Supplementary Material for: Histologic Features of Secondary Syphilis

<b><i>Background:</i></b> Secondary syphilis is a sexually transmitted infection, which is referred to as “the great imitator” and has a wide spectrum of clinical manifestations. As a result, it is essential to identify potential secondary syphilis patients with ambiguous clinical manifestation through pathology. <b><i>Objective:</i></b> We sought to analyze the pathological features of secondary syphilis. <b><i>Methods:</i></b> We analyzed 59 biopsy specimens from 56 patients with secondary syphilis. Cases were classified according to the histological characteristics and clinical features. <b><i>Results:</i></b> Necrotic keratinocytes could be observed in 39 of 59 (66.1%) secondary specimens. Plasma cells (86.4%) were the most common finding overall. The presence of <i>Treponema pallidum</i> was detected mostly at the dermal-epidermal junction. There was no statistical significance between pathological features and age, HIV status, or RPR titer. <b><i>Conclusions:</i></b> Necrotic keratinocytes are one of the characteristics of secondary syphilis. The combination of plasma cells, irregular acanthosis, elongated rete ridges, and endothelial swelling should increase the likelihood of syphilis.