Progressive Linear Bullous Eruption in a Young Athlete: A Diagnostic Challenge

A 16-year-old semi-professional rugby athlete presented with a progressive, tense bullous eruption with crusts, predominantly in a linear pattern on the left arm (Figure 1). The eruption began as localised papulovesicles on the left antecubital fossa approximately 2 weeks ago and later disseminated with scattered lesions on the trunk and extremities. Initial treatment with intravenous flucloxacillin for presumed bullous impetigo yielded incomplete improvement despite adherence to oral stepdown therapy, prompting re-presentation. The patient was otherwise well, with no systemic or infectious symptoms and no recent drug exposures beyond prescribed antibiotics. Examination revealed a characteristic ‘string of beads’ pattern (Figure 1). What are the differential diagnoses? The differential diagnoses in an adolescent athlete include infectious causes in bullous impetigo, herpes gladiatorum due to herpes simplex virus type 1 (HSV-1), bullous arthropod reaction and bullous tinea corporis [1-3]. Rare infectious mimics can include Nocardia, atypical mycobacteria and deep fungal infections [3-5]. Acute contact dermatitis presenting as bullae due to topical adhesives, topical medicaments or sports taping and strapping is another possible differential diagnosis [6]. Autoimmune differential diagnoses can include linear IgA bullous dermatosis and epidermolysis bullosa acquisita [7, 8]. The initial ‘string of beads’ pattern on examination and incomplete response to previous antibiotics treatment raised suspicion for linear IgA bullous dermatosis (LABD) [9]. Empirical treatment with intravenous antibiotics to cover for bullous impetigo, prednisolone and dapsone for the suspicion for LABD, and topical corticosteroids with wet dressings for symptom management were initiated while awaiting further investigation results [9]. After initial stabilisation, biopsy revealed intraepidermal vesicles with features of viropathic changes including apoptotic keratinocytes with multinucleation, moulding of nuclei and margination of chromatin [10], dense lymphocytic infiltrates, absence of neutrophils, and negative direct immunofluorescence (Figure 2) [10]. Viral PCR confirmed HSV-1. Bacterial swab was positive for Staphylococcus aureus on initial ED presentation, but the bacterial swab on re-presentation was negative. The negative bacterial swab results could be influenced by recent antibiotics prior to re-presentation. The diagnosis is herpes gladiatorum with likely secondary bullous impetigo mimicking linear IgA bullous disease. Immunosuppressants were discontinued, and the patient was treated with oral valaciclovir, cefalexin and wet dressings. At 2-week follow-up, affected areas showed re-epithelialisation with residual post-inflammatory changes. This case highlights an atypical presentation of herpes gladiatorum due to the ‘string of beads’ pattern on clinical examination, complicated by potential secondary bullous impetigo, mimicking LABD. The patient's athletic activities likely predisposed him to secondary infections due to frequent trauma and compromised skin integrity [11, 12]. This case underscores the importance of maintaining a broad differential for bullous eruptions and integrating clinical, pathological, and microbiological findings for accurate diagnosis. Early recognition and targeted therapy are critical to avoid unnecessary immunosuppression and ensure optimal outcomes. Open access publishing facilitated by The University of Newcastle, as part of the Wiley - The University of Newcastle agreement via the Council of Australasian University Librarians. The authors have nothing to report. The authors declare that the research presented in this manuscript adheres to the ethical principles outlined by the Human Research Ethics Committee (HREC). All procedures involving human participants were conducted in accordance with the ethical standards of John Hunter Hospital in Australia and the Declaration of Helsinki (1964), as revised in 2013. Patient informed verbal consent has been obtained for the publication of this case image. No patient identifying information is included as a part of this submission. Patient written informed consent was obtained for the publication of this case image in accordance with the journal's patient consent policy. No animals were involved during this study. The authors declare no conflicts of interest. Data sharing not applicable to this article as no datasets were generated or analysed during the current study.