ABSTRACT
A 4-year-old girl presented with a slowly expanding rash on her right cheek (Image 54a). The rash has been in the same location for weeks. The central older part of the lesion was grey-brown in colour with a raised itchy rim. This was presumed to be tinea facei and was treated with topical anti-fungal creams with little effect. Several physicians considered this a thermal burn and possible child abuse. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429170423/e1d751c1-a9c7-4bb9-9d59-53742c84031a/content/fig54a.jpg"/>
What is the diagnosis?
Name two ways to make a definitive diagnosis.
124Further history obtained from her mother notes the rash first appeared after the child was started on oral isoniazid for tuberculosis exposure. This is a fixed drug eruption as a result of treatment with isoniazid. Cutaneous drug eruptions are the most common adverse reactions attributed to drugs with the most common being fixed drug eruption. 1 Fixed drug eruption is a specific adverse reaction to medications that appears usually as a single or a few localized, sharply demarcated, round-to-oval, oedematous, dusky red macules or patches. 2 Lesions might appear locally as bullae or erosions. Rarely, some patients might have a severe clinical manifestation, such as extensive bullous eruptions.
There are two ways to make the diagnosis: one would be a skin biopsy; another would be to stop the medication, isoniazid in this case and closely follow up the rash. These types of drug hypersensitivity reactions are unique. The offending agent can be ingested, inhaled or given via suppository. The lesions develop within 2 weeks after exposure. Subsequent exposure leads to a rash within a day. The unique feature of this rash is that it always appears in the same location, occasionally with new spots elsewhere. The eruption can be anywhere on the body, head to toe, but tends to favour the ‘lips and tips’ meaning face, lips, hands, feet and genitals. As the initial erythema resolves a ‘gun metal gray’ colour remains. The erythematous oedematous variant has very large plaques (over 10 cm) as seen in this photo. They do not leave scars. Offending agents are often NSAIDS, antihistamines, paracetamol, tetrahydrozoline eyedrops, sulphonamides, barbituates, tetracyclines, carbamazepine and various laxatives. Skin biopsy is the definitive diagnostic procedure. Another example of such a rash is shown (Image 54b). If one stops administering the causative drug the rash will slowly fade over several weeks as the antigen is cleared from the skin. The centre can become darker in colour and remains for many months. Treatment is to identify the offending agent – remembering the over-the-counter ‘innocent’ items like vitamins, antihistamines. Topical steroid creams help with the itch and inflammation.
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