Treatment of Refractory Pityriasis Rubra Pilaris With Novel Phosphodiesterase 4 (PDE4) Inhibitor Apremilast

Discussion | Acrodermatitis continua of Hallopeau, also known as acrodermatitis perstans and dermatitis repens, is a rare inflammatory pustular dermatosis of the distal fingers and toes. It is considered a variant of pustular psoriasis or, less commonly, its own pustular psoriasis-like independent entity.1 Precise pathophysiology and incidence are unknown. Case literature suggests predominance in women, but the disease affects both sexes and, rarely, children.2 Acrodermatitis continua of Hallopeau initially presents as erythema overlying the distal digits that evolves into pustules.2 The nail bed is often involved, with paronychial and subungual involvement and atrophic skin changes.3 Most patients experience a chronic, relapsing course involving the proximal digit as the condition worsens.4 Acrodermatitis continua of Hallopeau has been reported to both evolve into and stem from generalized plaque or pustular psoriasis.3 The present patient was noted to have plaque psoriasis lesions nearly 1 year after the onset of her disease. Psoriatic arthritis is a rare complication,3 but distal phalanx osteolysis is an important comorbidity.1 The differential diagnosis includes infectious paronychia of viral, fungal, or bacterial etiology, infected contact dermatitis, and dyshidrotic eczema.4 Gram stain, potassium hydroxide mount, culture, and microscopy may be useful in diagnosis. Histopathologically, ACH is characterized by neutrophil-rich spongiform pustules within the epidermis, dermal edema, and lymphohistiocytosis.4 As in pustular psoriasis, biopsy from the nail bed often reveals acanthosis and spongiform pustules.3 Treatment with topical corticosteroids, tacrolimus, fluorouracil, calcipotriol, methotrexate, acitretin, cyclosporine, and phototherapy have produced inconsistent responses. Successful treatment with tumor necrosis factor inhibitors and the IL-1 inhibitor anakinra5 have been reported. However, these agents are not always efficacious and may even have the potential to incite pustular psoriasis.6 Two cases of ACH treated with concomitant ustekinumab and acitretin have been reported, one successfully,1 the other unsuccessfully.5 The present case is the first to our knowledge to be successfully treated with ustekinumab as monotherapy. Given that the literature supports ustekinumab as monotherapy and concomitant therapy for pustular psoriasis, ustekinumab was a reasonable choice for our patient and succeeded when other agents had failed.