Cai-Chou Zhao, Zheng Zhang, Song Zheng, Jiu-Hong Li?

Department of Dermatology, No. 1 Hospital of China Medical University, Shenyang, Liaoning 110001, China.

Introduction

Syphilis is a sexually transmitted disease that is common worldwide.Because of its complicated and variant clinical manifestations,it can be challenging to diagnose.Here,we report a case of annular syphilis, which is an uncommon form of secondary syphilis, on a rare region. This interesting case provides clinicians with knowledge that may aid them in making correct and differential diagnoses.Our work also emphasizes upon the need to pay more attention to uncommon clinical presentations of syphilis.

Case report

A 21-year-old Chinese male presented with a 30-day history of annular erythematous scaly itching lesions on the penis in the Department of Dermatology, No.1 Hospital of China Medical University. The eruptions had begun as papules on the penis, and they had progressively expanded into annular erythematous scaly lesions.The patient was initially diagnosed at a local clinic with a dermatophyte infection and was treated with topical antifungal agents for 3 weeks.Although the itching improved following this treatment, the skin lesions increased in size.

His physical examination results were normal, and a fugal examination yielded a negative result. A skin examination revealed two annular erythematous scaly plaques with central clearing and defined borders on the penis,while no skin lesions were observed on the mucous membranes or other skin surfaces (Fig. 1A). The patient was otherwise healthy and had no family history of similar symptoms.

A biopsy specimen was taken from the margin of lesion,and histology of the specimen revealed a perivascular infiltrate of predominantly lymphocytes also containing significant populations of plasma cells, eosinophils, and neutrophils in the upper dermis along with psoriasiform epidermal hyperplasia and focal liquefaction degeneration of the basal cell layer(Fig.1B).The results of two serologic tests suggested a syphilis infection. The Treponema pallidum particle agglutination assay yielded a positive result, as did a test for rapid plasma reagin (positive at 1:32); evidence of HIV was not detected. After repeated questioning,the patient admitted a history of unprotected sexual encounters with heterosexual partners over the previous 2 years.He did not experience any fever,malaise,headache, or arthralgia.

Based on the patient’s history of unprotected sexual behaviors, clinical manifestations, and histological and serological findings, he was diagnosed with localized annular secondary syphilis. The patient received intramuscular benzathine penicillin G at a dose of 2.4 million units per week for three weeks.Over the treatment period,the skin lesions subsided completely.At a follow-up of 12 months,there was no relapse of the disease,and the results of rapid plasma reagin and HIV tests were negative.

Discussion

The most common typical skin lesions of secondary syphilis are generalized,papulosquamous eruptions1with a coppery hue and sharply demarcated margins that can involve the trunk and extremities,including the palms and soles. Up to 29.6% of skin manifestations of secondary syphilis demonstrate atypical morphology,2which includes annular, pustular, nodular, nodular-ulcerative,berry-like, corymbiform, photosensitive systemic lupus erythematosus-like, lues maligna, leukoderma, and chancriform presentations.3Typical secondary syphilis is not usually associated with pruritus, but studies have shown that 42%of patients with secondary syphilis had itching.4

Annular secondary syphilis is a less type of secondary syphilis,the prevalence of which is approximately 5.7%–13.6%.4-5It often occurs in children and dark-skinned people,and it is mainly located on the cheeks,often close to the angle of the mouth.In rare cases,it can scatter over the penis, feet, and legs.6

Because the skin lesion in this patient was located only on the penis, the initial differential diagnoses mainly included annular lichen planus, psoriasis, and dermatophyte infection. Annular erythematous scaly lesions with itching can also be seen in psoriasis. However, while the scales in psoriasis are dry, white, and shiny, there is an oozing of blood from the capillaries (Auspitz’s sign) after removal of the scales, whereas this does not occur in secondary syphilis. Because Auspitz’s sign was not observed in our patient, psoriasis was ruled out as the likely diagnosis.The defining skin feature of annular lichen planus is composed of small papules with central hyperpigmentation, and the histological features of this condition include a band-like lymphocytic infiltration at the dermal-epidermal junction,a lack of plasma cells,and negative serology for syphilis. Annular lichen planus was excluded based on the significant amount of plasma cells observed in the biopsy and the positive serological results for syphilis.Finally,because the fugal examination for this patient yielded negative results and the antifungal treatment did not result in any improvement,the diagnosis of dermatophyte infection was also excluded.

As a noninvasive tool,dermoscopy can reveal epidermal and dermal structures, but dermoscopic observation cannot establish an accurate diagnosis for syphilis.7Additionally, although microscopic examination is useful to determine dermatophyte infection, its findings may be less specific for secondary syphilis than they are for primary syphilis.8Detecting Treponema pallidum by immunohistochemistry and silver staining in a biopsy specimen can provide defined proof of the diagnosis for syphilis; unfortunately, some cases of syphilis have negative results from these assays.9Therefore, serologic testing remains essential in establishing the diagnosis of syphilis.

Annular secondary syphilis generally has a good response to penicillin treatment. In the present case, the skin lesions subsided completely within one month, and there was no recurrence after one year of follow-up.6-7,10