The FP diagnosed erythema multiforme (EM) in this patient based on the target lesions with central epithelial disruption on his palms. In this case, the EM was due to the herpes simplex outbreak on the patient’s lips (herpes labialis) that had occurred about a week earlier.
EM is 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 ≥ 60% of cases.
The patient did not know that cold sores were due to herpes simplex and most oral HSV is due to HSV1 infection. He acknowledged that he experienced cold sores about every 2 months that were usually related to stress or exposure to intense sunlight. The FP recommended that the patient avoid intense sunlight (midday sun avoidance; wearing sunscreen and hats) and use lip protection with at least an SPF of 15. As the lip lesions were > 90% healed, there was no reason for the FP to prescribe an antiviral agent. The FP did, however, offer a prescription for valacyclovir to be used at the first signs of an oral herpes outbreak to avoid another case of EM (2000 mg by mouth every 12 hours x 2 doses). For symptomatic relief of the EM, the physician prescribed a 15 g tube of 0.1% triamcinolone cream to be applied to the lesions twice daily.
Photo courtesy of the University of Texas Health Sciences Center, Division of Dermatology 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, eds. Color Atlas and Synopsis of Family Medicine. 3rd ed. New York, NY: McGraw-Hill; 2019:1161-1168.
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