Differential diagnosis of perianal herpes: sexual abuse or autoinoculation?

A 13-year-old boy was referred to the forensic department for suspicion of unreported sexual abuse due to the presence of perianal dermatologic lesions. The forensic examination revealed perianal herpes simplex virus type 1 (HSV-1) lesions using nucleic acid amplification by polymerase chain reaction (PCR) outside of any traumatic or other dermatological lesions. Repeated serological tests for sexually transmitted infections (STIs) were negative. However during the psychological interview, the child reported penile touching by a 15-year-old boy at least one week earlier. Both the examination of the alleged aggressor and the serological tests for HSV and STIs were negative. This case presents a challenge in differential diagnosis and highlights the difficulty in interpreting medical findings in cases of suspected sexual abuse.