Pustules of the fingers: acrodermatitis continua

A woman in her fifties presented with pustules on her right thumb and left index finger (Figure 1). She reported picking the affected skin, which subsequently worsened the condition over one year. There was no personal or family history of psoriasis. Her condition improved with topical clobetasol propionate, calcipotriol and avoidance of trauma. Her hands worsened several months later, and plaque-type psoriasis developed on her body, requiring methotrexate (15 mg/wk). After several months of treatment with methotrexate, she stopped the medication because of adverse effects and minimal response. She was not interested in pursuing any further systemic treatment at the time.

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Figure 1:

(A) Right thumb of a woman in her fifties showing well-defined, erythematous, scaly plaque over the palmar aspect of the distal phalanx. Note the remnant of pustules in the centre of the plaque. (B) The patient’s left index finger showing anonychia with well-defined erythema, edema and crusting of the distal phalanx.

Acrodermatitis continua (of Hallopeau) is a rare variant of pustular psoriasis. Disease incidence is difficult to estimate given the rarity of the disease, with about 100 case reports.1 The condition presents with sterile acral pustules, often restricted to one or two digits of the hands and feet. Nail-bed and matrix involvement may lead to onychodystrophy, anonychia and osteolysis.2 Acrodermatitis continua has a relapsing course and may be refractory to standard psoriasis therapies such as steroids, calcipotriol, phototherapy, acitretin and immunosuppressants (e.g., methotrexate and cyclosporine). Recent literature describes successful treatment with newer biologic agents for refractory cases.1^–3 However, anti–tumour necrosis factor therapies have been found to cause pustular psoriasis and acrodermatitis continua.4 Aggressive treatment is warranted given the destructive tendency of the disease, potentially leading to resorptive osteolysis of digits.1^,2

Acrodermatitis continua is commonly misdiagnosed as bacterial, viral or fungal paronychia because of purulence and nail involvement. The differential diagnosis includes dyshidrotic eczema, contact dermatitis and squamous cell carcinoma.5 Histopathologic, Gram stain, KOH and culture testing to rule out infection and other causes of pustules can aid in the diagnosis. However, progression of the disease is often what leads to the diagnosis. Accurate diagnosis is imperative; early treatment of this condition is important to avoid its destructive and disabling effects.