15. Skin Infections

Question 1

Outline the aetiology pathophysiology of cellulitis + erysipelas

Answer 1

Ae = Group A streptococci (pyogenes), Staph aureus
- RF: insect/spider bite, blistering, animal bite, tattoos, pruritic skin rash, surgery, athletes’ foot, eczema, IV drugs

CELLULITIS =

• Infection affecting the lower dermis and subcut fat
• Typically lasts 7-10 days

ERYSIPELAS =
- acute superficial form of cellulitis - involves dermis and upper subcut tissue

Question 2

List the signs and symptoms of cellulitis

Answer 2

Erythema that increases in size - most common lower limb

Irregular borders (distinguished from erysipelas by well-defined red raised border)

Hot to touch

Swollen skin, blistering, erosion, ulcers, abscess, dimpling

Pain

General fever

Tiredness

Question 3

How should cellulitis be investigated?

Answer 3

Clinical Dx

Wound swab - C+S

US - rule out DVT

Question 4

How should cellulitis be managed?

Answer 4

Abx - cephalexin, amoxicillin, erythromycin

Analgesia

Surgical drainage of abscess

Sepsis 6 - if it has devel this far

Comp = abscess, nec fasciitis, sepsis, gas gangrene, endocarditis

Question 5

What are the causes and pathophysiology of impetigo?

Answer 5

Bacterial - staph aureus, strep pyogenes

Involves superficial layers of skin

Spread via direct skin-to-skin contact

Duration - < 3 weeks

Question 6

What are the signs and symptoms of impetigo?

Answer 6

Often begins as red sore near the nose or mouth, painful itchy yellowish crusts, lymphadenopathy

Question 7

How should impetigo be managed and what are its possible complications?

Answer 7

Abx - topical = mupirocin, fusidic acid, oral = cephalexin

Comp =

• Cellulitis
• Post-streptococcal glomerulonephritis

Question 8

Outline the aetiology + pathophysiology of folliculitis

Answer 8

Chronic infection of hair follicles, can also be damaged

Question 9

What are the signs and symptoms of folliculitis?

Answer 9

Small red bumps, white headed pimples, itchiness

Question 10

How should folliculitis be managed?

Answer 10

Topical antiseptic (tea tree oil), topical Abx (zineryt - topical erythromycin), fungal - fluconazole

Question 11

Outline Scabies

Answer 11

Scabies is an infestation of tiny mites that burrow into the epidermis of the skin

• may have Hx of contact
• pruritus worse at night

LINEAR burrows or rubbery nodules
<2y = rash on head, neck, palms, soles
>2 y = rash on hands, between fingers, wrists, belt line, thighs, naval, groin, chest, armpits

Mx = Permethrin 5% cream for 8-10h then wash off, antihistamine
- all linin, family members, friends and sexual contacts should be treated at the same time whether they are itchy or not

Question 12

Outline head lice

Answer 12

Tiny parasitic insects that can infest the skin

Spread from person to person by close body contact, and by shared clothes and other personal items

S+S = itching, visible eggs/nits

Mx = medicated cream rinse or shampoo, fine-tooth comb, checking family, washing all bedding and clothing in hot water

Question 13

What is the aetiology of varicella (chicken pox)?

Answer 13

Aetiology = varicella zoster virus (VZV)

Question 14

How does varicella present?

Answer 14

Small, erythematous macules appear on the scalp, face, trunk, and proximal limbs, which progress over 12–14h to papules, clear vesicles (which are intensely itchy), and pustules

Crusting occurs usually within 5d of the onset of the rash, and crusts fall off after 1–2w

Headache, loss of appetite, tiredness, fever

Onset = 10–21 days after exposure

Duration = 5–7 days

Question 15

Outline the management of a varicella infection

Answer 15

Topical calamine lotion - alleviate itch

Chlorphenamine - itch associated with chickenpox for people 1 year of age or older.

Paracetamol - if pain or fever are causing distress

Oral acyclovir - for those who presents within 24 hours of rash onset

Question 16

What is staph scaled skin syndrome, its presentation and a DDx?

Answer 16

Staph (coag +ve) produces an exfoliative toxin that causes the outer layers of skin to blister and peel, as if they’ve been doused with a hot liquid

Most common in children under 6

S+S = fever, irritability, widespread erythema, within 24-48h fluid-filled blisters form; rupture easily, leaving an area that looks like a burn, tissue paper-like wrinkling of the skin, Nikolsky sign (top layers of the skin slip away)

Mx = Abx, analgesia

DDx = drug hypersensitivity, viral exanthemas, scarlet fever, thermal burns, epidermolysis bullosa, toxic epidermal necrolysis

Question 17

Outline the aetiology and pathophysiology of syphilis

Answer 17

Ae = STI - spirochete Treponema pallidum

Path = transmission sexually/blood/vertically, symptomatic and asymptomatic stages, cutaneous lesions where T. pallidum uses its spiral shape to twist into the skin

Question 18

How does syphilis present?

