Intertriginous Secondary Syphilis: A Case Report of a Rare Presentation

To the Editor: Syphilis, a sexually transmitted infection caused by Treponema pallidum, has reported a tremendous upsurge of incident cases worldwide.1,2 Syphilis has an atypical presentation, and its diagnosis remains a pertinent challenge.2,3 We present a case of secondary syphilis confined to the intertriginous areas without plasma cell infiltration, which is difficult to diagnose both clinically and pathologically. A 58-year-old woman presented with a 2-week history of pruritic lesions with relatively well-defined erythematous to brownish mottled patches in the bilateral axillae, antecubital fossae, popliteal, and inguinal areas without palmar involvement (Fig. 1A-G). The lesions were recurrent despite initial topical corticosteroid therapy. The patient was taking unspecified cardiovascular medications and supplements and denied any recent sexual contact. The lesions were initially treated as symmetric drug-related intertriginous and flexural erythema. However, a biopsy was performed when the therapeutic trials of antihistamines and topical corticosteroids were inadequate. Histopathology showed irregular acanthosis, spongiosis, lymphocyte, and neutrophil exocytosis in the epidermis, and a mild to moderate superficial papillary dermal perivascular and interstitial infiltrates composed of lymphocytes, histiocytes, and neutrophils (Fig. 2A). No plasma cells were present in the dermal infiltration. Diffuse exocytosis of neutrophils was noted particularly in the lower epidermis (Fig. 2B) raised the possibility of syphilis. Immunohistochemical findings of T. pallidum highlighted numerous treponemes in the lower epidermis (Fig. 2C). For follow-up diagnosis, rapid plasma reagin titer (1:128) and treponemal test (22.78 S/CO) were conducted for serological confirmation. HIV (HIV) screening was nonreactive. Treatment for secondary syphilis was initiated with excellent results.FIGURE 1.: Intertriginous clinical presentation of syphilis with relatively well-defined erythematous to brownish mottled patches in the (A–B) antecubital, (C–D) axillary, (E) popliteal, and (F–G) inguinal areas.FIGURE 2.: Histopathological examination (incisional biopsy obtained from the right axilla) showed (A) a mild to moderate superficial infiltration in the papillary dermis with irregular epidermal acanthosis. B, A closer view showed irregular acanthosis and spongiosis in the epidermis. A prominent neutrophil exocytosis is present in the lower epidermal layers. C, Treponemal pallidum immunohistochemical examination showed numerous treponemes in the lower epidermis, corresponding to the site of neutrophil exocytosis (hematoxylin and eosin, A × 100×; B × 400×; C × 400×).Atypical cutaneous manifestations of syphilis are found in all stages of the disease. Severe, persistent, or ulceronecrotic lesions, early onset of systemic involvement, and overlapping clinical stages are usually seen in patients with HIV infection. However, HIV-seronegative patients may present with a variety of pleomorphic lesions from follicular, vesicular, pustular forms, and rarely malignant syphilis.3 To date, a purely intertriginous involvement of secondary syphilis, clinically mimicking atopic dermatitis, contact dermatitis, or drug reaction, has not been reported. Histopathological finding of T. pallidum is crucial in diagnosing these uncommon forms. Pathologically, most known patterns include psoriasiform lichenoid infiltration and granulomatous dermatitis. Presence of dyskeratotic cells, neutrophils in the stratum corneum, plasma cells in the dermal infiltration, elongated rete ridges, and interstitial inflammation are important pathological findings.4,5 Neutrophil exocytosis in the stratum corneum is suggestive of cutaneous infectious disease such as superficial fungal infection. However, neutrophil exocytosis observed in the middle to lower epidermal layers, corresponding to spirochetes location, is highly suggestive of syphilis.5 This should prompt immunohistochemical and serological tests for confirmation. The pathological hallmark of presence of plasma cells in secondary syphilis might be absent in these atypical cases. This case study highlights a rare intertriginous involvement in secondary syphilis. Diffuse neutrophil exocytosis is a good indicator of syphilis and should prompt treponemal immunohistochemical or serological studies for confirmation. In the context of rising incidence of local syphilis, any recalcitrant dermatitis should raise suspicion for syphilis.