Introduction: Secondary syphilis is well-known for its protean cutaneous manifestations and therefore very easy to be misdiagnosed.
Aim: The current study was to observe the frequency of histopathological features characterizing secondary syphilis, and summarize the diseases most likely to be misdiagnosed.
Material and methods: In this study a total of 129 pathological specimens from 114 patients with biopsy-proven secondary syphilis were retrospectively analysed and categorized according to clinicopathologic characteristics. The frequency of histopathological features characterizing secondary syphilis were analysed by comparison with clinical features.
Results: We found that in a single sample there is at least one feature or at most 13 features exist concurrently, and most demonstrated between 5 and 9 diagnostic features. Plasma cells (97.6% overall vs. 94.0% ≤ 6 features), endothelial swelling (86.8% vs. 74.0%), epidermis hyperplasia (73.6% vs. 62.0%) especially irregular acanthosis, lymphocytes infiltration (71.3% vs. 52.0%) and interstitial patterns (69% vs. 72.0%) were the most common findings in all cases as well as in cases with ≤ 6 features. Granulomatous inflammation is an uncommon histopathologic pattern in secondary syphilis (12.4%). The rash morphologies of our biopsies mainly manifesting as macules and maculopapules were more likely to have 6 or fewer features, which were not only easily misdiagnosed for pityriasis rosea, tinea and erythema multiforme, but also mostly taken from the trunk and genitalia. Atypical morphologies can be combined with plasma cell infiltration and T. pallidum immunohistochemical stain to confirm the diagnosis.
Conclusions: In this study plasma cells from superficial and deep perivascular distribution to nodular infiltration were a crucial clue for diagnosis of secondary syphilis.
Keywords: endothelial swelling; histopathology; misdiagnosis; plasma cells; secondary syphilis.
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