Answer 18

Congenital = maculopapular rash, vesiculobullous lesions, mucous patches, condyloma lata, or as rhinitis (inflamed mucous membrane in the nose causing snuffles)

PRIMARY
- Solitary, small firm red painless papule on the genital area quickly becomes a painless ulcer with a well-defined margin and an indurated base

SEC

• Rash trunk, palms, soles (rough, red or reddish-brown papules or plaques)
• Greyish-white, moist plaques occur in the groin, inner thighs, armpits, umbilicus, or under the breasts; these are called condyloma lata
• Raw mucous surfaces

LATENT
- Asymptomatic

TERT (30-40y later)
- Gumma: solitary granulomatous lesion with central necrosis

Question 19

How should syphilis be Ix and Mx?

Answer 19

Ix = serology or dark-field microscopy or by treponemal polymerase chain reaction (PCR) testing

Mx = benzathine or procaine penicillin injection

Question 20

Outline herpes simples

Answer 20

Ae = HSV1 (oral), HSV2 (genital)

• often triggered by a febrile illness
• after the primary ep, HSV resides in latent state in spinal dorsal root nerves

S+S =

• HSV1: whitish vesicles evolve to yellowish ulcers on the tongue, throat, palate and inside the cheeks, LN, fever
• HSV2: painful vesicles, ulcers, redness and swelling, inguinal LN

Ix = culture, viral swab PCR

Mx = acyclovir

Comp = eczema herpeticum

Question 21

Outline syphilis

Answer 21

Ae/path = VZV remains dormant in dorsal root ganglia nerve cells in the spine for years before it is reactivated and migrates down sensory nerves to the skin to cause herpes zoster

S+S = blistering red papules, dermatomal distribution, can become pustular then crusting

Ix = clinical Dx

Mx = acyclovir started 1-3d within start of Sx, rest, pain relief, protective ointment, oral Abx (sec infection)

Question 22

What is molluscum contagiosum

Answer 22

Ae = poxvirus, via skin-to-skin, towels, scratching/shaving, sexual

S+S = localised clusters of epidermal papules, white, pink or brown, waxy, shiny look with a small central pit

Ix = clinic Dx

Mx = self-limiting, cryotherapy, curettage or electrodessication, laser ablation

***advice and guidance to not share towels, flannels or clothing, avoiding squeezing spots, avoiding sharing baths and keeping affected areas covered

Question 23

Outline the different tinea infections

Answer 23

Fungus in the horny layer of skin, hair, and nailbeds called dermatophytes

Types:

1) Tinea pedis (athletes foot): white, scaling, itchy, blisters (Tx: dry feet, topical AF)
2) Tinea cruris (Jock itch): red, ring-like patches in the groin area (Tx: systemic AF)
3) Tinea capitis (scalp): scaly, itchy, hair loss (Tx: systemic AF)
4) Tinea corporis (ringworm): trunk/limbs, circular scaly edge (Tx: topical AF)
5) Tinea unguium (nail): thickened, deformed, yellowing (Tx: topical AF)

Mx = antifungals 4-8w +/- shampoo, Tx pet if infected

Question 24

Outline Candidal intertrigo

Answer 24

Ae = superficial skin-fold infection caused by the yeast, candida
- triggered by combination: hot, damp, skin friction, immunosuppression

S+S = erythematous and macerated plaques with peripheral scaling, often associated superficial satellite papules or pustules

Ix = fungal microscopy and culture of skin swabs and scrapings

Mx =

• address RF: weight loss, blood glucose control and avoidance of tight clothing, cool and moisture-free skin
• clotrimazole cream

Question 25

Describe pityriasis versicolor

Answer 25

Ae/path = mycelial growth of fungi of the genus Malassezia (normal flora)

• white: chem impairs the function of the melanocytes
• pink: dermatiits

S+S = flaky discoloured patches appear on the chest and back, multiple colours (coppery brown, paler than surrounding skin, or pink), pale patches may be more common in darker skin (pityriasis versicolor alba),

Ix = clinical Dx

Mx = Topical azole cream/shampoo (econazole, ketoconazole)

