Clinicopathological,dermoscopic,and ultrastructural observation of annular secondary syphilis on the penis

Introduction

Secondary syphilis is characterized by a generalized, nonpruritic maculopapular rash with a coppery hue.^1–3 However, atypical cutaneous manifestations (nodular, nodulo-ulcerative, annular, pustular, framboesiform, photosensitive eruption) account for 30% of syphilis and have variable histopathological findings and differential diagnoses, ¹ which can lead to a diagnostic challenge and therapeutic delay. We describe herein the clinicopathological, dermoscopic, and ultrastructural features of secondary syphilis with annular lesions on the penis.

Case report

A 29-year-old man presented with several, asymptomatic, annular, erythematous plaques on the penis for one month. He had unprotected heterosexual sex three months ago and reported no history of previous genital ulceration. Physical examination showed five erythematous annular plaques with slightly raised scaly borders and one erythematous scaly plaque measuring 7–15 mm in diameter on the penis (Figure 1(a)). Dermoscopy revealed peripheral dotted and short linear vessels and white scaling with a relatively clear central area in an erythematous annular plaque (Figure 1(b)), and central dotted and short linear vessels with circular scaling edges in an erythematous scaly plaque. There were no other mucocutaneous lesions or inguinal lymphadenopathy. A biopsy of an annular plaque displayed mild hyperkeratosis, parakeratosis, psoriasiform acanthosis, and focal basal vacuolar degeneration with lichenoid, perivascular, and periadnexal infiltrate of lymphohistiocytes and plasma cells in the superficial dermis (Figure 1(c)). Silver stain showed several spirochetes in the lower epidermis and superficial dermis (Figure 1(d)). Electron microscopy revealed a few intercellular and intracytoplasmic spirochetes in the basal epidermis (Figure 1(e)) and free spirochetes in the papillary dermis (Figure 1(f)). Rapid plasma reagin and Treponema pallidum particle agglutination assays were positive, and HIV serology was negative. A diagnosis of annular secondary syphilis was made. The lesions disappeared in ten days after intramuscular benzathine penicillin (2.4 million units) once a week for three weeks. Rapid plasma reagin titer reduced from 1:64 to 1:1 at six-month follow-up.

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Figure 1.

Clinicopathological, dermoscopic, and ultrastructural observations of annular secondary syphilis. (a) One erythematous annular plaque with slightly raised scaly borders and one erythematous scaly plaque on the dorsal prepuce of the penile shaft. (b) Polarized dermoscopy of the erythematous annular plaque showed peripheral dotted and short linear vessels and white scaling with a relatively clear central area (original magnification: ×30). (c) Hematoxylin and eosin stain revealed partial parakeratosis, psoriasiform acanthosis, and focal basal vacuolar degeneration and hyperpigmentation in the epidermis, and dermal edema, endothelial swelling of the dilated blood vessels, and lichenoid and perivascular infiltrate of lymphohistiocytes and plasma cells in the superficial dermis (original magnification: ×200). (d) Warthin–Starry stain showed a few spirochetes (arrows) in the lower epidermis (original magnification: ×400). (d,e) Electron microscopy displayed one intracytoplasmic spirochete (asterisk) in one basal keratinocyte (e) and one free spirochete (asterisk) in the papillary dermis (f). The electron-lucid halo was seen around the microorganisms (uranyl acetate and lead citrate stain; original magnification: ×15k).

Discussion

Annular syphilis is more common in children and black patients during the late secondary stage, and often involves the scalp, face, palm, sole, and intertriginous and genital regions.^1–4 Appearances may range from mildly raised lesions with scaly borders to verrucous plaques. ¹ Localized annular syphilis on the genitalia has been rarely reported in HIV-negative cases, and should be distinguished from granuloma annulare, annular lichen planus, annular psoriasis, scabies, and dermatophytosis.^2–4

The main dermoscopic findings of secondary syphilis are Biett’s collarette and yellow-orangish hue, while the vascular pattern is indefinite.^5–7 Typical Biett’s collarette presents as a circular, thin, scaling edge progressing in an outward direction and surrounded by an erythematous halo. ⁵ The orangish background may originate from erythrocyte extravasation and hemosiderin deposition in the dermis. ⁶ However, regularly dotted vessels (typical hallmark of psoriasis) were observed in a case of annular scrotal plaque, ² while Biett’s collarette and orangish background were absent in our case. Therefore, although its diagnostic value is currently limited for secondary syphilis, dermoscopy is useful in the differential diagnosis with other common inflammatory dermatoses. Genital psoriasis displays regularly distributed dotted vessels with little or absent scaling, lichen planus features Wickham striae and peripheral dotted vessels, and granuloma annulare manifests as unfocused vessels and yellowish structureless areas over pinkish-reddish background. ⁸

Although histopathological features of our case including psoriasiform acanthosis, elongated rete ridges, vacuolar and lichenoid inflammation, plasma cell infiltrate, and endothelial swelling suggest the possibility of syphilis; ⁹ these findings need to be validated by silver and immunohistochemical staining and serology. Silver stain and immunohistochemistry with anti-T. pallidum antibody can visualize the spirochetes in the mucocutaneous lesions, and their diagnostic sensitivity is 31–71% and 74–94%, respectively. ¹⁰ Immunohistochemistry and electron microscopy show that the spirochetes in secondary syphilis are abundant in the lower epidermis and scant in the papillary dermis.^10,11 On electron microscopy, the spirochetes contain central axial filaments and peripheral electron-lucid halo, and are located in intercellular spaces and membranal invaginations.^10,11

In conclusion, the dermoscopic findings are nonspecific in genital annular syphilis and larger studies could facilitate their clinical relevance in syphilis.