6: Skin infections

Question 1

Skin disease in GP vs hospital

Answer 1

GP - 25% infectious

Hospital - 5% infectious

Question 2

S. aureus features

Answer 2

Commensal
Produces:
Panton Valentine Leuocidin toxin
Exfoliative toxin
Enterotoxin
TSST-1

Causes bone, joint and lung infections

Question 3

Types of S.aureus infections in skin

Answer 3

Impetigo = subcorneal layer of epidermis (golden crusting)
Bullous impetigo
Ecthyma = infection of full layer of epidermis
Abcess
Staphylococcus scalded skin syndrome (children under age of 5, due to exfoliative toxin)

Question 4

Treponema Pallidum features

Answer 4

Gram negative
Cause of syphilis
STD
12 million new cases worldwide

Question 5

Stages of syphilis

Answer 5

Sexual contact leads to
Primary (3-8 weeks)
- painless ulcer (genital/oral)

Secondary (6-12 weeks)
- Generalised rash, lymphadenopathy

Latent syphilis - no signs

Tertiary (years later)
Skin/neurological/vascular manifestations

Question 6

Stages of syphilis

Answer 6

Sexual contact leads to
Primary (3-8 weeks)
- painless ulcer aka CHANCRE (genital/oral) which disappears
- Diagnosis: dark filed microscopy

Secondary (6-12 weeks)

• Generalised rash, lymphadenopathy
• Palm and soles involved

Latent syphilis - no signs

Tertiary (years later)

• Skin/neurological/vascular manifestations
• destructive bone lesions
• Gummatous skin lesions
• Thoracic aneurysm
• Neurosyphilis

Can also get congenital syphilis (acquired perinatally) leading to miscarriage, stillbirth, rashes, bone disease, neurological problems

Question 7

Herpes simplex features

Answer 7

HSV 1 = ORAL herpes
HSV 2 = GENITAL herpes

Vesicular rash in oral/genital region but can be in other places (lasts 2 weeks)
Can lead to Eczema herpeticum
Herpes encephalitis (brain)

HSV/VZV have LATENCY i.e. they can go somewhere else and be reactivated

Question 8

Varicella zoster (VZV)

Answer 8

aka chicken pox (clinically unwell)
Mouth/face concentrated rash
Can reactivate causing shingles

Virus lives on in sensory neurones (particularly dorsal root ganglion)
Can get reactivated to cause Herpes zoster aka shingles
(clinically WELL)
- Chickenpox-like rash down one dermatome and doesn’t cross midline
- If it involves face = Opthalmic herpes zoster

Question 9

Organisms causing Superficial skin fungal infections

Answer 9

Dermatophytes (mould)
Trychophyton rubrum - commonest cause of athlete’s foot/nail infections
Grow in KERATIN, long hyphae

Yeasts (e.g. candida)
Grow on warm moist surfaces
single cell/bud

Question 10

Superficial skin fungal diseases

Answer 10

Tinea unguium
Can be caused by either
Infection of nails
Yellow crumbly nails

Tinea capitis (children ONLY, typically afrocarribean)
Kerion - type of tinea capitis, well defined bulky mass

Tinea mannum (hand) - from handling animals

Tinea pedis (foot) (trychophyton rubrum)

Tinea cruris (groins)

Tinea facei (face) - from handling animals

Candida intertrigo - YEAST infection, usually on eczema causing overgrowth

Question 11

Scabies features

Answer 11

Sarcoptes scabei
Burrows in surface of epidermis
Looks like white S with black spot on the end (around 3mm)
Usually in webbing of fingers/toes, around nipples, genital area
After 4 weeks -> allergic reaction to eggs/faeces
Develops into widespread ECZEMA