Images of Memorable Cases: Case 10 This young adult experienced the acute onset of tender, enlarged lymph nodes in both groins. 10. Lymphogranuloma venereum A sexually transmitted infection caused by Chlamydia trachomatis. In this patient, affected lymph nodes above and below the inguinal fold created the “groove sign” bilaterally. Although not pathognomonic, this sign is characteristic of lymphogranuloma venereum and should immediately suggest the diagnosis.