Common skin infections

Question 1

Describe the skin as a barrier to infection

Answer 1

• stratum corneum (outermost layer of the epidermis) consists of keratinised cells and is a mechanical barrier to infection
• disruption allows penetration of pathogens into underlying tissue and throughout the body via lymphatics and blood vessels (capillary plexus)
• disruption of mechanical barrier causes inflammation (another barrier to infection = good) although this response can be exaggerated in severe infections (= bad)

Question 2

IMPETIGO/SCHOOL SORES/PYODERMA

• Symptoms?
• Causes?
• Pathogenesis?
• Investigation?
• Treatment?

Answer 2

Symptoms: red papules, pustules and plaques on arm/hand/face (sometimes confused w/ herpes)

Cause: Group A Strep (S. pyogenes)

Pathogenesis: infection of superficial skin

Investigation: skin swab (gram stain to confirm S. pyogenes)

Treatment: topical antibiotics (fucidin) or oral (fluclox)

Question 3

Describe the role of venous insufficiency in skin and soft tissue infections

Answer 3

Venous insufficiency is a predisposing factor to cellulitis, erysipelas, chronic venous ulcers and other skin infections.

Question 4

Describe common cellulitis masquaraders

Answer 4

Lipodermatosclerosis (2ndary to venous stasis), erythema nodosum, pyoderma gangrenosum

Important to treat underlying cause - not based on the symptoms, as these can be common between cellulitis and its masquaraders

Question 5

TINEA

• Symptoms?
• Causes?
• Pathogenesis?
• Investigation?
• Treatment?

Answer 5

Symptoms: itchy, burning skin; thick, crumbly, discoloured nails

Causes: dermatophyte infection, many species (most common is T. rubum)

Patho.: fungi invade epidermis and cause inflammation by producing keratinases. Can be at different sites of the body (tinea pedis = feet; tinea corporis = body; tinea cruris = creases; tinea capitis = scalp; tinea unguium = nail; tinea versicolour = mostly trunk hyper/hypopigmentation)

Invest.: skin scraping (from edge of advancing lesion) or nail clipping –> microscopy and culture

Treatment: antifungals

Question 6

PARONYCHIA (bacterial)

• Symptoms?
• Causes?
• Pathogenesis?
• Investigation?
• Treatment?

Answer 6

Symp: painful, red, swollen fingernail

Causes: Staph. aureus

Patho.: soft tissue infection around fingernail from breakdown of protective barrier bw nail and nail fold

Invest.: nil outlined

Treatment: soak w/ warm water, oral antibiotics (augmentin or clindamycin), drainage of pus

Question 7

CHRONIC PARONYCHIA (fungal)

• Symptoms?
• Causes?
• Pathogenesis?
• Investigation?
• Treatment?

Answer 7

Symp: > 6wks of inflammation, pain, swelling

Causes: Candida albicans

Patho: fungal invasion associated with water/damp skin

Invest: nil outlined

Treat: keep dry, warm soaks, topical antifungals

Question 8

DACTYLITIS

• Symptoms?
• Causes?

Answer 8

Symp: sausage shaped, painful, swollen fingers and toes

Causes: Grp A Strep (also seen in sickle cell anaemics)

Question 9

BULLOUS IMPETIGO

• Symptoms?
• Causes?
• Pathogenesis?
• Treatment?

Answer 9

Symp: fluid filled blisters that pop and leave sores

Causes: S. aureus

Patho: S. aureus produces toxins which can spread locally or generally (depending on the host immune system - maternal antibodies). General spread = staph scalded skin syndrome (SSSS)

Treat: fluclox + vancomycin

Question 10

FOLLICULITIS

• Symptoms?
• Causes?
• Pathogenesis?
• Treatment?

Answer 10

Symp: itchy, papules w/ central pustule

Causes: usually S. aureus (eg. folliculitis barbae - think barber –> dry shaving beard spreads S.aureus into tiny cuts), possibly P. aeruginosa (hot tub folliculitis) or Candida

Patho: infection of hair follicles/apocrine glands

Invest: where there is pus, there is swab

Treat: local (saline), topical antibiotics and/or antifungal

Question 11

FURUNCLES/BOILS

• Symptoms?
• Causes?
• Pathogenesis?
• Investigation?
• Treatment?

Answer 11

Symp: deep inflammatory nodule usually in friction/sweaty areas containing follicles (neck, face, underarm/axillae, butt)

Causes: usually S. aureus

Patho: spread of folliculitis to deeper tissues, predisposed by obesity and immunosuppression

Invest: where there is pus, there is swab

Treat: warm soaks, anti-staph antibiotics (fluclox, vanco), prophylaxis for recurrent boils (general hygiene, Staph decolonisation w rifampicin and ciprofloxacin)

Question 12

CARBUNCLE/CLUSTER OF BOILS

• Symptoms?
• Causes?
• Pathogenesis?
• Investigation?
• Treatment?

Answer 12

Symp: recurrent boils, painful discharging lesions, fever, deep infection, usually neck, back or thighs

Causes: usually S. aureus

Patho: Folliculitis spreads to furuncles then forms clusters/carbuncles, can have surrounding infection (cellulitis) and spread to blood (bacteraemia)

Invest: where there is pus, there is swab

Treat: surgical drainage, antibiotics (fluclox + vanco)

Question 13

ERYSIPELAS/RED FACE

• Symptoms?
• Causes?
• Pathogenesis?
• Investigation?
• Treatment?

Answer 13

Symp: red rash w/ clearly defined borders (demarcated borders)

Causes: usually Group A Step.

Patho: superficial bacterial skin infection involving cutaneous lymphatics, predisposed by other factors (tinea, venous insufficiency)

Invest: look for other infections or conditions (tinea etc)

Treat: penicillin

Question 14

CELLULITIS

• Symptoms?
• Causes?
• Pathogenesis?
• Investigation?
• Treatment?

Answer 14

Symp: diffuse spreading erythematous rash (vs erysipelas which has defined borders); inflammation - heat, red, swelling, pain; lymphadenopathy/lymphadenitis, fevers, chills

Causes: S. aureus or beta haemo strep

Patho: acute bacterial infection of skin and soft tissues predisposed by other factors (tinea pedis, skin diseases, leg oedema, immunodeficiency)

Invest: swab blister fluid but could be misleading because of colonisers

Treat: antibiotics (fluclox, cephalexin, clindamycin)