Histopathologic features distinguishing secondary syphilis from its mimickers - 07/11/19

Doi : 10.1016/j.jaad.2019.07.011

Alexandra Flamm, MD ^a,^⁎ , Veronica Merelo Alcocer, MD ^a, Viktoryia Kazlouskaya, MD, PhD ^b, Eun Ji Kwon, MD ^c, Dirk Elston, MD ^d
^a Department of Pathology and Dermatology, Penn State Hershey Medical Center, Hershey, Pennsylvania
^b Department of Dermatology, SUNY Downstate Medical Center, Brooklyn, New York
^c Dermpath Diagnostics New York, Port Chester, New York
^d Department of Dermatology, University of South Carolina, Charleston, South Carolina

^∗Reprint requests: Alexandra Flamm, MD, Department of Dermatology, Penn State Hershey Medical Center, Mail Code HU14, 500 University Dr, Hershey, PA 17033.Department of DermatologyPenn State Hershey Medical CenterMail Code HU14, 500 University DrHersheyPA17033

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Abstract

Background

Syphilis is often misdiagnosed clinically, and biopsies might be required.

Objective

To determine histopathologic features that distinguish secondary syphilis from pityriasis lichenoides (PL), pityriasis rosea (PR), and early mycosis fungoides (MF).

Methods

Histopathologic features of 100 cases of syphilis, 110 cases of PL, 72 cases of PR, and 101 cases of MF were compared.

Results

Elongated rete ridges and interstitial inflammation favor syphilis over PL (likelihood ratios 3.44 and 2.72, respectively), but no feature reliably distinguishes between them. Secondary syphilis and PR can be distinguished by neutrophils in the stratum corneum, plasma cells, interface dermatitis with lymphocytes and vacuoles, and lymphocytes with ample cytoplasm. Plasma cells and lymphocytes with ample cytoplasm are rare in early MF and can be used as distinguishing features.

Conclusions

Histopathologic features characteristic of syphilis can be seen in PL, PR, and early MF. Distinguishing syphilis from PL can be difficult histologically, and a high index of suspicion is required. Although elongation of rete and interstitial inflammation favor syphilis, plasma cells (historically considered a significant feature of syphilis) are often encountered in PL. Vacuolar interface dermatitis with a lymphocyte in every vacuole is considered characteristic of PL, but this feature appears to be more common in syphilis.

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Key words : dermatopathology, mycosis fungoides, pityriasis lichenoides, pityriasis rosea, secondary syphilis, syphilis

Abbreviations used : LR, MF, PL, PR