"Infective Dermatoses" — Practice

Question 1

Which feature best distinguishes erysipelas from cellulitis?

Accepted Answer

A

Question 2

In suspected tinea corporis, skin scrapings should be taken from

Accepted Answer

B

Question 3

A 40-year-old has a rapidly spreading painful leg over 12 hours. The skin is only mildly erythematous but he is in severe pain with a heart rate of 128. What is the concern and the priority?

Accepted Answer

Necrotising fasciitis. Pain out of proportion to the visible findings is the hallmark and earliest sign, and the skin looks deceptively unimpressive because the infection tracks along fascial planes beneath it.

The priority is urgent surgical exploration with radical debridement, alongside broad-spectrum antibiotics and resuscitation. The LRINEC score may support the diagnosis but a low score does not exclude it and must never delay surgery. Antibiotics alone fail because necrotic fascia has no blood supply to deliver them.

Question 4

A family of five presents with itch worst at night. The father has finger web burrows and the 2-year-old has palm and sole lesions. Two members are asymptomatic. How do you treat them?

Accepted Answer

Treat all five simultaneously. Permethrin 5 per cent is applied to the whole body from the neck down in the adults and older children, and additionally to the scalp and face in the 2-year-old, since infants characteristically have palmar, plantar and scalp involvement. It is left on overnight and repeated after one week.

The asymptomatic members are treated regardless, because itch begins only four to six weeks after a first infestation once sensitisation has developed, so they may be infested but not yet symptomatic. Launder clothing and bedding hot or sun-dry it, and warn the family that itch may persist for several weeks after successful treatment as an allergic phenomenon rather than as treatment failure.

Question 5

A 55-year-old man has a red macerated rash in the groin extending onto the scrotum, with small pustules beyond its edge. What is the diagnosis and what should be checked?

Accepted Answer

Candidal intertrigo. Two features separate it decisively from tinea cruris: scrotal involvement, which tinea characteristically spares, and satellite pustules scattered beyond the main area, which dermatophytes do not produce. The rash is beefy red and macerated with a ragged edge rather than annular with central clearing.

What should be checked is his glucose. Candidal infection reflects a change in the local environment, and cutaneous or mucosal candidiasis in an adult without an obvious cause such as antibiotics or inhaled steroids is a recognised presentation of undiagnosed diabetes.

Question 6

A 32-year-old has extensive itchy annular lesions for eight months, treated repeatedly with a pharmacy combination cream. The lesions are now ill-defined and lack a raised edge. Explain and manage.

Accepted Answer

This is chronic recurrent dermatophytosis modified by topical corticosteroid, that is tinea incognito. The over-the-counter combination cream contains a potent steroid, which suppresses the inflammatory response responsible for the raised scaly border and the annular shape, so the lesion stops looking like ringworm while the fungus continues to spread.

Management begins with stopping the combination cream and confirming the diagnosis with a potassium hydroxide mount taken from the active edge.

Systemic treatment is required given the extent and chronicity, and in current Indian practice itraconazole at adequate dose and duration is the practical first-line agent, because Trichophyton indotineae carrying squalene epoxidase mutations makes terbinafine resistance common, reported around 70 per cent of isolates in published series. Treat household members, launder and sun-dry clothing and bedding, and counsel explicitly against returning to steroid-containing creams.

Question 7

A 28-year-old has a hypopigmented patch on the cheek. List the diagnoses to separate and how you would separate them.

Accepted Answer

The Indian differential includes leprosy, pityriasis versicolor, post-kala-azar dermal leishmaniasis, pityriasis alba and vitiligo.

Sensation separates leprosy. Definite loss of sensation within the patch is one of the three cardinal signs and should be tested with the eyes closed, comparing against adjacent normal skin, alongside palpation of peripheral nerves for thickening.

Scale separates pityriasis versicolor, which shows fine scale on stretching the skin and gives the spaghetti and meatballs appearance of short hyphae with spores on potassium hydroxide mount.

Pigment separates vitiligo, which is depigmented rather than hypopigmented and appears chalk-white with accentuation under Wood light.

Post-kala-azar dermal leishmaniasis requires a history of treated visceral leishmaniasis months to years earlier and matters because these patients form a reservoir sustaining transmission. Pityriasis alba is a diagnosis of exclusion in a child with an atopic tendency.

Question 8

A 62-year-old has had four episodes of cellulitis in the same leg in two years, each responding to antibiotics. Explain the pattern and outline what would actually reduce recurrence.

Accepted Answer

The recurrence is mechanical rather than microbial. Each episode of cellulitis damages dermal lymphatics, which impairs drainage and produces persistent oedema. Oedematous tissue has impaired local immune surveillance and a stretched, fragile epidermal barrier, so the next infection is more likely, and each episode worsens the lymphatic damage further. The cycle is self-reinforcing and eventually produces the thickened, cobblestoned skin of chronic lymphoedema.

What reduces recurrence is addressing the two ends of the cycle rather than changing antibiotic. First, find and treat the portal of entry, most often interdigital tinea pedis, fissured heels or venous eczema, since these are how organisms enter and they are easily overlooked. Second, treat the oedema with compression and elevation, and manage venous insufficiency if present.

Prophylactic penicillin is considered where episodes remain frequent despite these measures, but it is an adjunct to them rather than a substitute.

Question 9

A 26-year-old presents with herpes zoster affecting two adjacent thoracic dermatomes. He is otherwise well with no known illness. What should be done and why?

Accepted Answer

He should be offered HIV testing, alongside prompt antiviral treatment. Herpes zoster results from reactivation of latent varicella zoster virus in a dorsal root ganglion, and reactivation is normally a phenomenon of declining cell-mediated immunity with age or with recognised immunosuppression. Zoster in a young adult without an obvious cause is therefore a common disease behaving abnormally, and that abnormality is the signal.

Multidermatomal involvement strengthens the concern further, since disease crossing more than one dermatome suggests a less contained immune response.

The same reasoning applies to several other presentations in this chapter: extensive facial molluscum contagiosum in an adult, oral candidiasis without antibiotics or inhaled steroids, and crusted scabies. Each is an ordinary infection whose extent or behaviour implies impaired cell-mediated immunity, and each warrants consideration of HIV infection or, where relevant, undiagnosed diabetes.

Practice — "Infective Dermatoses"

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