Question 26

Discuss Tinae capitis

Answer 26

(scalp ringworm)

Ae = dermatophyte fungi (microsporum canis, trichophyton tonsurans)

Path =

• Ectothrix: confined to hair surface
• Endothrix: invades hair shaft and internalise into hair cell
• Favus: honeycomb destruction of hair shaft
• Most commonly healthy preadolescent children + immunocompromised adults

S+S = erythematous, scaling, patch of broken hair, regional LN

Ix =

• Woods lamp: dermophyte fungi are bright green fluorescent
• Dermoscopy: black dot hairs, comma shaped hairs, cork-screw hairs
• MC+S: scraping

Mx = systemic Tx: terbinafine, griseofulvin, topical Tx (reduce transmission of spores)

Question 27

Outline a DDx for chickenpox

Answer 27

Other vesicular viral rashes, such as:

• Herpes simplex (not usually disseminated)
• Herpes zoster (usually unilateral and localized to dermatomes)
• Hand, foot, and mouth disease (Coxsackie virus)

Question 28

Discuss paediatric ringworm

Answer 28

Fungus in the horny layer of skin, hair, and nailbeds called dermatophytes

Types:

• Athletes foot: white, scaling, itchy, blisters
• Jock itch: red, ring-like patches in the groin area
• Scalp: scaly, itchy, hair loss
• Nail: thickened, deformed, yellowing

Mx = antifungals 4-8w +/- shampoo, Tx pet if infected

Question 29

Outline measles

Answer 29

RUBEOLA VIRUS (paramyxovirus family) = airborne/droplet transmission

S+S = fever, cough, red eyes, koplik’s spots on mucous membranes, rash (maculopapular erythematous), white spots surrounded by red mucosa

Ix = IgM/G, viral RNA PCR

Mx = notifiable, rest, drink fluids, paracetamol/ibuprofen, MMR, stay off school (self-limiting)

Comp = otitis media, pneumonia, diarrhoea, convulsions

Question 30

Outline rubella

Answer 30

RUBELLA VIRUS

S+S = fever, conjunctivitis, tender, post-auricular LN, URTI, rash (transient red/pink maculopapular, starts of face then trunk then extremities)

Ix = IgM/G assays, viral PCR

Mx = notifiable, drink fluids, paracetamol/ibuprofen, stay off school, get up-to-date with vaccines (self-limiting)

Comp = congenital rubella syndrome in preg, encephalitis, thrombocytopenia

Question 31

Outline scarlet fever

Answer 31

S.PYOGENES, direct contact/resp droplets

S+S = red blanching punctate rash, feels like sandpaper, starts on trunk then spread to other parts rapidly, white coating on the tongue which peels away to give a strawberry tongue appearance, fever, sore throat, N+V, headache, lymphadenopathy

Ix = clinical Dx, (can be confirmed with throat swab)

Mx = penicillin V, paracetamol/ibuprofen, oral fluids, rest

Comp = tonsil abscesses, ear/sinus/skin infections, pneumonia, post-strep glomerulonephritis

Question 32

Outline hand, foot and mouth disease

Answer 32

Coxsackievirus A16

S+S = painful ulcerative oral lesions (hard palate, tongue, buccal mucosa), hands/feet: erythematous macules or papules with central grey vesicle, fever, loss of appetite, cough, abdo pain

Ix = clinical Dx

Mx = fluid intake, paracetamol/ibuprofen (self-limiting)

Comp = dehydration, viral meningitis , encephalitis

Question 33

Outline Roseola infantum

Answer 33

Herpes 6/7, children <3y (NOT NOTIFIABLE)

S+S = high fever for 3d, abdo pain, malaise, +/- URTI, eyelid oedema, rash: small pink macules +/- papules starting on the trunk/neck

Ix = clinical Dx

Mx = (self-limiting)

Comp = febrile seizures

Question 34

Outline erythema infectiosum (slapped cheeck)

Answer 34

Slapped cheek syndrome (5th disease) = parvovirus B19 via resp droplets

S+S = rash: biphasic erythematous and oedematous plaques on cheeks with nasal bridge and periorbital sparing, reticulate appearance as it fades away

Ix = clinical Dx

Mx = rest, drink fluids, paracetamol/ibuprofen

Comp = fetal hydrops, CHF, anaemia

Question 35

Outline erythema multiforme

Answer 35

Hypersensitivity reaction usually triggered by infections, most commonly herpes simplex virus (HSV)

Presents with a skin eruption characterised by a typical target lesion

It is acute and self-limiting, usually resolving without complications