42. Dermatology Flashcards
What are the causes of eczema?
Hygiene hypothesis
- Suppresses the natural development of Th1 predominant immune response
- Promotes a Th2 dominant or allergic response
Genetics
Outline the pathophysiology of eczema
Two hypotheses:
1) Inside-out - Immunological disturbance causes IgE mediated sensitisation, epithelial barrier dysfunction is secondary
2) Outside-in - Epidermal barrier dysfunction allows irritants and allergens into the skin, with immunological disturbance secondary
= immune dysfunction –> itch –> scratch –> leaky skin barrier –> inflam –> immune dysfunction
What are the types of eczema?
Atopic dermatitis (allergic disease - itchy rash is particularly noticeable on head and scalp, neck, inside of elbows, behind knees, and buttocks)
Contact dermatitis
- Allergic - hypersensitivity reaction in the skin
- Irritant contact dermatitis - direct reaction
Seborrhoeic dermatitis - dry or greasy peeling of the scalp, eyebrows, and face, and sometimes trunk
- Newborn = thick, yellow, crusty scalp rash called cradle cap
Dyshidrosis = palms, soles, sides of fingers/toes (worse in warm weather)
Discoid = round spots of oozing or dry rash, with clear boundaries, often on lower legs (worse in winter)
List the signs and symptoms of eczema
Small lesions - entire body
Itchiness
Red skin
Rash
Swelling
Blisters
Thickened skin
Oozing
Scaring
What investigations should be performed if eczema is suspected?
Clinical Dx
Skin biopsy
Patch testing (allergic contact dermatitis)
How is eczema correctly managed?
Lifestyle = bathing once or more daily in warm water, avoid soap
Moisturisers = oil based not water (zerobase)
Topical corticosteroids
Immunosupressants - pimecrolimus and tacrolimus (require regular blood test monitoring)
Antihistamine - reduce nighttime scratching
Abx (infection)
Avoid allergen/irritant
Outline the pathophysiology of impetigo
Involves superficial layers of skin
Spread via direct skin-to-skin contact
Duration - < 3 weeks
What are the signs and symptoms of impetigo?
Often begins as red sore near the nose or mouth, painful itchy yellowish crusts, lymphadenopathy
How should impetigo be investigated?
Clinical diagnosis
How should impetigo be managed?
Abx - topical = mupirocin, fusidic acid, oral = cephalexin
What is staph scaled skin syndrome, its presentation and a DDx?
Staph produces an exfoliative toxin that causes the outer layers of skin to blister and peel, as if they’ve been doused with a hot liquid
Most common in children under 6
S+S = fever, irritability, widespread erythema, within 24-48h fluid-filled blisters form; rupture easily, leaving an area that looks like a burn, tissue paper-like wrinkling of the skin, Nikolsky sign
DDx = drug hypersensitivity, viral exanthemas, scarlet fever, thermal burns, genetic bullous diseases (epidermolysis bullosa), acquired bullous diseases (pemphigus vulgaris, bullous pemphigoid), and toxic epidermal necrolysis
Outline the aetiology and pathophysiology of urticaria
Aetiology = foods, drugs, cosmetics, soaps, infections, insect bites, stings, latex, undue skin pressure, cold, or heat, emotional stress, exercise
Path = allergic reaction
How does urticaria present?
Batches of red or skin-coloured welts (wheals) anywhere on the body
Pruritus
Angioedema - lips, eyelids, inside the throat
S+S flare with triggers such as heat, exercise and stress
How should suspected urticaria be Ix?
Investigations are not usually required for the diagnosis of urticaria
Bloods = FBC, ESR, CRP
Flare up diary
Skin prick testing
Describe the ideal management for urticaria
Antihistamines
Histamine (H-2) blockers - ranitidine
Prednisone
Topical tricyclic antidepressant doxepin - relieve itching
Chronic = omalizumab, immunosuppressants
What is a DDx for urticaria?
Atopic eczema
Contact dermatitis
Chronic pruritus
Erythema multiforme minor
Insect bite or sting
Urticarial vasculitis
What is the aetiology and pathophysiology of varicella?
Aetiology = varicella zoster virus (VZV)
Path =
How does varicella present?
Small, erythematous macules appear on the scalp, face, trunk, and proximal limbs, which progress over 12–14h to papules, clear vesicles (which are intensely itchy), and pustules
Crusting occurs usually within 5d of the onset of the rash, and crusts fall off after 1–2w
Headache, loss of appetite, tiredness, fever
Onset = 10–21 days after exposure
Duration = 5–7 days
How should suspected chickenpox be investigated?
In most cases, the diagnosis can be made clinically from the characteristic chickenpox rash. If there is doubt, a history of recent exposure to chickenpox (or shingles), or cases occurring in close contacts, may help confirm the diagnosis
Outline the management of a varicella infection
Topical calamine lotion - alleviate itch
Chlorphenamine - itch associated with chickenpox for people 1 year of age or older.
Paracetamol - if pain or fever are causing distress
Oral acyclovir - for those who presents within 24 hours of rash onset
Outline a DDx for chickenpox
Other vesicular viral rashes, such as:
- Herpes simplex (not usually disseminated)
- Herpes zoster (usually unilateral and localized to dermatomes)
- Hand, foot, and mouth disease (Coxsackie virus)
Discuss the aetiology and pathophysiology of viral exanthums
Aetiology = enteroviruses, adenovirus, chickenpox, measles, rubella, mononucleosis
Path = eruptive skin rash that is often related to a viral infection
How does viral exanthums present?
Fatigue and irritability one to two days before the rash begins
Itchy rash on the trunk, face, under the armpits, on the upper arms and legs, and inside the mouth
Fever
Feeling ill
Decreased appetite
Muscle and/or joint pain
Cough or runny nose
How should suspected viral exanthums be Ix?
Measles = immunoglobulin M (IgM) antibody
Rubella = IgM/G assays
Varicella Zoster = clinical dx
Record if: - Central or peripheral - Dermatomal distribution - Extensor surfaces - Mucosal involvement Features: - Colour - Blanching or non-blanching - Palpability - Presence of petechiae
