Based on the target lesions with central epithelial disruption, the FP diagnosed erythema multiforme (EM) in this patient. He also diagnosed genital herpes simplex in the crusting stage and suspected that it was the inciting event for the EM.
EM is considered a hypersensitivity reaction that is often secondary to infections or medications. Herpes simplex viruses (HSVI and HSV2) are the most common causative agents and have been implicated in at least 60% of cases.
The patient did not know that she had genital herpes simplex but remembered having sores in the genital area that preceded the similar rash a year earlier. This was a case of recurrent EM responding to recurrent herpes simplex.
The patient suspected that she had genital herpes simplex on and off for the past 10 years but lacked health insurance, so she never visited a doctor for treatment. She recently obtained health insurance and was willing to be tested for other sexually transmitted diseases. She also wanted to have a test done to confirm this was herpes simplex. The FP explained that it was unlikely that an antiviral agent would help the current case of herpes simplex and the associated EM because of the late timing, but antiviral medication could help to prevent further outbreaks and decrease transmission to her husband.
The patient was enthusiastic to start valacyclovir 500 mg/d for prophylaxis. For symptomatic relief, the FP prescribed a 30-g tube of 0.1% triamcinolone appointment and instructed the patient to apply it to the EM twice daily. The patient was sent for blood tests for syphilis and HIV; fortunately, both came back negative. The herpes simplex PCR test was positive for HSV2.
On a 1-week follow-up visit, the skin lesions were resolving, and the patient had no further symptoms. The patient said she understood that she should refrain from sexual intercourse if she developed lesions while on prophylaxis.
Photos and text for Photo Rounds Friday courtesy of Richard P. Usatine, MD. This case was adapted from: Milana C, Smith M. Erythema multiforme, Stevens-Johnson syndrome, and toxic epidermal necrolysis In: Usatine R, Smith M, Mayeaux EJ, et al. Color Atlas and Synopsis of Family Medicine. 3rd ed. New York, NY: McGraw-Hill; 2019:1161-1168.
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