Bacterial Infections

Impetigo

•    Superficial infection, usually in children

•    Golden ("honey-coloured") crusts

•    Non-bullous form: Staphylococcus aureus (most common) and Streptococcus pyogenes

•    Bullous form: always S. aureus (exfoliative toxin)

•    Treatment:

o    Topical fusidic acid (localized)

o    Oral flucloxacillin if widespread

Erysipelas

•    Infection of superficial dermis and lymphatics

•    Raised, sharply demarcated, bright red

•    Common on face and lower limbs

•    Group A Streptococcus (S. pyogenes)

•    Treatment: oral or IV penicillin (flucloxacillin)

Cellulitis

•    Deeper dermal and subcutaneous tissue infection

•    Ill-defined, diffuse erythema

•    Often unilateral lower limb

•    Risk factors: breaks in skin, lymphoedema, diabetes

•    Treatment: oral or IV flucloxacillin (or clindamycin if pen-allergic)

Viral Infections

Herpes Simplex Virus (HSV)

•    Grouped vesicles on erythematous base

•    Painful

•    Type 1: oral/labial

•    Type 2: genital

•    Recurrences common, triggered by stress, illness

Varicella Zoster Virus (VZV)

•    Primary infection: chickenpox → diffuse vesicular rash

•    Reactivation: shingles (herpes zoster)

o    Dermatomal, unilateral

o    Can cause postherpetic neuralgia

•    Treatment:

o    Oral aciclovir within 72 hours for shingles

Molluscum Contagiosum

•    Umbilicated, dome-shaped papules

•    Poxvirus

•    Common in children, immunosuppressed adults (e.g., HIV)

•    Spontaneous resolution, may last months

Fungal Infections

Dermatophyte infections (tinea)

•    Annular ("ringworm") lesions with central clearing and active edge

•    Locations:

o    Tinea corporis (body)

o    Tinea capitis (scalp)

o    Tinea pedis (athlete's foot)

o    Tinea unguium (nails; onychomycosis)

•    Diagnosis: KOH microscopy, fungal culture

•    Treatment:

o    Topical azoles (skin)

o    Oral terbinafine or itraconazole (nails, scalp)

Pityriasis Versicolor

•    Malassezia (Pityrosporum) yeast

•    Hypo- or hyperpigmented scaly macules, mostly on trunk

•    More visible after sun exposure

•    Diagnosis: "spaghetti and meatballs" appearance on KOH prep

•    Treatment: topical selenium sulphide, azoles

Parasitic Infections

Scabies

•    Intense pruritus, worse at night

•    Burrows (fine, wavy lines) in interdigital spaces, wrists, umbilicus, groin

•    Nodules and excoriations common

•    Treatment:

o    Permethrin 5% cream (whole body, repeat in 7 days)

o    Treat close contacts simultaneously

Lice (Pediculosis)

•    Head lice: nits (eggs) attached to hair shafts

•    Body lice: live on clothing seams

•    Pubic lice: sexually transmitted

•    Treatment:

o    Topical permethrin or malathion

o    Mechanical removal (wet combing)

Mycobacterial and Tropical Infections

Cutaneous Tuberculosis

•    Lupus vulgaris: chronic reddish-brown plaques, "apple jelly" on diascopy

•    Scrofuloderma: skin breakdown over TB lymphadenitis

Leprosy (Hansen’s disease)

•    Hypopigmented or erythematous anaesthetic skin patches

•    Peripheral nerve thickening and sensory loss

•    Treatment: multidrug therapy (rifampicin, dapsone, clofazimine)

Leishmaniasis

•    Cutaneous leishmaniasis: ulcerating skin lesions, may heal with scarring

•    Visceral leishmaniasis (kala-azar): systemic; hepatosplenomegaly, pancytopenia

•    Diagnosis: amastigotes in skin biopsy or aspirates

Extra Revision Pearls

•    Painful vesicles: think HSV or VZV

•    Pruritus out of proportion to rash: think scabies

•    "Herald patch" vs "umbilicated papules": helps distinguish pityriasis rosea from molluscum

•    Diabetes and immunosuppression: predispose to fungal and deep bacterial infections