Erythema and scaling of the finger and nail bed

Acrodermatitis continua of Hallopeau (ACH) is a recurrent inflammatory condition, usually of the distal finger. Although some clinicians classify ACH as a distinct entity, others believe the condition to be a variant of pustular psoriasis, as it has been observed...

Submit your diagnosis to see full explanation.

Acrodermatitis continua of Hallopeau (ACH) is a recurrent inflammatory condition, usually of the distal finger. Although some clinicians classify ACH as a distinct entity, others believe the condition to be a variant of pustular psoriasis, as it has been observed to occur in patients with palmoplantar or generalized pustular psoriasis. ACH may be more prevalent in middle-aged women; however, it can present at any age.^1,2 In a study of 1,262 patients with infantile psoriasis, 4.7% of patients were noted to have ACH.³

The pathogenesis of ACH is not known, but the condition often occurs after minor trauma or infection of the involved digit.¹ Recently, an autosomal recessively inherited mutation in the IL36RN gene, which encodes interleukin-36 receptor antagonist (IL-36Ra), was identified in a male patient with ACH and in his sister with generalized pustular psoriasis.⁴ This shared genetic mutation lends evidence to the belief that ACH is one manifestation of pustular psoriasis. Medications have also been implicated in ACH: An 81-year-old man developed ACH two weeks after starting oral terbinafine (Lamisil) for treatment of tinea pedis.⁵

ACH usually affects one digit, and its course is chronic and relapsing. The disease usually starts as a pustule in the nail bed or as paronychia. The patient may later develop an eruption of fresh pustules around and under the nail plate with hyperkeratosis and crusting.⁶ Patients may also variably complain of onycholysis, onychomadesis, and scaling of the nail bed and periungual skin.⁷ Onycholysis is defined as separation of the nail plate from the distal nail bed; onychomadesis refers to separation of the nail plate from the proximal nail bed. After many relapses, anonychia and/or tapering of the fingertips to long keratotic points may result.

A full-body skin exam should be performed and a dermatologic history should be obtained for evidence of concomitant palmoplantar or generalized pustular psoriasis. The most common locations for palmoplantar pustulosis are the thenar or hypothenar eminences or the central portion of the palms and soles. Early on, pustules will be visible. In later lesions, only denuded areas, crusts, or collarettes of scale may be visible where the pustules had been. Generalized pustular psoriasis typically presents with the sudden onset of lakes of pus most prominently in the flexures and at the edges of psoriatic plaques.

The diagnosis of ACH can easily be made when patients also present with palmoplantar pustulosis or generalized pustular psoriasis. The diagnosis can be challenging when only one digit is affected. A bacterial, fungal, and viral culture is often obtained to rule out infectious paronychia. A skin biopsy can confirm the diagnosis and rule out other etiologies. Histologically, intraepithelial spongiform pustules may be seen in the acute stage. This histopathologic finding is indistinguishable from pustular psoriasis. Older lesions may show hyperkeratosis with parakeratosis or atrophy.⁶

The differential diagnosis of ACH includes acute contact dermatitis, dyshidrotic hand eczema, acute paronychia, viral paronychia, and onychomycosis caused by non- dermatophyte molds. In acute contact dermatitis, the lesions are usually vesicular rather than pustular. There is usually a significant amount of surrounding erythema and edema with weeping, and the condition is not usually limited to the distal digit. A detailed history will often reveal exposure to an allergenic agent. A geometric appearance is highly suggestive of an exogenous exposure.

Dyshidrotic eczema is a chronic skin condition characterized by the recurrent onset of tense and deep-seated vesicles. The most common location of dyshidrotic eczema is the lateral fingers, followed by the palms and soles. Unlike allergic contact dermatitis and ACH, there is no surrounding erythema in cases of dyshidrotic eczema. These vesicles typically resolve without rupturing, so in later stages, only desquamation may be evident.

Acute paronychia may also present with a swollen, red, and painful distal digit and is usually limited to a single episode. Compression of the nail fold may produce purulent drainage. The most common causative bacteria are Staphylococcus aureus and Strepotococcus pyogenes. ACH can be distinguished from acute paronychia by a negative bacterial culture and chronic relapsing course.

Viral paronychia caused by herpes simplex virus is also known as herpetic whitlow. This condition presents with pain, swelling, and vesicular lesions of the digits. Recurrences are common. Although the nail plate can be affected during flares, the nail heals completely between episodes, unlike in ACH. A viral culture, direct fluorescent antibody test, or polymerase chain reaction can confirm the diagnosis of herpetic whitlow.

Finally, onychomycosis due to non-dermatophyte molds may also be confused with ACH. Onychomycosis attributable to molds presents with periungual or subungual inflammation and a purulent discharge. Unlike ACH, onychomycosis tends to be chronic and progressive, not chronic with flares. A fungal culture is required for diagnosis, but this can take weeks to months.

For mild disease, potent topical corticosteroids, vitamin D3 analogues (calcipotriene [Dovonex, Sorilux], calcitriol [Rocaltrol]), or tacrolimus 0.1% ointment (Protopic) alone or in combination may be initiated.8,⁹ Occlusion with plastic gloves at night may increase efficacy of topical therapies. Success with topical fluorouracil 5% cream (Carac, Efudex, Fluoroplex) has been reported; however, skin lesions recurred after discontinuing medication.¹⁰ For severe disease, systemic therapies may be necessary and should be managed by a dermatologist familiar with these medications. Acitretin (Soriatane) may be attempted, but it may be several weeks before improvement is noted. Phototherapy and systemic therapies commonly used for psoriasis have been used with success in the treatment of ACH. Improvement with methotrexate (Rheumatrex, Trexall), cyclosporine (Gengraf, Neoral, Sandimmune), tumor necrosis factor (TNF) inhibitors (etanercept [Enbrel], adalimumab [Humira], infliximab [Remicade]), and ustekinumab (Stelara) has been reported.¹¹ A case of acitretin- and TNF-inhibitor-resistant ACH responding to anakinra (Kineret), an interleukin-1 receptor antagonist, has been reported.¹²

Because of this patient’s history of cirrhosis, a contraindication for treatment with methotrexate and TNF inhibitors, he was started on cyclosporine. At his two-week follow-up visit, his skin had improved, but his creatinine had increased by more than 50%, and cyclosporine was discontinued. No further treatment was initiated because of the patient’s failing health related to his cirrhosis.

Audrey Chan is a third-year dermatology resident at Baylor College of Medicine in Houston.