Acrodermatitis continuaFrom the Ronald O. Perelman Department of Dermatology, New York University
Benjamin E Rosenberg MD, and Bruce E Strober MD PhD
Dermatology Online Journal 10 (3): 9
A 54-year-old woman presented with a 5-year history of erythema and pustules on the distal portion of her left index finger. Acrodermatitis continua of Hallopeau is a rare, chronic, sterile pustular eruption affecting the distal aspects of the digits. It is often considered to be a variant of pustular psoriasis that tends to be resistant to both topical and systemic treatments for psoriasis.
History.—In June 2004, a 54-year-old woman presented to the New York University Dermatology Associates with a 5-year history of erythema and pustules on her left index finger. This condition, which was asymptomatic, was resistant to treatment with topical antifungal agents. She began treatment with acitretin 25 mg but chose to discontinue the medication because it induced alopecia. She was not interested in phototherapy and is currently applying clobetasol 0.1% ointment under occlusion with a good response. There was no personal or family history of psoriasis, and she denied any other medical problems.
Physical Examination.— Multiple pustules with erythema were present between the proximal nail fold and the distal interphalangeal joint on the left index finger. The fingernail on this digit was normal. No other lesions were noted on the patient's skin.
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Laboratory Data.— A bacterial culture of the pustules grew normal saprophytic flora that included the Streptococcus viridans group, Enterococcus species, and Diphtheroids. A fungal culture produced no growth.
Histopathology.— The stratum corneum shows compact parakeratosis and focal aggregates of neutrophils. Only a superficial portion of epidermis is identified and is histologically unremarkable. A periodic-acid-Schiff stain was negative for fungal hyphae.
Acrodermatitis continua of Hallopeau, which was also known as dermatitis repens, is a rare, chronic, localized, sterile pustular eruption of the fingers and toes.  Although it is generally considered to be a variant of pustular psoriasis, some individuals classify it as a separate entity.  It is most common in middle-aged women and often begins after localized trauma or infection on a single digit. 
Acrodermatitis continua, which is characterized by multiple pustules with scale on an erythematous base, is usually restricted to a distal location on one or two digits. The pustules may coalesce to form lakes of pus, and, over time, they may spread proximally to involve the dorsal aspects of the hands, forearms, and feet. Pustulation of the nail bed and nail matrix often is associated with onychodystrophy and even anonychia of the involved digits. Over time, some patients will develop osteolysis of the distal phalanx that underlies the eruption. 
Histologically, acrodermatitis continua displays features of pustular psoriasis that include subcorneal neutrophilic pustules.  This disorder is easily misdiagnosed as bacterial or fungal paronychia, owing to its chronic purulent discharge; other entities in the differential diagnosis include allergic contact dermatitis and dyshidrotic eczema.
Acrodermatitis continua can be resistant to treatment. It may be treated topically with glucocorticoids, calcipotriene, or 5-fluorouracil. Systemic treatments include oral retinoids, cyclosporine, methotrexate, and PUVA photochemotherapy. [1-3]
References1. Yerushalmi J, et al. Chronic pustular eruption of the thumbs. Arch Dermatol 2000; 136:925.
2. Gluckman SJ, Heyman, W. Diagnosis: acrodermatitis continua of Hallopeau. Clin Infect Dis 2001; 32:505.
3. Mozzanica, N, Cattaneo, A. The clinical effect of topical calcipotriol in acrodermatitis continua of Hallopeau. Br J Dermatol 1998; 138:556.
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