A Dermal Plaque on the Arm

A healthy, immunocompetent female in her 60s presented with a pruritic plaque on her right upper arm. The lesion began as an erythematous papule which enlarged over a 3-week period. She denied systemic features such as myalgia, arthralgia or fevers. There was no history of recent travel, hill walking or insect bites. She denied recent illnesses, weight loss or night sweats and was up to date with routine cancer screening. She had a medical history of only asthma, on regular inhalers. Physical examination revealed a 5 × 5cm erythematous plaque with an elevated border and central desquamation on her right upper arm (Figure 1). There was no axillary lymphadenopathy, and no other lesions were noted on full skin exam. Blood tests revealed a normal full blood count with normal inflammatory markers. Viral serology for HIV, HBV and HCV was negative. Interferon-gamma release assay was negative. Serum protein electrophoresis demonstrated a normal pattern, and the connective tissue disease screen was negative. Borrelia burgdorferi IgG and Treponema pallidum EIA were negative. A skin biopsy was obtained for clinicopathological correlation. Histopathologic examination revealed interstitial and perivascular neutrophilic infiltrate with leukocytoclastic debris and occasional admixed eosinophils (Figure 2A,B). There was no fibrinoid necrosis of the vessels. There was a suggestion of sclerosis of the deep reticular dermis. The differential for the histological findings was broad and included neutrophilic dermatosis, early leukocytoclastic vasculitis (including EED and granuloma faciale), as well as infection. The patient was commenced on dapsone 50 mg once daily, with excellent clinical response (Figure 3). Erythema elevatum diutinum is a rare, chronic form of cutaneous leukocytoclastic vasculitis, first described in 1888 1. It typically presents as red-brown or violaceous papules, nodules or plaques favouring extensor surfaces, with atypical vesiculobullous presentations also described 1. Lesions are usually asymptomatic, but pain or pruritus may occur 2. It can be associated with infective and autoimmune disorders, or as a paraneoplastic phenomenon secondary to haematological or solid-organ malignancy. The term ‘diutinum’ meaning ‘long-lasting’ describes the chronic relapsing nature of the disorder, with the longest reported duration of EED to date being 39 years. Differential diagnoses in this case included Jessner's lymphocytic infiltrate of the skin (JLIS), tumid lupus and acute Lyme disease. Jessner's lymphocytic infiltrate commonly presents as a papule or plaque which enlarges peripherally and can exhibit central clearing 3. Histologic findings are diagnostic; a CD8 + T cell predominant lymphoid infiltrate with perivascular and peradnexal clusters of plasmacytoid monocytes within the dermis 4. Tumid lupus demonstrates similar histologic features to JLIS; periadnexal and perivascular lymphocytic dermal infiltrates which can be differentiated from JLIS by positive Alcian blue stain for dermal mucin 5. Acute Lyme disease can present as a dermal plaque, typically as erythema migrans (EM); an erythematous papule which expands over weeks without central clearing. Histologic examination in EM reveals a perivascular lymphocytic infiltrate mainly composed of CD4+ and CD8 + T cells alongside rare plasma cells 6. The definitive diagnosis of EED is established by histopathology. The typical histopathological finding in early-stage EED is of leukocytoclastic vasculitis. This progresses to fibrosis with aggregates of neutrophils and areas of granulation tissue, thought to prevent early resolution of vasculitis in EED through its susceptibility to damage from immune complex deposition 7. This immune complex deposition in blood vessels is implicated in the pathophysiology of the condition, leading to an inflammatory response and recruitment of leucocytes 1. Direct immunofluorescence may reveal intravascular fibrin deposits or perivascular complement and immunoglobulin deposition 2. Blood tests may reveal raised inflammatory markers or infective, autoimmune or haematological disorders associated with EED 2 such as IgA paraproteinaemia. Effective treatments include the anti-neutrophil agent dapsone, as other treatment options are limited. Dapsone monotherapy has a reported efficacy rate of 80% in improving or clearing cutaneous EED lesions alongside improvement in extra-cutaneous manifestations 2. Topical or intralesional steroids have been trialled with varying results. Few studies have shown the limited effectiveness of other agents such as prednisolone, colchicine or tetracycline antibiotics. Even with dapsone therapy, treatment courses are long and relapse is common 2. This case of EED highlights the importance of clinicopathological correlation and consideration of a wide range of differential diagnoses which can present as a solitary dermal plaque. EED has a broad spectrum of presentations with multiple possible underlying triggers. In this case, we are happy to report excellent clinical response with clearance to low-dose dapsone, the mainstay of treatment in this disorder. Claudine Howard-James: data curation, writing – original draft, writing – review and editing, methodology, investigation, visualisation, corresponding author. Aisling Nolan and Graham Woods: histopathological images and descriptions. Ian McDonald: writing – review and editing, visualisation, methodology, investigation, project administration, supervision. The authors received no specific funding for this work. The authors have nothing to report. The patient in this manuscript has given written informed consent for participation in the study and the use of their de-identified, anonymised, aggregated data and their case details (including photographs) for publication. Ethical approval: Not applicable. The authors declare no conflicts of interest. The data that support the findings of this study are available from the corresponding author upon reasonable request.