UPP - Department of Dermatology, Dermatopathology Unit
Jeffrey Shackelton, MD, Jonhan Ho, MD, Timothy Patton, DO
JUNE 2011 WEB CASE OF THE MONTH
Erythema dyschromicum perstans
Discussion
Erythema dyschromicum perstans (EDP) was first described by Ramirez in El Salvador in 1957.1 It is an asymptomatic, chronic, slowly progressive cutaneous eruption that most common affects dark skinned Latin Americans.2 The disorder has no systemic manifestations. The etiology of EDP, although unclear, is likely related to a cell mediated immune reaction.3 No triggering factor has been consistently identified, although various pesticides, fungicide, and medications have been reported to cause the disorder.1 Clinically, EDP is characterized by slate-grey to blue-brown macules, arranged symmetrically on the trunk, neck, and proximal extremities.4Â
As observed in this case, EDP affects the neck in approximately two thirds of patients; a number of cases have also documented periorbital involvement.5,6Â
Histologic features include vacuolar degeneration of the basal layer, colloid bodies, pigment incontinence, prominent dermal melanophages, and a perivascular mononuclear cell infiltrate in the upper dermis.4
The differential diagnosis in the case includes lichen planus pigmentosus, pigmented contact dermatitis (Riehl’s melanosis), and idiopathic guttate macular hyperpigmentation.   Differentiation from lichen planus pigmentosus (LPP) should be based primarily on clinical findings, as EDP and LPP are often indistinguishable histologically.4 Clinical features of LPP that can help in differentiating it from EDP include: presence of associated pruritus, associated dark-brown papules, asymmetric and sun-exposed distribution of lesions, and mucosal involvement.4
The clinical appearance of idiopathic eruptive macular hyperpigmentation can be very similar to EDP. However, the vast majority of patients described with this disorder are children or teenagers. Lesions of idiopathic eruptive macular hyperpigmentation often spontaneously remit over months to years.7 The histologic features of idiopathic eruptive macular hyperpigmentation include basilar keratinocyte hyperpigmentation and prominent dermal melanophages.7 Importantly, no visible basal layer damage or lichenoid infiltrate is observed.7 This key feature is often helpful in distinguishing idiopathic eruptive macular hyperpigmentation from EDP.Â
Pigmented contact dermatitis is a variant of contact dermatitis, often secondary to fragrances or other cosmetic products. Clinically, as opposed to EDP, pigmented contact dermatitis often has a brown reticulated pattern and mild associated pruritus.8 Importantly, in this condition, the typical manifestations of contact dermatitis (inflammation, edema, spongiosis) are often absent.8 Basal liquefactive degeneration and pigment incontinence are the predominant histologic findings.8
In patients with lesions that are clinically and histologically consistent with EDP, especially in the distribution observed in our patient, it is essential to obtain a careful history to identify a possible culprit allergen. Ramirez, who originally described EDP, postulated that EDP may be a manifestation of pigmented allergic contact dermatitis.1 In a large case controlled study of 39 plantation workers in Panama with typical lesions of EDP, 34 patients were found to have a pesticide allergy to chlorothalonil, compared to 0 out of 41 control patients.1 In this case, a triggering factor could not be identified.