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Type 1 sensitivity
- anaphylactic and atopic
- antigen cross-links IgE on presensitized mast cells
- examples- anaphylaxis, asthma, urticarial drug reaction, local wheal and flare
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Type 2 hypersensitivity
- cytotoxic
- IgM and IgG + complement lead to MAC -> lysis or phagocytosis
- examples- autoimmune hemolytic anemia, Rh disease, Goodpasture's, rheumatic fever
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Type 3 hypersensitivity
- 1. Immune complex: antigen-antibody complement
- examples- polyarteritis nodosa, glomerulonephritides, SLE, RA
- 2. Serum sickness: antibodies to proteins produced --> immune complex forms fix complement
- fever, urticaria, arthralgia, proteinuria, lymphadenopathy 5-10d after exposure
- 3. Arthus reaction: local subacute reaction. Intradermal injection of antigen --> Ag-Ab complexes form
- examples- hypersensitivity pneumonitis, thermophilic actinomycetes
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Type 4 hypersensitivity
- delayed (cell-mediated) type: sensitized T cells release lymphokines
- example- TB skin test, transplant rejection, conact dermatitis
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Seborrheic dermatitis: causative agent, population
- Pityrosporum ovale
- infants- diaper rash, "cradle cap"
- young person- suspect HIV
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Psoriasis: physical features, diagnosis
- psoriatic nails- pitting, "oil spots," onycholysisKoebner's phenomenon- provoked by local irritation
- strep infx can trigger guttate psoriasis, meds (beta blocker, Li, ACEi) can induce
- "sausage digits"; Auspitz sign; on histology Munro's microabscess
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- Erythema Multiforme
- triggers- HSV infx of lip, drugs (sulfa, phenytoin, barbiturates, PCN, NSAIDs), mycoplasmal infx
- target appearance
- palms and soles affected
- could have systemic symptoms
- if severe, can lead to TEN or SJS
- symptomatic treatment
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SJS
- SJS: epidermal separation < 10% BSA. degeneration of basal layer of epidermis
- TEN: >30% BSA. full-thickness eosinophilic epidermal necrosis
- flulike prodrome, erythema multiforme, associated with new drugs (pheytoin, carbamazepine, quinolone, cephalosporin, allopurinol, corticosteroids, NSAIDs)
- + Nikolsky's sign
- histology- degeneration of basal layer epidermis, perivascular mononuclear infiltrate
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Staphylococcal scalded skin syndrome
- children < 6 yrs of age
- infectious etiology
- lose widespread sheets of skin, superficial damage
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- Erythema nodosum
- panniculitis triggered by infection (strep, coccidioides, yerinia, TB), drug rxn, chronic iflammatory dz (sarcoid, Crohn's, UC, Behcet's)
- painful, erythematus nodules on lower legs turns brown or gray
- may have false +VDRL
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Pemphigus vulgaris: characteristics, tx
- age 40-60
- intraepidermal blister
, widespread painful erosions - antibodies against desmoglein
- mucous membrane --> skin involvement
- dx- clinical picture, + Nikolsky's sign, skin bx with immunofluorescence (bx shows acantholysis)
- tx- systemic corticosteroids + steroid sparing agents (mycophenolate mofetil, azathioprine)
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Bullous pephigoid: characteristics, tx
- acquired blistering disease
- age 60-80
- separation at epidermal basement membrane. blisters are stable
- - Nikolsky's sign
- mucous membranes less involved than pemphigus
- dx- clinical picture
- tx- systemic corticosteroids
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Dermatitis herpetiformis: chacteristic, tx
- pruritic papules and vesicles on elbows, knees, buttocks, neck, scalp
- Granular IgA on dermal papillae
- associated with celiac disease
- tx- dapsone, gluten free diet
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HSV
- HSV-1 oral, HSV-2 genital
- cluster of vesicles on erythematous base
- dx- clinical picture, multinucleated giant cells on Tzanck smear
- tx- oral or IV acyclovir
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VZV
- varicella: prurpitic lesion red macules --> grouped vesicles "dewdrop on rose petal"
- at any time all stages of lesions over body. palms, soles spared
- zoster: lesions along dermatome
- preceded by intense local pain
- older pts may have postherpetic neuralgia
- tx- systemic acyclovir, pain control
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Molluscum contagiosum
- poxvirus causes tiny waxy papules with central umbilication
- in children- trunk, extremities, face
- in adults- genitalia, perineal region. if large, think AIDS
- dx- clinical picture, giemsa or wright's stain shows large inclusion or molluscum bodies
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Impetigo: causative agents, types
- group A strep, staph
- common type: pustules, honey-colored crusts usually on face
- bullous type: acral, large stable blisters. almost always caused by S.aureus- can evolve into SSSS
- tx- methicillin, oxacillin, nafcillin
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Erysipelas
- group A strep superficial cellulitis
- small red patch on cheek --> painful raised, shiny plaque (+/- vesicles)
- often history of trauma or pharyngitis
- tx- dicloxacillin, cephalexin or clinda
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Erythrasma
- Corynebacterium
- browinsh-red patch with fine scale, appear in major skin folds
- dx- Wood's light shows coral-red fluorescence, GPR
- tx- erythromycin
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Scarlet fever
- S. pyogenes
- strawberry tongue
- tx- PCN
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Nec Fasciitis
- deep infection along fascial plane- pain --> anesthesia
- S.pyogenes, Clostridium perfringens
- tissue necrosis, putrid discharge, bullae, severe pain, gas production
- dx- radiographs or CT, bx
- tx- surgical emergency. if strep, PCN G (clindamycin 2nd line). metronidazole or 3G ceph for anaerobe
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Tinea Versicolor
- Malassezia furfur
- risk fx- humid, sweaty conditions, oily skin, Cushing's syndrome, immunosuppression
- dx- clinical picture, KOH shows "spaghetti and meatballs" pattern
- tx- topical selenium sulfide
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Gangrene: subtypes
- dry: insufficient blood flow, usually atherosclerosis
- wet: bac infx
- gas: Clostridium perfringens. usually at site of recent injury/surgery- medical emergency
- tx- surgical debridement. hyperbaric O2 for gas gangrene
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Lichen Planus
- chronic inflammatory dermatosis (skin and MM), can be induced by drugs, HCV infx
- purple, polygonal papule, pruritic, penile
- Wickham's striae, Koebner's phenomenon
- dx- histology
- tx- topical corticosteroids for mild dz
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Toxic shock syndrome
- inflammatory response c fever, rash, hypotension, constitutional syndromes
- trunk --> extremities
- need 3+ organ involvement
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- Pityriasis Rosea
- HHV 6 or 7
- hearld patch --> multiple symmetric papules along skin lines with "cigarette paper" scale. "Christmas tree pattern"usually on trunk
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Dermatophyte: causative organisms, treatment
- Microsporum, Trichophyton, Epidermophyton
- risk fx- pets, DM, dec peripheral circulation, immune compromise, athletics
- tx- topical or systemic antifungals. tinea capitis must be treated with systemic drugs
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