Mrs A was worried that she had developed an allergy to sunlight.

She had been tanning on a sunbed and had developed white patches on her body.

On examination, there were multiple small circular patches of hypopigmentation over her trunk, arms and upper thighs, with a fine surface scale.

The patient had pityriasis versicolor, a superficial fungal infection caused by Pityrosporum ovale, a normal commensal present in hair follicles that can become pathogenic.

When the patient is untanned the lesions appear as pinky- brown, slightly scaly macules. The scale can be raised by gently scraping the skin with a scalpel. If the patient is tanned or has darker skin, the macules appear hypopigmented.

Diagnosis of pityriasis versicolor is usually made clinically. Skin scrapings can be examined microscopically, but it is not useful to send them for culture because the yeast is difficult to grow.

Pityriasis versicolor develops gradually, but will not disappear unless treated. If the disease is relatively limited, topical preparations, such as selenium lotion or shampoo, can be used. This is applied to the entire skin surface, from the posterior hairline to the thighs, and washed off after 10 minutes. The treatment is repeated daily for one week. Topical imidazole can be applied twice daily for two to four weeks.

Topical treatment is effective, but recurrence is high. For patients with extensive infection or recurrence, oral treatment with itraconazole 200mg for seven days will give cure rates of more than 90 per cent.

Patients should be warned that hypopigmentation will not go instantly, but sunlight encourages skin to repigment.

Unusual presentation

Mr B presented with an itchy and painful rash in his groin. He had been self-medicating with hydrocortisone and various other OTC creams.

On examination, he had an erythematous rash with surrounding excoriations.

There were a few pustules in the erythematous area and this was thought to be a sweat rash with secondary infection.

The patient was treated with betamethasone/fusidic acid cream and advised to contact the surgery if there was no improvement. Initially, he was pleased because the irritation and redness settled down and the pustules lessened. But just after stopping the cream he developed multiple painful pustules around the groin, perineum and buttocks.

The rash was thought to be a folliculitis because its predominant feature was the pustules, with little surrounding erythema. Mr B was given a course of flucloxacillin, which partially resolved the rash, but needed a further course of co-amoxiclav to resolve the pustules. He returned to the surgery within a week of completing his second course of antibiotics. As soon as they were finished, the pustules recurred.

Recurrent problem

On examination, he again had significant numbers of pustules over the groin, buttocks and perineum. At this stage, swabs were taken from his nose, throat, axillae and groin to assess for micro-organisms.

The pustules cleared with the antibiotics. The swabs showed colonisation with staphylococci, which was treated accordingly. Mr B later presented with another crop of pustules. He was distressed and the advice of a dermatologist was sought.

Skin scrapings taken at the hospital showed that this was a fungal infection, tinea incognito. Mr B was treated with topical antifungals, terbinafine and clotrimazole, and has had no recurrence since then.

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LESSONS LEARNT FROM THESE CASES

- Pityriasis versicolor develops gradually, but will not disappear unless treated.

- Fungal infections treated with corticosteroids can present the GP with a diagnostic problem.

- Corticosteroids will dampen the inflammatory aspect of the fungal infection, but allow the organism to grow.

- When a patient presents with an unusual rash, a history of what they have already applied can be very useful. If the patient has used corticosteroids, consider taking scrapings for fungal infection.