Atypical Presentation of Localised Annular Secondary Syphilis Confined to Genitals

INTRODUCTION

Syphilis is a multisystem infection caused by spirochaete Treponema pallidum subspecies pallidum. Secondary syphilis (SS) typically occurs 3–12 weeks after infection and compared to the primary stage, it is characterised by a markedly increased proliferation of spirochetes, peak bacteraemia and generalisation of the infection.^[1] Syphilis can present a diagnostic challenge due to its diverse mucocutaneous manifestations, often mimicking various dermatoses – earning it the title of the ‘Great Imitator’. However, it may also exhibit unique, distinctive presentations that deviate from known patterns, demonstrating its ability to manifest in various clinical forms concerning the lesion type, morphology, site, and distribution.

CASE REPORT

A 22-year-old male presented to the Dermatology and Venereology Outpatient Department of a tertiary care hospital with multiple, well-defined, erythematous, annular plaques with central clearing, present over his scrotum and penis along with a lesion of condyloma lata on his penis for the past 5 days. The onset was marked by asymptomatic, erythematous papules which slowly progressed centrifugally to form annular plaques. He was sexually active, with a history of recent unprotected sexual intercourse with his heterosexual partner 2 months before the onset of these lesions. He denied any history of previous genital ulcer or similar lesions in the past. On examination, multiple, non-tender, scaly annular plaques with central clearing having well-defined raised, erythematous borders present over the scrotum and penis. On the ventral aspect of the foreskin, an erythematous, painless, moist plaque with a smooth surface was present suggestive of condyloma lata [Figure 1]. The rest of the mucocutaneous examination was normal apart from the presence of bilateral, enlarged, discrete, painless inguinal lymph nodes.

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Figure 1:

(a) Lesions of annular secondary syphilis on the scrotum. (b) Lesion of Condyloma lata on the foreskin of penis.

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Based on typical morphology of the lesions, our differentials included SS, Annular Psoriasis, Annular Lichen Planus, Granuloma annulare and Dermatophytic infection. However, the presence of recent contact history and enlarged inguinal lymph nodes inclined our diagnosis towards SS. The patient denied biopsy hence, serology was advised which revealed Venereal Disease Research Laboratory (VDRL) reactive in a titre of 1:64 and T. pallidum haemagglutination assay was positive. Rest of the serological profile was negative. He was diagnosed as a case of Localised Annular SS with lesions confined to his genitals only. He was given single dose of Injection Benzathine Penicillin G 2.4 million Units intramuscularly after labelling Antibiotic sensitivity test as negative. His lesions cleared completely 14 days later on his next follow-up visit. His VDRL was repeated 3 months later, and the titre fell four-fold from 1:64 to 1:4.

DISCUSSION

SS is widely known for its ability to create an extensive range of clinically diverse cutaneous lesion.^[2] The most common typical skin lesions of SS are generalised, papulosquamous eruptions with a coppery hue and sharply demarcated margins involving the trunk and extremities, including the palms and soles.^[3]

Previous studies have delineated that up to 29.6% of cutaneous manifestations of syphilis may demonstrate atypical morphology.^[4] The spectrum of reported manifestations of SS includes nodular, nodulo-ulcerative, annular, pustular, lues maligna, frambesiform, corymbose, photosensitive systemic lupus erythematosus-like, leucoderma and chancriform presentations.

Annular syphilitic lesions have been previously documented in the literature, with a reported prevalence ranging from 5.7% to 13.6%.^[3] However, cases where these lesions are exclusively limited to the genital region remain sparsely reported. Annular syphilids are rare and tend to occur more often in children and individuals of African descent, typically during the later stages of SS. They are usually found on the cheeks and near the corners of the mouth, presenting as peripheral erythematous papules with central areas of hyperpigmentation.^[5]

Table 1^[2,3,5-11] compiles previous reports on localised annular SS involving single site with no associated lesions over other mucocutaneous sites.

In our report, the patient denied history of primary lesion which could be because of several reasons, including the chancre being asymptomatic, subclinical infection, healing rapidly or occurring in a hidden area, such as the rectum. As a result, the primary stage may go unnoticed.

In settings with a high prevalence of human immunodeficiency virus (HIV) and associated immunosuppression, atypical presentations of syphilis can obscure the diagnosis and hinder timely treatment. Co-infection with HIV has been reported in up to 25% of syphilis cases.^[4] Syphilis and HIV frequently co-occur due to their common modes of transmission, and each infection can enhance the acquisition and transmission of the other. Syphilitic lesions harbour T cells and dendritic cells that express HIV coreceptors such as CCR5 and DC-SIGN, which further reinforce this epidemiological association.

Therefore, all patients under suspicion should be examined and investigated thoroughly with serological markers to rule out syphilis, and the prozone phenomenon (a false-negative rapid plasma reagin and VDRL test result caused by very high antibody titres) should be considered when initial serologic workup is negative but syphilis is clinically suspected. Apart from serologic tests, other diagnostic methods include dermoscopy, histopathological examination, immunohistochemistry, electron microscopy and reflectance confocal microscopy.

CONCLUSION

In the setting of any unusual clinical presentation, SS should be considered given its ability to progress to advanced stage involving other organs and causing life-threatening complications, if left untreated.