Generalized Blastomycosis‐Like Pyoderma in an Immunocompetent Patient

Blastomycosis-like pyoderma (BLP) is a rare, exuberant tissue reaction, usually triggered by bacterial infection, particularly Staphylococcus aureus (SA). Clinically, it presents with verrucous plaques and pustules and histologically with pseudoepitheliomatous hyperplasia and neutrophilic abscesses. Although typically associated with impaired host defense, BLP may also occur in immunocompetent individuals, posing a diagnostic challenge because it resembles deep fungal infections, mycobacterial disease, halogenoderma, and squamous cell carcinoma [1, 2]. We report a long-standing, generalized presentation in an immunocompetent 32-year-old man. A 32-year-old man presented with a progressive eruption of partially pruritic, vegetating, hyperkeratotic plaques and nodules distributed over the trunk and extremities, gradually increasing over more than 8 years (Figure 1). The lesions repeatedly improved during courses of systemic antibiotics prescribed for presumed bacterial skin infection, followed by relapse after treatment discontinuation. He denied relevant comorbidities, regular medication, systemic symptoms, or a history of recurrent infections. There was no history of iodine or bromide exposure. Repeated microbiological swabs obtained from multiple lesional sites consistently yielded SA, whereas repeated mycological investigations, including DNA testing, remained negative. Polymerase chain reaction (PCR) testing for Leishmania and mycobacteria from lesional material was negative, as was an interferon-gamma release assay. Laboratory investigations showed no evidence of immunodeficiency or systemic inflammation, with a normal complete blood count including differential, normal serum immunoglobulins, and unremarkable lymphocyte immunophenotyping by flow cytometry. Human immunodeficiency virus (HIV) testing and lues as well as hepatitis serology were negative. In view of the chronicity and verrucous morphology, alternative infectious and inflammatory differentials were systematically excluded. A full-thickness skin biopsy from a representative plaque demonstrated marked pseudoepitheliomatous hyperplasia with prominent neutrophilic inflammation and abscess formation, without cytological atypia, consistent with BLP (Figure 2). Special stains and tissue cultures for deep fungi and mycobacteria were negative, supporting exclusion of major mimickers [1]. Direct and indirect immunofluorescence studies excluded autoimmune blistering disease. Based on the aforementioned history and clinicopathological findings, a diagnosis of generalized BLP was established. The diagnostic criteria proposed by Su et al. [1] include (i) large verrucous plaques with pustules and elevated borders, (ii) pseudoepitheliomatous hyperplasia with abscesses on histology, and (iii) isolation of at least one pathogenic bacterium, with exclusion of deep fungal and mycobacterial infection. Our patient fulfilled all core criteria, while extensive investigations revealed no underlying immunodeficiency. The pronounced responsiveness to antibiotics, together with repeated isolation of SA, suggests that chronic bacterial colonization or infection combined with an exaggerated neutrophil-driven inflammatory response may be sufficient to sustain the disease phenotype, even in the absence of overt immunosuppression [2]. Therapeutically, antibiogram-guided antibiotics remain the mainstay of treatment; however, relapse is common, and prolonged or repeated courses may be necessary. Adjunctive measures such as antiseptic wound care, debridement, and staphylococcal decolonisation are strongly recommended [2]. In refractory cases, procedural approaches, including serial excisions in localized disease, or systemic retinoids such as acitretin, have been reported to be beneficial, presumably by modulating epidermal hyperproliferation and inflammation [3-5]. In our patient, antibiogram-guided intravenous therapy with ampicillin (4 g daily) combined with sulbactam (2 g daily) was administered for only 3 days, as the patient left the hospital against medical advice. Antibiotic therapy was subsequently switched to oral amoxicillin (500 mg three times daily) for 21 days, resulting in marked clinical improvement. A maintenance strategy including topical antiseptics and decolonization measures was initiated to reduce relapse frequency; however, the patient was subsequently lost to follow-up due to poor adherence. This case underscores that BLP should be considered in chronic vegetating or verrucous eruptions with positive bacterial cultures, even in immunocompetent individuals and in cases of widespread disease. Early recognition, with careful clinicopathological correlation, is crucial to avoid misdiagnosis as a deep fungal infection and to facilitate effective, targeted therapy. The authors have nothing to report. Written informed consent for the publication of the patient's clinical details and images was obtained. The authors declare no conflicts of interest. All crucial data generated or analyzed during this case study are included in this published article.