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
