteritis nodosa; SLE) or

Vasooccluisve disorder ( cholesterol embolism; antiphospholipid syn; cryoglobulinaemia)

Keratosis pilaris: posterior surface of upper arm

Retained keratin plugs in hair follicles

Painless papules, rough skin and mottled perifollicular erythema, pruritus poss/asymp

Exacerbations in cold dry weather

Tx: Emollients and topical keratolytics (salicylic acid, urea)

Milaria: Heat Rash

D/t blockage of eccrine glands

Pyoderma Gangrenosum: IBD, Inflamm disorders eg RA and malignancy

Tx: Gluocorticoids

Basal Cell Carcinoma: head and neck Pink, pearly-white, almost translucent dome-shaped nodule or papule

Overlying telangiectasias

Raised or rolled border

Commonly ulcerate, bleed, and crust in the center (a non-healing ulcer)

Dx: Shave or punch biopsy then surgical removal (Mohs) if on face

Surgical excision w narrow margin

Squamous Cell Carcinoma: scaly

Actinic keratosis is precursor lesion (tx w 5FU or excision) —> sun exposed areas

Most common cancer of oral cavity RF: Sun/UV; IR; Immunosuppression; Chronic scar/wound/burn

Scaly, shiny plaques/nodules +/- hyperkeratosis/ulceration

Neurological signs if perineural invasion

SCC in situ (Bowen): slow growing, red, erythematous scaly patches/plaques

—-> confined to epidermis

Dx: Excisional Biopsy w narrow (3mm) margin (dysplastic/anaplastic keratinocytes)

Keratoacanthoma |(variant of low grade SCC) Rapidly growing nodule w ulceration and keratin plug

Seen in fair skinned pts; UV exposure

May resemble/progress to SCC

Frequently regress and resolve spontaneously

Management: excisional biopsy and complete removal

Melanoma

Superficial spreading (best prog, most common)

Nodular (poor prog)

Acrolintiginous (palms, soles, mucous membranes in darker races).

Lentigo Maligna (head and neck, good prog)

Need full thickness biopsy b/c depth is #1 prog

High dose IFN or IL2 may help

Surgical excision w WIDE margin

Nail melanoma: Melanoma arising from nail matrix

Form longitudinal bands in nail plate (longitudinal melanoychia)

Unpigmented melanomas also poss: nodules/irregularities of nail bed

Longitudinal melanoychia that involves multiple nails, stable over years or <3mm wide

=====> usually benign (observer and regular follow up)

Angiosarcoma

Derived from internal lining of bvs or lymphatic vessels

Secondary to breast cancer therapy typically confined to skin

—-> poor px as high grade; lymphoedema often present

Can occur anywhere

RF: Localised radiation

Erysipelas: GAS

Cellulitis (nonpurulent): GAS and MSSA

Cellulitis (purulent)

MSSA and MRSA

Folliculitis

Furuncles: Folliculitis —->> dermis —->> abscess

Carbuncle: Multiple Furuncles

Tx to cover all cellulitis: cephalexin

Amoxicillin covers GAS (Clavulanate added for anaerobic cover)

Nafcillin covers MSSA

Lymphangitis: Tx: cephalexin

Spread of cutaneous injury

Tender erythematous streaks proximal to wound

Tender LAD (lymphadenitis)

Systemic sx

GAS and MSSA

Herpetic Whitlow: Grouped vesicles

Perianal Streptococcus: Painful whilst stooling

School aged

Bright, sharply demarcated erythema over perianal/perineal area; Pruritus

Scarlet Fever: GAS

Fever, palatal petechiae and sandpaper texture rash; strawberry tongue

Typically starts in skin fold and spreads to trunk and extremities

Rare in <3 yrs

Tx: PCN

Toxic Epidermal Necrolysis

30% body surface area

Skin blistering and erosion

Typically triggered by medication

Nikolsky sign + (gentle P on skin surface causes detachment of superficial layer)

Mucous membrane involvement

Staph Scalded Skin Syndrome

Epidermal shedding (Nikolsky sign)—> exposes underlying erythematous (scalded) skin

Generalised erythema w Fever, irritability

—>>> flaccid blisters predominantly in flexor areas exposed to mechanical P (axilla, groin)

No mucous membrane involvement (although perioral crusting can occur)

Tx: Nafcillin/vancomycin and supportive wound care

Toxic Shock syndrome

Associated with tampons; nasal packing (nose bleed) and post surgery infections

Sx develop within 2-3 days:

High fever, Hypotension

Diffuse macular erythroderma

Skin desquamation inc palms and soles 1-2 wks post illness

Multisystem involvement: 3 or more systems

GI: V and/or D; Muscular: Severe myalgia or elevated CK

Mucous membrane hyperaemia; Renal: BUN or Cr >1-2 x upper limit

Haematological (low Plts): leukocytosis may be absent

Liver (ALT, AST and total Bilirubin >2x upper limit)

CNS: Altered mentation w/o focal neurological signs

MCC cause of death is ARDS

Tx: Clindamycin helps inhibit exfoliative toxin production

DDX: Meningococcemia

—->> Petechial rash that progresses to ecchymosis, bullae, vesicles and ultimately

————->> gangrenous necrosis

Intertrigo

Inflamm condition involving occluded skin surfaces eg axilla, groin, folds

MCC is Candida spp (Staph can cause)

— satellite lesions if candida (vesicles, papules, pustules) nr primary infection

Dx clinical w KOH prep to confirm

Candida shows as pseudohyphae with budding yeast forms

Tx: Topical nystatin/miconazole w good skin hygiene and drying

Tinea Cruris

Annular lesions w partial central clearing (may be absent) and scaly, raised border

Caused by several diff dermatophytes —> Septate hyphae on KOH

Chronic Cutaneous Lupus erythematosus

Most common form is discoid lupus erythematosus

Can occur independently of SLE but often progresses to SLE

Chronic scaly irreg erythematous plaques and central hypopigmentation surrounded by

hyperpigmentation

Sun exposed regions of head and neck —> often also chest and arms

Lesions slowly expand over months to years —> dermal atrophy and scarring

Rash often extends to hair follicles —> scarring alopecia

Tinea Versicolor

Malassezia globosa

Spaghetti and meatballs appearance on KOH

Worse in summer —> tanning of surrounding skin makes it obvious

Tx: Selenium Sulfide/ketoconazole