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History

This 9 year old boy is brought in by his mother with a 2 month history of red spots and blisters on his face. They occur only on his cheeks and they are sometimes itchy and painful. Individual lesions heal with pockmark like scarring. The child is otherwise well with no systemic symptoms and no other medical problems. His father had severe acne as a teenager.

CLUE 1: Note the patients young age and the absence of comedones (black and white heads)

CLUE 2: This eruption occurs particularly in summer and on sun exposed areas only What is your diagnosis:

1. Hydroa vacciniforme Yes This condition is a rare, sunlight-induced, intermittent, scarring eruption that affects sun-exposed skin, particularly the face and hands. It has the following characteristics; ? Onset usually begins in childhood, more often in males. It typically resolves by adolescence or early adulthood. ? The cause of the condition is unknown with only rare familial association. ? The eruption typically occurs in summer within hours of sun exposure and consists of symmetrical itching or burning macules, often with swelling. These progress over 24 hours to become tender papules, which vesiculate and may become confluent or haemorrhagic. Lesions heal over weeks after crusting over leaving varioliform (pocklike) scars. ? Typically there are no associated systemic symptoms, though fever and malaise can occur. ? Histological appearances are characteristic with focal intraepidermal vesiculation with reticular keratinocyte degeneration and as the lesions progress, confluent epidermal necrosis. Vesicles are filled with fibrin and acute inflammatory cells. There is also a superficial and deep perivascular infiltrate of lymphocytes, neutrophils and occasional eosinophils. immunofluorescence is non-specific and in severe cases a lobular or septal panniculitis may be present. ? UVA and UVB can both provoke this condition and this can be confirmed by phototesting. ? Other light-induced vesicular and scarring disorders must be excluded so viral studies, blood, urine and stool porphyrin levels, urinary amino-acid levels and serum ANAs and ENAs must be negative. ? Management of hydroa vacciniforme involves restriction of UVR exposure by appropriate protective clothing, broad-spectrum 30+ sunscreen and seeking shade between 11 and 3. In resistant cases, prophylactic, low-dose narrow band UVB or PUVA given several weeks before expected solar exposure can be effective (2-3 times weekly). Antimalarials (hydroxychloroquine) may be of benefit and rarely courses of immunosuppressive therapy including oral steroids have been used.

2. Polymorphous light eruption No This condition is predominantly seen in young women (usually late teens and early twenties) and though it causes a sun-induced symmetrical itchy papular rash, this is non-scarring and resolves within days. The correct diagnosis has been postulated to be a severe form of PLE because of the clinical and wavelength inducing (UVA and UVB) similarities.

3. Discoid lupus erythematosis No This autoimmune condition can occur in childhood and the face is most commonly affected by well-defined erythematous patches which may be bilateral and exacerbated by sunlight. Atrophic scars with healing can also occur. However the lesions of DLE tend to be more scaley with horny plugs rather than vesicles. A negative ANA and ENA and biopsy of the lesions will further exclude DLE and lend support for another diagnosis.

4. Acne vulgaris No This inflammatory condition is seen only after puberty and consists of comedones, pustules and papules. Therefore another diagnosis is more likely.

5. Erythropoietic protoporphyria No This deficiency in ferrochelatase leads to accumulation of protoporphyrins which are photosensitising. It thus typically presents in childhood in summer with oedematous urticaria-like plaques and eczematous areas on sunexposed sites which can lead to scarring. It is diagnosed by elevated blood protoporphyrin levels. However another diagnosis is more likely on clinical features .