What is this pustular lesion?

Pustular dermatosis

Dr. Emmanuelle Bourrat

Saint-Louis Hospital

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

Clinical case presentation

A 17-year-old young woman was in remission from cutaneous and renal lupus that had been evolving since the age of 13, treated with mycophenolate mofetil, hydroxychloroquine and enalapril. She also has a history of atopic dermatitis in childhood and acne during adolescence. She presented with an inflammatory dermatosis that had begun on the scalp, consisting of papules that subsequently became crusted and then alopecic.

In this context of iatrogenic immunosuppression, a mycological sample was taken and came back negative, ruling out tinea capitis. She was treated unsuccessfully with two courses of broad-spectrum antibiotic therapy and class III topical corticosteroids.

Subsequently, a diffuse dermatosis appeared in the form of well-demarcated annular plaques with a micropustular border on the trunk and limbs, as well as non-follicular macropustules in the axillary folds.

Complement levels were not decreased and lupus serology was stable, as was the renal workup. Histological examination of a skin biopsy showed multilocular intraepidermal pustules containing neutrophilic polymorphonuclear cells and a polymorphic dermal inflammatory infiltrate.

Your turn

What is your diagnosis?

Select 1 answer(s) from the following choices:

Pustular psoriasis

Folliculitis due to Pseudomonas aeruginosa

Amicrobial pustulosis of the folds

Flare of subacute cutaneous lupus erythematosus

Wrong answer!

Good answer!

Final diagnosis

This dermatosis meets all the necessary and sufficient Marzano diagnostic criteria for amicrobial pustulosis of the folds, namely:

An aseptic neutrophilic intraepidermal pustulosis of the major folds and scalp
Occurring in a young woman with at least one autoimmune disease (in this case, lupus).

The lack of lupus activity at the time of onset of this pustulosis confirms that the dermatosis and the autoimmune disease developed completely independently of each other.

Wrong answers explanations

Pustular psoriasis is a plausible clinicopathological diagnosis, but the context (lupus) suggests a more appropriate diagnosis.
Pseudomonas aeruginosa folliculitis is a bacterial infectious folliculitis that presents as inflammatory follicular pustules, often widespread and painful, occurring after bathing in warm stagnant water such as a jacuzzi. A bacteriological sample quickly confirms the diagnosis.
Subacute cutaneous lupus manifests as plaques, often annular or polycyclic, with centrifugal spread, but the elementary lesion is erythematosquamous, not pustular.

Treatment

The standard treatment for amicrobial pustulosis of the folds is systemic corticosteroid therapy at 0.5 mg/kg/day, a treatment the young patient refused. Dapsone was unsuccessful, as were six courses of anifrolumab. Treatment with an anti–IL-12/IL-23 agent has just been started by analogy with pustular psoriasis.

Expert's message

Amicrobial pustulosis is one of the neutrophilic dermatoses described in the context of systemic lupus erythematosus, but its clinical course is independent of that of lupus.

References:

^{Lagrange S, Chosidow O, Piette JC, Wechsler B, Godeau P,}
^{Frances C. A peculiar form of amicrobial pustulosis of the folds}
^{associated with systemic lupus erythematosus and other autoimmune diseases. Lupus 1997;6:514–20}