Dermatology Flashcards
What would be the likely cause of a edematous papular rash on the lower legs with target lesions and an extensor distribution?
Erythema multiforme. Usually follows infection or new drug. Palms and lips can also be involved.
What would be the likely cause of a purpuric rash on the lower legs with an unwell, febrile patient?
Meningococcal septicaemia.
What would be the likely cause of a rash on the lower legs with purplish flat topped papules.
Lichen planus. Possibly this is autoimmune mediated.
What would be the likely cause of a rash on the lower legs with individual round lesions?
Insect bites - especially if history suggestive.
Cause of rash in meningococcal septicaemia
Vascular occlusion and localised areas of inflammation and necrosis.
The lesions are purpuric (purplish, non-compressible) due to leakage of red blood cells out of damaged vessels into the dermis and sub-cutis.
Progression of rash in meningococcal septicaemia.
The lesions start as red areas and develop rapidly into purple areas, often with a reticulate (network) pattern or an angular, stellate (star-shaped) pattern. Blistering and then ulceration is common as the necrosis develops.
Appearance of lichen planus
The lesions may have a fine white network pattern on the surface – called Wickham’s striae.
May be a white network inside the mouth, usually on the buccal mucosa.
What is the most likely cause of a purplish rash on the lower legs?
Vasculitis.
List causes of purplish lower leg rashes
Cutaneous vasculitis Erythema multiforme Meningococcal septicaemia Infective endocarditis Insect bites Coagulopathy as in myeloma.
What investigations would you do to rule out vasculitis as a cause of a purplish lower leg rash.
U&E - renal damage from vasculitis
LFT - hepatitis cause of vasculitis
Urine microscopy - to confirm dipstick findings
Skin biopsy with immunofluorescence - for vasculitis
ANA, RF - for connective tissue disease cause of vasculitis
ASOTitre (Streptococcal infection) - for infection cause of vasculits
Hepatitis B & C serology - for infection cause of vasculitis
What investigations would you do to rule out infective endocarditis as a cause of purplish lower leg rash?
Chest X ray - Heart size (Inf Endo),
Blood culture if patient generally unwell or with marked pyrexia - infective endocarditis, meningococcus
Common causes of cutaneous vasculitis
Streptococcal infection
Drug reaction, especially analgesics and antibiotics
Collagen diseases (RA, SLE)
Malignancy
Vitiligo
well demarcated patches of depigmented skin
the peripheries tend to be most affected
trauma may precipitate new lesions (Koebner phenomenon)
Conditions associated with vitiligo
type 1 diabetes mellitus Addison's disease autoimmune thyroid disorders pernicious anaemia alopecia areata
Management of vitiligo
sun block for affected areas of skin
camouflage make-up
topical corticosteroids may reverse the changes if applied early
there may also be a role for topical tacrolimus and phototherapy, although caution needs to be exercised with light-skinned patients
What is the difference between lichen planus and lichen sclerosis?
planus: purple, pruritic, papular, polygonal rash on flexor surfaces. Wickham’s striae over surface. Oral involvement common
sclerosus: itchy white spots typically seen on the vulva of elderly women
What drugs causes lichenoid eruptions?
gold
quinine
thiazides
How do you treat lichen planus?
topical steroids are the mainstay of treatment
extensive lichen planus may require oral steroids or immunosuppression
How do you treat cellulitis?
Using flucloxacillin
Acne rosacea
Acne rosacea is a chronic skin disease of unknown aetiology
Features
typically affects nose, cheeks and forehead
flushing is often first symptom
telangiectasia are common
later develops into persistent erythema with papules and pustules
rhinophyma
ocular involvement: blepharitis
Treatment for acne rosacea
opical metronidazole may be used for mild symptoms (i.e. Limited number of papules and pustules, no plaques)
more severe disease is treated with systemic antibiotics e.g. Oxytetracycline
recommend daily application of a high-factor sunscreen
camouflage creams may help conceal redness
laser therapy may be appropriate for patients with prominent telangiectasia
What is the likely cause of a small round patch of hair loss in a 23 yr old man?
Alopecia areata
What is alopecia areata
Alopecia areata is a presumed autoimmune condition causing localised, well demarcated patches of hair loss. At the edge of the hair loss, there may be small, broken ‘exclamation mark’ hairs
Prognosis of alopecia areata
Hair will regrow in 50% of patients by 1 year, and in 80-90% eventually. Careful explanation is therefore sufficient in many patients. Other treatment options include:
topical or intralesional corticosteroids
topical minoxidil
What is the name and vitamin deficiency causing diarrhoea, confusion and eczematous skin
Pellagra, caused by niacin (B3) deficiency
Examples of type 1 hypersensitivity reactions
- Anaphylaxis
* Atopy (e.g. asthma, eczema and hayfever)
Mechanism of type 1 hypersensitivity reaction
Antigen reacts with IgE bound to mast cells
Examples of type 2 hypersensitivity reactions
- Autoimmune haemolytic anaemia
- ITP
- Goodpasture’s syndrome
- Pernicious anaemia
- Acute haemolytic transfusion reactions
- Rheumatic fever
- Pemphigus vulgaris / bullous pemphigoid
Mechanism of type 2 hypersensitivity reaction
IgG or IgM binds to antigen on cell surface
Mechanism of type 3 hypersensitivity reaction
Free antigen and antibody (IgG, IgA) combine
Examples of type 3 hypersensitivity reactions
- Serum sickness
- Systemic lupus erythematosus
- Post-streptococcal glomerulonephritis
- Extrinsic allergic alveolitis (especially acute phase)
Mechanism of type 4 hypersensitivity reaction
T-cell mediated
Examples of type 4 hypersensitivity reactions
- Tuberculosis / tuberculin skin reaction
- Graft versus host disease
- Allergic contact dermatitis
- Scabies
- Extrinsic allergic alveolitis (especially chronic phase)
- Multiple sclerosis
- Guillain-Barre syndrome
Features of necrotising fasciitis
acute onset
painful, erythematous lesion develops
extremely tender over infected tissue
