DP18: A case of secondary syphilis resembling erythema multiforme: how histopathology clues can avoid a delayed diagnosis

S. Muthiah,¹ C. Moyes,² A. Paton² and S. Sinclair¹

¹Stirling Community Hospital, Stirling, UK and ²Forth Valley Royal Hospital, Larbert, UK

A 45-year-old woman presented with a 3-week history of a nontender, pruritic, maculopapular blistering eruption affecting her head, upper limbs and the palmar aspect of both hands. She was afebrile, complained of a sore throat and had a subungual aphthous ulcer with nontender lymphadenopathy. Based on a recent history of nitrofurantoin ingestion, a clinical diagnosis of erythema multiforme was made. Initial biopsy showed a band-like lichenoid interface reaction with perivascular inflammation. The suggestion of a drug reaction was made, but the presence of plasma cells was noted as unusual. Two weeks later the eruption progressed with prominent translucent nodular lesions involving the upper back and anterior chest and two new vulval lesions. Repeat biopsy showed a wedge-shaped infiltrate of lymphocytes, plasma cells and neutrophils with exocytosis of lymphocytes. Special staining showed no aberrant staining of lymphocytes, predominant T cells and CD56-negative plasma cells with polytypic light chains, raising the possibility of syphilis. A sexual history was taken and she was referred to genitourinary medicine. Serology confirmed secondary syphilis and further histological staining showed numerous spirochaetes in the dermis, epidermis and hair follicle. HIV screening was negative. Secondary syphilis is reported as ‘the great imitator’ owing to its varied presentation and ability to mimic other dermatological conditions, including erythema multiforme. In the absence of risk factors or the classic painless chancre of primary syphilis, diagnosis is challenging and alternatives are typically considered first. Histopathology varies depending on lesion type. Nodular syphilis may display acanthosis, perivascular and periadnexal infiltrate with lymphocytes, plasma cells, histiocytes, and eosinophils. Annular lesions typically consist of lichenoid and focal perifollicular lymphocytic infiltrate with scattered plasma cells and interface dermatitis with lymphocytes, plasma cells, occasional neutrophils and prominent lymphoplasmocytic perivascular infiltrate (Balagula Y, Mattei PL, Wisco OJ et al. The great imitator revisited: the spectrum of atypical cutaneous manifestations of secondary syphilis. Int J Dermatol 2014; 53: 1434–41). Individual histological features of secondary syphilis lack the specificity to provide diagnostic value; however, any combination of plasma cells, endothelial swelling, interstitial inflammation, irregular acanthosis, elongated rete ridges and vacuolar interface dermatitis with lymphocyte predominance should raise suspicion of secondary syphilis (Flamm A, Parikh K, Xie Q et al. Histologic features of secondary syphilis: a multicenter retrospective review. J Am Acad of Dermatol 2015; 73: 1025–30). Early recognition and treatment of syphilis is vital in limiting progression to the tertiary stage, which has a higher morbidity and mortality owing to its neurological and cardiovascular sequelae. Histopathology provides useful clues and pattern recognition helps to prompt serological testing and avoid diagnostic delay.