Dermatology

Question 1

Why does Staphylococcus aureus cause bullous impetigo and staphylococcal scalded skin syndrome?

Answer 1

S. aureus releases exotoxins (epidermolytic toxins A and B) which break up desmoglein 1

Desmosomes = part of skin cell responsible for adhering to other skin cells

Question 2

What are the causes of erythema multiforme?

Answer 2

1. Infection - HSV (most common), Mycoplasma (most common bacterial), adenovirus, CMV, VZV, hepatitis virus, HIV
2. Medication - NSAIDs, penicillin, anticonvulsants, barbiturates

= hypersensitivity reaction
+/- mucous membrane involvement
Backs of hand/feet -> from limb toward trunk
Upper > lower

‘TARGET’ lesion
Polymorphous = initially macule -> papule -> plaques
(hence ‘multiforme’)

Question 3

What are the causes of erythema nodosum?

Answer 3

1. Disease - IBD, sarcoidosis, collagen vascular or connective tissue disease, spondyloarthropathy, celiac dsiease (rare)
2. Infection - GAS, TB, Mycoplasma pneumoniae, hepatitis, Yersinia, funal
3. Medications - Sulfonamide, phenytoin, OCP

= type of panniculitis (inflam. of subcut fat, without vasculitis) + hypersensitivity reaction

Red lumps to shin/knees/ankle
10 days eruption -> lasts 3-6 weeks

Also: fever, fatigue, aching, conjunctivitis

Question 4

What is dermatitis herpetiformis?

Answer 4

= ITCHY, VESICULAR rash that erupts SYMMETRICALLY on EXTENSOR surface of arms, legs and buttocks

Pathognomonic for celiac disease

‘Herpetiformis’ = tendency for blisters to appear in clusters -> resembling herpes simplex (but NOT caused by it)