Less weight, more pimples

Inflammatory dermatosis

Dr. Emmanuelle Bourrat

Saint-Louis Hospital

The clinical case
Now it's your turn!
Co-prescription and advice

Clinical case presentation

A 32-year-old man with no previous history of being overweight began a very restrictive diet with only one meal a day; he lost 12 kg in two months, i.e. 12% of his body weight, reducing his BMI from 23.6 kg/m² to 19.35 kg/m². He presented with a highly inflammatory but not very pruritic rash localized on the upper trunk (pre-thoracic region, upper back and nape of the neck). The rash consisted of seropapules with a slightly reticulated arrangement; the scalp was more discreetly affected.

Suspecting a possible allergy to a hair product, an open test was performed on the elbow crease for 5 days, which was negative. Questioning revealed no other contact factor, but given the possibility of contact eczema, treatment with a class IV topical corticosteroid was prescribed with no improvement.

Skin biopsy revealed a spongiotic, orthokeratotic epidermis with numerous keratinocyte necroses and intraepidermal vesicles containing lymphocytes, histiocytes and eosinophils. The superficial dermis was edematous, with an infiltrate rich in eosinophils and lymphocytes. PAS was negative, as were Alcian blue staining, anti-herpes immunohistochemistry and direct immunofluorescence.

Your turn

What's your diagnosis?

Select 1 answer(s) from the following choices:

Confluent and reticulated papillomatosis of Gougerot-Carteaud

Reticular erythematous mucinosis (REM syndrome)

Necrolytic migratory erythema associated with glucagonoma

Keto rash

Wrong answer!

Good answer!

Selected diagnosis

The histological appearance, combined with the context of a highly restrictive diet, suggests a “keto rash” or prurigo pigmentosa induced by a ketogenic diet.

Prurigo pigmentosa (PP) was first described in 1971 as plaques of inflammatory papules with a reticulated arrangement on the trunk, sometimes progressing to pigmented sequelae, often described in pregnant women. It was only in 2015 that the link between PP and the ketogenic diet was made, but there is still no satisfactory pathophysiological explanation for this association, of which several dozen cases have been published. The most consistently effective treatment is cessation of the diet; when the diet must be maintained, as it is indicated in certain severe childhood epilepsies, various topical or oral anti-inflammatory treatments (cyclines) may be proposed.

Explanation of wrong answers

The confluent and reticulated papillomatosis described by Gougerot and Carteaud is a dermatosis affecting the trunk in adolescents and young adults whose basic lesion clinically and histologically resembles acanthosis nigricans. It is therefore not an inflammatory dermatosis and its remarkable sensitivity to tetracyclines suggests an epidermal dysbiosis.
Reticular erythematous mucinosis is a persistent eruption in the form of erythematous papules and macules (not vesicles), confluent into patches or reticular in appearance, located in the mid-dorsal or mid-thoracic area. This very chronic dermatosis is sometimes associated with lupus. Diagnosis is histological (dermal mucinosis associated with a perivascular lymphocytic infiltrate).
Necrolytic migratory erythema secondary to a glucagonoma is an inflammatory dermatosis with maculopapular plaques of centrifugal evolution, with a vesiculoerosive and desquamative border. The lesions predominate in the folds or in the periorificial zone, often in a context of marked deterioration of general health.

Message from the expert

Keto rash is one of the dermatologic manifestations of eating disorders: it should be investigated in the context of a highly restrictive diet with a particular focus on carbohydrates.