Dermatology clinic
This month Susannah Baron discusses some skin infections and infestations that she has treated recently
Some people think that "skin disease is all about smelly scabs and scuzzy rashes.'' It is not all about that, but a large part of the dermatologist's workload does consist of treating cutaneous infections and infestations. These can be quite difficult to diagnose in the community so they often go untreated or are inappropriately treated for long periods of time. So I am going to discuss some of the patients whom I have treated recently.
Cutaneous infections
Bacterial infections
Children often present with impetigo. This superficial infection, usually caused by staphylococci or streptococci, has a characteristic honey coloured crust and is usually found on the face and hands. Children spread it among themselves quickly so it is important to treat early with topical antibiotics but in severe cases systemic antibiotics are required.
Cellulitis and erysipelas are two common acute soft tissue infections characterised by cutaneous erythema, warmth, oedema, and pain usually associated with a fever and a raised leucocytosis. They are both usually caused by streptococci (predominantly group A ß haemolytic). Erysipelas is a more superficial infection than cellulitis and commonly affects the face. In erysipelas the edge of the lesion is well demarcated and raised, whereas in cellulitis the edge is more diffuse.
This woman had a two day history of feeling systemically unwell and then noticed that her eye was beginning to swell. She presented with a pyrexia of 39.2 and rigors.
Question
- How would you manage this patient?
Answer
This patient needs to be admitted to hospital. Routine investigations would include a full blood count, CRP, blood cultures, and skin swab. Bacteria are present in affected tissue in small numbers and are difficult to culture. Therefore intravenous antibiotics should cover both streptococci and staphylococci--for example, benzylpenicillin and flucloxacillin. It is important to ask the opthalmologists to review the patient as sight can be threatened by severe infections. Orbital cellulitis (infection in the deeper orbital tissues) can be complicated by cavernous sinus thrombosis, cerebral abscesses, and meningitis. It is important to ask about predisposing factors in patients who have cellulitis, such as a history of trauma, chronic leg oedema, varicose eczema, interdigital fungal, bacterial infection, or diabetes mellitus. Patients who have recurrent cellulitis will often benefit from remaining on a prophylactic low dose of oral penicillin V.
Fungal infections
The superficial mycoses are the commonest of human fungal infections and they include dermatophytosis (ringworm) and infections with yeasts such as candida and pityrosporum.
The classical lesion of a dermatophyte infection is the ringworm. This is a round lesion whose rim is more inflamed and scaly than the centre. Typically this form occurs in infection of the body, tinea corporis. Dermatophyte infections are normally called "tinea" followed by the appropriate part of the body involved (in Latin of course)--for example, tinea pedis, tinea cruris, tinea capitis. Tinea incognito describes an atypical dermatophyte infection usually as the result of inappropriate use of topical steroids. It is important to take skin scrapings for microscopy and culture before beginning treatment with oral or topical antifungals.
This 45 year old woman presented with a 10 month history of a rash on her lower leg. It had originally been extremely itchy and had been treated for some months with topical steroid. Now it felt more painful and was spreading.
You can see that this is tinea corporis. The lesion is annular and has a distinct edge. The skin scrapings culture grew Trichophyton rubrum and the lesion cleared after a two week course of oral terbinafine.
Cutaneous infestations
This 26 year old woman comes to see you with a seven week history of a rash which is worse on her hands. It is extremely itchy, particularly at night, and she is worried in case it is infectious.
Questions
- What is the diagnosis?
- What other questions would you ask?
- What is the treatment?
Answers
This patient has scabies. In this case it has classically affected the finger webs and the sides of the fingers. Scratching has caused secondary bacterial infection. You should examine the patient fully paying particular attention to the toe webs, the flexor aspects of the wrists, the areolae of the nipples, and the penile or scrotal skin in men where scabetic nodules are often seen.
Scabies is caused by infestation with the mite Sarcoptes scabei. The female inhabits a burrow in the stratum corneum and eventually dies after laying her eggs. These then hatch and mature in 14 days and the cycle repeats itself. The itch is caused by a local hypersensitivity reaction.
It is important to ask about close contacts at home as these are probably infested even if they are not itching yet. It is also vital to ask about the patient's work. For example, if the patient worked in a nursing home or a hospital the staff and patients would need to be checked. Nursing homes can have large outbreaks of scabies and it is important to treat promptly if necessary.
The treatment is with topical preparations--for example, malathion and lyclear. It is important to treat all close contacts on the same day and the whole body from the neck to the soles of the feet must be treated. It is essential to reapply the solution after hand washing during the 24 hour period. After this time the solution is washed off and all clothing and bed linen washed. Patients often continue to itch for a few days after treatment. It is helpful to give written instructions to the patient as the commonest cause of persistent scabies infestation is inadequate application or reinfestation from contacts.
This 9 year old girl (above) has a 10 month history of an itchy scaly scalp. For the past six weeks she has been unable to wash or comb her hair and it is matted to the scalp. She has tried a variety of shampoos and lotions to no effect.
Questions
- What is the diagnosis?
- What is your differential diagnosis?
- What is your treatment?
Answers
This girl has pediculosis capitis, which is infestation with head lice. The term "nit" refers to the head louse egg, which is stuck to the hair shaft by its capsule. The symptoms occur when the louse hatches and causes an irritant dermatitis and scratching leads to secondary bacterial infection as can be seen here with the thick yellow crusts.
It is important to exclude an additional fungal infection by taking skin scrapings and hair pulls for microscopy and culture.
Unfortunately, we had to cut this girl's hair as it was too matted and uncomfortable to treat. Once cut we treated the hair and scalp with permethrin which was left on for 24 hours. The secondary bacterial infection was treated with a topical antibiotic preparation. The girl's mother was then encouraged to use a fine comb to comb out the dead nits. As with scabies, all contacts were examined and both the mother and the patient's sister were affected and treated. Treatment may need to be repeated after seven to 10 days but often children become reinfested from contacts at school. Unfortunately, the days of the "nit nurse" at school are over.
This 29 year old man (picture below) presented with a seven week history of an itchy lump on his inner thigh. He reported that the rash was changing and he could see a serpiginous track under the skin. On further questioning he reported that three months before he had been on holiday in Mexico and had spent much time on the beach.
Questions
- What is the diagnosis?
- What is the treatment?
Answers
This is cutaneous larva migrans which is a distinctive eruption with numerous causes. The lesions migrate because of the presence of moving parasites in the skin. Cutaneous larva migrans is usually caused by animal hookworms most commonly dog hookworm. Adult hookworms live in dog and cat intestines and their ova are deposited in the animals' faeces. Hot and humid climates are particularly favourable for hatching into infective larvae and these can be easily picked up on warm, sandy beaches. The larvae may cause a non-specific irritant dermatitis at the site of contact. The larvae can then lie quiet for weeks or months or immediately begin creeping under the skin. The larvae advance at a rate of a few millimetres to centimetres a day. Scratching can cause secondary changes of dermatitis or bacterial infection.
The disease is self limiting as the larvae tend to die within a few months. But most patients prefer treatment. Thiabendazole can be given either orally for three days or made up into a topical application.
Susannah Baron, specialist registrar in dermatology, Leeds
Email: zannerzu@aol.com
studentBMJ 2001;09:305-356 September ISSN 0966-6494
