Knife-Cut Sign – A Distinctive Presentation of Herpes Simplex Virus in an Immunocompetent Patient

Dear Editor, Herpes simplex virus (HSV) is a prevalent cause of genital ulcers, with varying manifestations depending on the immune status and recurrences.[1] It typically presents as multiple, painful, closely grouped vesicles, that break down to form ulcers with polycyclic margins. However, the linear intertriginous ulcer and fissure in a knife-cut pattern is a rare presentation in patients with HSV and underlying immunosuppression. We report a patient presenting with knife-cut ulcers without any underlying immunosuppression. A 47-year-old female with no comorbidities presented with deep fissures over the groin, vulva, and abdominal fold for 1-month duration. The lesion started as erythema followed by linear ulcers in the intertriginous area, which did not respond to antifungals and antibiotics. On examination, multiple tiny superficial erosions were present in the vulva and labia majora with well-defined deep linear fissures over the lower abdominal fold, vulval fold, interlabial sulcus, and intergluteal cleft [Figures 1a and 2a]. Differential diagnoses included cutaneous herpetic infection and vulval Crohn’s disease, which can present as knife-cut ulcer. The patient did not have any systemic involvement, or any relevant personal or family history of Crohn’s. The complete blood count and renal and liver function tests were within normal limits. VDRL and HIV were negative. Gram stain did not reveal any organism. Biopsy taken from the edge of the lesion showed nonspecific findings such as epidermal ulceration and dermal perivascular infiltrates. Direct immunofluorescence was negative. Serology for HSV 1 and 2 IgM was negative with a very high positive HSV-2 IgG titer of >1000. Polymerase chain reaction for HSV revealed HSV DNA positive. The diagnosis of herpetic infection presenting as the knife-cut ulcer was made, and the patient was treated with valacyclovir 1 gm tds. Ulcers healed by the 10th day [Figures 1b and 2b].Figure 1: (a) Multiple tiny superficial erosions and linear knife-cut fissures over the vulva. (b) Healed lesion over vulva after 10 days of treatmentFigure 2: (a) Single linear fissure noted over the abdominal fold. (b) Healed lesion over abdominal fold after 10 days of treatmentHSV is commonly associated with oral labial lesions (HSV-1) and genital lesions (HSV-2).[2] However, in immunocompromised patients, HSV-1 and HSV-2 can manifest in different locations, displaying varied morphologies such as larger and deeper lesions with satellite ulcerations. The presence of fissures, hemorrhagic crusts, linear erosions, and erosions with angulated margins can also occur in pemphigus patients with superadded HSV.[3] These atypical presentations may also lead to a prolonged healing period.[1] A distinctive manifestation termed linear erosive herpes simplex or the “knife cut sign” has been recently identified in immunocompromised hosts, posing clinical similarities to cutaneous vulval Crohn’s disease. Originally, the term ‘knife cut’ described linear fissures observed during colonoscopy in Crohn’s disease patients, and can also involve the vulva in metastatic Crohn’s disease.[2,4] In herpetic infection, they are most commonly observed in the inguinal folds, followed by the vaginal fold, interlabial sulcus, infra-abdominal fold, and less often inframammary and gluteal clefts.[2] Both HSV-1 and HSV-2 can be the causative serotypes. To confirm the diagnosis and identify the viral serotype, several laboratory methods may be employed, including polymerase chain reaction (PCR), viral culture, serological tests, and, in some cases, biopsy. However, in our case, we did not do a viral culture, but a positive high serological titer, positive HSV DNA PCR, and rapid response to antivirals helped in confirming the diagnosis. In such patients, systemic antiviral therapy should be continued until the skin lesions have resolved.[2,5] Knife-cut ulcers due to HSV are rare and have been reported in immunocompromised patients. We report this case to highlight that HSV-induced knife-cut ulcers can also occur in an immunocompetent host. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.