Histologic features of secondary syphilis: A multicenter retrospective review

Background: Secondary syphilis has a wide spectrum of clinical and histologic manifestations. Objective: We sought to determine the frequency of histopathological features characterizing secondary syphilis, and which are most common in specimens displaying few diagnostic findings. Methods: In a multicenter, retrospective analysis of biopsy-proven secondary syphilis, cases were subcategorized by the number of histologic characteristics present. Results: The 106 cases mostly had 5 to 7 of the features studied. Many features were scarcer in cases with 5 or fewer features, including endothelial swelling (87.7% overall vs 72.4% <= 5 features), plasma cells (69.8% vs 48.3%), and elongated rete ridges (75.5% vs 27.6%). Specimens with 5 or fewer features were more likely to be truncal (61.1% vs 34.4% overall), demonstrate rete ridge effacement (44.8% vs 19.8%), and have pityriasis rosea (33.3% vs 17.2%) or drug eruption (33.3% vs 10.9%) in the clinical differential. An interstitial inflammatory pattern was the most common characteristic of specimens with 5 or fewer features (75.9%). Limitations: This was a retrospective review. Conclusion: The independent value of many histologic features of syphilis may be overestimated. Combinations of endothelial swelling, interstitial inflammation, irregular acanthosis, and elongated rete ridges should raise the possibility of syphilis, along with the presence of vacuolar interface dermatitis with a lymphocyte in nearly every vacuole and lymphocytes with visible cytoplasm.