AN ITCHY RASH
History
Diamond is a 3-year-old boy who presents to his GP with an itchy rash that he has had for 4 days. He is otherwise well. He had bronchiolitis at the age of 4 months but has had no other diseases. He is not on any medication. His 5-year-old brother has eczema and his father has hay fever. He attends nursery three times a week. The family live in a onebedroom flat which is damp. His father smokes 20 cigarettes a da
Examination
He is systemically well and apyrexial. He is very itchy, cannot stop scratching and has obvious linear scratch marks. He has papules, pustules with some associated crusting and a few vesicles. The fingers, hands, flexor surfaces of the arms, axilla and feet seem to be the worst affected areas but there are also lesions around the umbilicus and on the face.
Questions
• What is the most likely diagnosis?
• What is the differential diagnosis of an itchy rash in a child?
• What is the treatment?
The most likely diagnosis is scabies. This is caused by the mite Sarcoptes scabiei and is highly contagious. Intense itching is typical. However, in children under 1 year this may present as irritability. A history of contact may be present. The classic features are burrows, papules, vesicles and pustules. Thread-like, linear burrows, typically in the finger webs and wrists, are pathognomonic but are often difficult to see. Definitive diagnosis involves removal of the mite from the burrow and examination under the microscope, but this, too, is difficult. Secondary bacterial infection due to scratching is common. In infants, the rash usually affects the palms, soles, axilla and scalp. In older children, lesions typically involve the web space between the fingers, the flexor aspects of the wrist and arm, the axilla and the waistline. The face is rarely involved in those over 5 years of age. Other areas of the body can also be affected. Although there is a strong family history of atopy, the patient has never had eczema and it would be unusual for eczema to present for the first time at this age in this way.
Common causes of an itchy rash in a child are:
• eczema – very common, often involves face, elbow and knee flexures
• seborrhoeic dermatitis – affects infants, often in association with cradle cap • scabies – itchy where mite has burrowed
• insect bites – affects uncovered areas such as arms and legs
• drug allergy
• urticaria – idiopathic or secondary to allergens, consists of wheal (raised and white) and flare (red)
• fungal infections – e.g. tinea capitis or tinea pedis (athlete’s foot)
• chickenpox.
Treatment consists of the application of scabicidal medication, e.g. permethrin. Family members and ‘kissing contacts’ should also be treated. Topical or oral antibiotics may also be required to treat secondary bacterial infection. Oral antihistamines and topical steroids, e.g. 1 per cent hydrocortisone, may be needed to help treat the itching. All clothing and bed linen should be laundered to remove eggs and mites. It can take 4–6 weeks for the itching to resolve. If lesions are still present at this time, persistent infection or reinfection should be suspected and treatment may need repeating.
KEY POINTS
• Scabies infestation causes severe itching.
• The classic features are linear burrows, papules, vesicles and pustules.
• The treatment of choice is permethrin.
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