Diagnosis: Herpes simplex virus
The physician on-call diagnosed candida vaginitis along with a bacterial skin infection, and admitted the patient to the hospital for intravenous (IV) antibiotics. Fortunately, we were there on a medical mission and were consulted on the case.
We diagnosed a primary herpes simplex virus type 2 (HSV-2) infection in this patient, based on the classic presentation of grouped pustules and vesicles on erythematous and swollen labia, and the patient’s complaint of dysuria.
Herpes cultures weren’t available in the hospital, but the clinical picture was unmistakable for HSV infection. Since multiple STIs may occur simultaneously, we ordered a serum rapid plasma reagin (RPR) test for syphilis, and tested her urine for gonorrhea and chlamydia. The tests were negative.
Differential Dx includes other STIs and a fixed drug eruption
Herpes is a common STI and most people don’t have symptoms. In 2012, an estimated 417 million people worldwide were living with genital herpes caused by HSV-2.1
The differential diagnosis for HSV infection includes primary syphilis, chancroid, folliculitis, and fixed drug eruptions.
Primary syphilis (Treponema pallidum) commonly presents with a painless, ulcerated, clean-based ulcer. While the chancre of primary syphilis can sometimes be painful, this patient did not have ulcers at the time of her presentation. Her pustules would likely ulcerate over time, but would not resemble the chancre of syphilis.
Chancroid (Haemophilus ducreyi) is a less common STI than syphilis and HSV infection. It presents with deep, sharply defined, purulent ulcers that are often associated with painful adenopathy. The ulcers can appear grey or yellowish in color.
Folliculitis presents with pustules surrounding hair follicles. Some of the pustules were surrounding hair follicles in this patient’s case, but others were independent of the hair. The patient’s marked swelling and tenderness along with dysuria also did not fit the characteristics of folliculitis.