Unilateral penile swelling: an unusual presentation of primary syphilis?

Case Report

A 39-year-old homosexual man presented to a genitourinary clinic with a three-day history of acute pain in his left groin and swelling along the left side of the shaft of his penis. He had initially consulted his general practitioner (GP) on the first day of symptoms. His GP prescribed amoxicillin 500 mg three times per day for presumed cellulitis and also suspected a strangulated inguinal hernia. He was sent to Accident and Emergency where a strangulated hernia was excluded. His symptoms persisted and he began to complain of mild frequency of urine. But he had no dysuria, penile discharge, blisters or ulcers. The unilateral swelling along his penile shaft worsened and became painful. He had no constitutional symptoms.

His last sexual contact was six weeks previously with a regular partner of 12 weeks duration. He reported unprotected oral intercourse and one episode of protected receptive anal intercourse. He had no other partners during these 12 weeks. There was no history of sexually transmitted infections and he had never been tested for syphilis in the past.

Examination revealed a single tender, swollen left inguinal lymph node. There was a mild tenderness on palpation of his left testicle and left epididymis. The left side of his glans and penile shaft was swollen, oedematous and very tender. The right side, however, was completely normal. There were no penile discharge, ulcers and blisters seen. There were no other skin lesions.

Microscopy of his urethral swab revealed non-specific urethritis. In view of the history and findings, he was treated for non-specific urethritis and epididymo-orchitis with a two-week course of doxycycline.

Three days later, his syphilis serology showed treponemal enzyme immunoassay positive, Treponema pallidum particle agglutination assay positive and rapid plasma reagin positive titre of 1:128. Tests for gonorrhoea and chlamydia were negative. He was called back to clinic for treatment. By then, the penile swelling had subsided markedly and a diagnosis was made of probable primary syphilis presenting as penile swelling. He was given a four-week course of doxycycline 200 mg twice daily and made a full recovery.

Discussion

Primary syphilis is characterized by a solitary, painless, indurated ulcer (chancre) at the initial site of inoculation of T. pallidum. But the lesion can also be multiple, painful and in extra-genital sites. It is often associated with inguinal lymph nodes that are enlarged, rubbery, painless and discrete.^1,2 Occasionally, primary syphilis can present without ulceration, for example as a rectal mass^3,4 or as a non-ulcerating papule.

It is very likely that this patient had primary syphilis with a probable urethral chancre. Intra-urethral chancres are a recognized but rarely diagnosed presentation of primary syphilis. There are very few reports in the current literature describing urethral chancres. ⁵ They may present with urethral thickening and non-gonoccocal urethritis as in this case. Primary chancres in the distal urethra may be visible when the urethral meatus is held apart, whereas chancres that are more proximal along the urethra are not visible from the meatal opening. The latter give rise to dysuria, penile discharge and tenderness on external pressure without an obvious ulcer. This may pose a diagnostic challenge clinically until syphilis serology is available.

It is important to acknowledge that there are a number of causes of penile oedema that need to be considered, which can be divided broadly into sexual and non-sexual causes. ^{6 8} Sexual causes include sexually transmitted infections, prolonged or vigorous sexual intercourse and fellatio and condom dermatitis. Non-sexual causes include infections, injury, filariasis, lymphocoele, varicocoele, paraphimosis, fixed drug eruption, insect bite, contact dermatitis and carcinoma.

Learning Point

All clinicians should consider primary syphilis as a possible cause of penile swelling and inguinal lymphadenopathy.

This patient gave written consent for this case to be published.