Primary Syphilis of the Finger

To the Editor:

Syphilis is a sexually transmitted infection (STI) caused by Treponema pallidum (TP) and characterized by cutaneous, mucous, and systemic involvement.¹ The first stage of the disease is defined by a solitary, indurated, painless nodular-ulcerative lesion appearing at the site of TP inoculation.¹ The incidence of extragenital primary syphilis ranges from 2% to 10%² and it has been described on almost any site of the body.³

A 36-year-old homosexual man came to our Department for an asymptomatic ulcerative lesion of the right hand forefinger, which appeared 3 weeks before; despite a therapeutic regimen with oral ciprofloxacine 500 mg twice daily for a week plus topical gentamicine suggested by the family doctor, the lesion increased. Considering the clinical course and his sexual habits, the patient referred to our centre for STIs he reported sexual contacts between his finger and the anus of an occasional partner about 3 weeks before. Clinical examination revealed a roundish, well-demarcated ulcerative lesion, 1 cm in diameter, with erythematous and scaling surrounding skin (Fig. 1). No other cutaneous or mucous lesions were observed and no regional adenopathy was detectable. Routine laboratory investigations requested by the family doctor were normal; the patient was an office worker and anamnesis was negative for local traumas and/or insect bites. Before performing a skin biopsy, we decided to make specific examinations for syphilis. The dark-field microscopic examination was negative but serology revealed a reactive TPPA at a titre of 1:80 and a reactive VDRL at a titre of 1:8; moreover, the ulcer swab tested with Nucleic Acid Amplification Test for TP (we used the Amplisens Treponema pallidum-AA503 Kit—Nuclear Medicine Srl) was positive. A diagnosis of extragenital primary syphilis was made, and the patient was treated with intramuscular Benzathine penicillin G 2.4 million units in single dose. Enzyme-linked immunosorbent assay test for HIV was performed giving negative results.

Figure 1.: Roundish, well-demarcated ulcerative lesion of the forefinger, consistent with a syphilitic chancre.

In the past, primary syphilis of the fingers was often diagnosed in physicians and nurses as a consequence of the contact with infectious chancres; nowadays it is very unusual and is caused by the contact with genital lesions during sexual practices.² The diagnosis of extragenital syphilis is very difficult, notably in case of atypical localization like the hands, because physicians are not used to think about a STI in case of extragenital lesions. In our case, the family doctor suggested an aspecific antibiotic therapy, but the clinical course, the patient's sexual habits, and the patient's suspicion itself lead us to the diagnosis. The dark-field microscopy examination failed in revealing TP in the ulcerative lesion but this could depend on the local antibiotic therapy previously administered; in such cases, Nucleic Acid Amplification Test, more sensitive and specific, could be very useful and should be considered as a routine examination in clinics for STI.⁴ The incidence of syphilis is increasing and so a high index of suspicion is needed⁵; therefore, we suggest that any asymptomatic ulcerative lesion, suddenly spreading anywhere in the body, should be investigated having the suspect of a primary syphilis in at risk people.

Stefano Ramoni, MD

Marco Cusini, MD

Vinicio Boneschi, MD

Chiara Galloni, MD

Silvia Marchetti, MD

Dipartimento di Anestesiologia, Terapia Intensiva e Scienze Dermatologiche

Università degli Studi di Milano–Fondazione IRCCS Ca' Granda

Ospedale Maggiore Policlinico

Milano, Italy