Skin Infections Flashcards
2 most common skin pathogens?
- Staph aureus e.g. impetigo
- Strep pyogenes (Strep A)
- bacterial swab used to differentiate
- fluclox, macrolides and tetracyclines cover both
Ecthyma
skin infection characterised by crusted sores beneath which ulcers form - deep form of impetigo, as the same bacteria causing the infection are involved. Ecthyma causes deeper erosions of the skin into the dermis.
Streptococcus pyogenes and Staphylococcus aureus are the bacteria responsible for ecthyma
Cellulitis - features
- staphylococcal or streptococcal
- commonly occurs on the shins, unilateral
- erythema, pain, swelling
- can result in blisters and desquamation
- there may be systemic upset such as fever
- cx: lymphatic damage, chronic swelling, recurrent cellulitis (consider ppx penicillin)
Cellulitis - treatment
- use Eron classification for admission (1 to 4 - 1 being no systemic upset and 4 high risk of sepsis)
- flucloxacillin 10-14 days as first-line treatment for mild/moderate cellulitis. Macrolides (in pregnancy) or doxycyline for patients allergic to penicillin.
- NICE: severe cellulitis should be offered co-amoxiclav, cefuroxime, clindamycin or ceftriaxone
Erysipelas
Superficial form of cellulitis - affects the upper dermis and extends into the superficial cutaneous lymphatics. It is also known as St Anthony’s fire due to the intense rash associated with it.
- tends to be unilateral, beefy red plaque
- may feel systemically unwell - could check inflammatory markers
- almost all erysipelas is caused by Group A Strep
Staphylococcal scalded skin syndrome (SSSS)
Red blistering skin that looks like a burn or scald, hence its name. SSSS is caused by the release of two exotoxins (epidermolytic toxins A and B) from toxigenic strains of Stap aureus.
- usually young children, very unwell
- need supportive treatment and IV Abx
Hypersensitivity to Strep antigen? DDx
- erythema nodosum*
- guttate psoriasis
- vasculitis e.g. HSP
- glomerulonephritis
- scarlet fever
- rheumatic fever
*can also be linked to IBD, sarcoidosis, Bhecet’s, TB, pregnancy, drugs (sulphonamides, OCP)
Necrotising Fasciitis
- type 1 is caused by mixed anaerobes and aerobes in diabetics. (most common type)
- type 2 is caused by Streptococcus pyogenes
- type 3 often post-surgery
- acute onset, painful, erythematous lesion develops
- often presents as rapidly worsening cellulitis
- extremely tender over infected tissue
- really unwell and signs of shock
Management
- urgent surgical referral debridement (remove all necrotic tissue)
- fluids, intravenous antibiotics
Erythema Multiforme
- hypersensitivity reaction which is most commonly triggered by infections (most common is HSV)
- target lesions*, initially seen on the back of the hands / feet before spreading to the torso / upper limbs > lower limbs
- pruritus is occasionally seen and is usually mild
- other causes: some Abx, SLE, sarcoidosis, mycoplasma pneumonia (dx: cold agglutin test and also check bloods for haem anaemia)
- can also affect mucosa e.g. lips, eyes
*three concentric colour zones with darker centre, pale raised middle (due to oedema) and red outer ring
Tinea (ringworm)
Tinea is a term given to dermatophyte fungal infections. Three main types of infection are described depending on what part of the body is infected:
- tinea capitis - scalp*
- tinea corporis - trunk, legs or arms
- tinea pedis - feet
- Well-defined annular, erythematous lesions that scale +/- pustules and papules
- Dx: confirmed by microscopy and culture of skin scrapings
- May be treated with topical rx - Terbinafine cream (Lamisil) or topical miconazole; Or oral itriconazole, fluconazole
*a cause of scarring alopecia mainly seen in children;
if untreated a raised, pustular, spongy/boggy mass called a kerion may form
Fungal Nail infection
Onychomycosis is fungal infection of the nails. This may be caused by
- dermatophytes - accounts for 90% of cases
- yeasts - such as Candida
- non-dermatophyte moulds
- thickened, rough, opaque nails
- exclude psoriasis and linchen planus
- Ix: nail clippings; scrapings of the affected nail
Management:
- dermatophyte: oral terbinafine or oral itriconazole
- candida: topical for mild, or oral itriconazole
Scabies
Mite Sarcoptes scabiei and is spread by prolonged skin contact. It typically affects children. The scabies mite burrows into the skin, laying its eggs in the stratum corneum. The intense pruritus associated with scabies is due to a delayed-type IV hypersensitivity
- widespread pruritus
- linear burrows on the side of fingers, interdigital webs and flexor aspects of the wrist
- scalp usually spared except in a few cases
- secondary features are seen due to scratching: excoriation, infection
(pathgnominic sign = penile papules)
Management
- permethrin 5% is first-line (on whole skin surface)
- malathion 0.5% is second-line
- avoid close physical contact with others and all household and close physical contacts should be treated at the same time, even if asymptomatic
- pruritus persists for up to 4-6 weeks post eradication
Head Lice
‘Pediculosis Capitis’ (parasitic insect) or ‘nits’
The eggs are glued to the hair, close to the scalp and hatch in 7 to 10 days. Nits are the empty egg shells and are white and shiny. They cannot jump, fly or swim! When newly infected, itching and scratching on the scalp occurs 2 to 3 weeks after infection.
Management
- wet combing
- dimeticone
Gas gangrene
Also known as myonecrosis. The causative organism is typically Clostridium perfringens. It is important to note that having a peripheral vascular disease increases the risk of developing gangrene of all causes. C perfringens is a Gram-positive spore-forming bacillus.
features include tender, oedematous skin with haemorrhagic blebs and bullae. Crepitus may present on palpation
