From Ocean Sting to Skin Outbreak: Acute Localised Exanthematous Pustulosis Induced by a Jellyfish Sting

Acute localised exanthematous pustulosis (ALEP) is a rare condition, first described by Prange et al. in 2005 [1]. Initially recognised in a patient with a facial rash that met the diagnostic criteria for acute generalised exanthematous pustulosis (AGEP), ALEP is now considered a localised variant of AGEP. While commonly triggered by hypersensitivity reactions to systemic drugs, ALEP has also been associated with contact mechanisms, such as insect or jellyfish stings [2]. This case report highlights an unusual presentation of ALEP induced by a jellyfish sting. A 6-year-old girl with no significant medical history presented with a 2-day history of perioral pustules and erythema. The mother denied any medication use or known allergies. The eruption started 36 h after the child was stung by a jellyfish (Rhizostoma pulmo) while swimming in the Mediterranean Sea. On examination, the patient exhibited multiple small, confluent, non-follicular pustules on an erythematous and edematous base localised to the perioral skin (Figure 1A,B). There were no vesicles, blisters, or lesions with an eczematous appearance. Laboratory tests were normal, and no bacterial growth was identified from a pustular specimen culture. The patient was treated with betamethasone dipropionate 0.05% topical cream applied once daily. The lesions resolved within 4 days with no recurrence. Histological analysis was not performed in this case, as the mother refused due to the risk of scarring. However, the clinical presentation and the absence of other features such as vesicles, blisters, or bacterial growth, along with the resolution of symptoms following steroid treatment, strongly support the diagnosis of ALEP. ALEP is characterised by the sudden onset of small, non-follicular, sterile pustules on an erythematous and edematous base, typically localised to a specific body area. Due to its clinical and histological similarities to AGEP, ALEP is now considered a localised form of AGEP [1, 2]. The pathophysiology of ALEP is not fully understood, but it is believed to involve a T-cell-mediated immune response, similar to that seen in AGEP. The immune response is triggered by the activation of CD4+ and CD8+ T cells, leading to the production of cytokines such as interleukin-8 (IL-8) and granulocyte-macrophage colony-stimulating factor (GM-CSF). These cytokines promote neutrophil accumulation, resulting in sterile pustule formation [2-4]. The jellyfish species R. pulmo is known to cause both immediate and delayed allergic skin reactions [3, 5]. Its nematocyst constituents, which contain proteins and peptides, trigger innate and adaptive immune responses when they come into contact with human skin [3, 5]. Based on the immune responses described, we hypothesise that ALEP induced by jellyfish stings occurs through an immune-mediated mechanism involving both innate immune activation (via mast cell degranulation, complement activation, and neutrophil recruitment) and adaptive immune responses (driven by T-cell activation and cytokine production). The venom components from jellyfish, such as proteins and peptides from R. pulmo, act as the initiating agents, triggering a cascade of immune events. The activation of mast cells, subsequent T-cell-mediated immune responses, and neutrophil-driven inflammation ultimately lead to the development of pustules and potential liver involvement, characteristic of ALEP. A prior report documented AGEP following a jellyfish sting, further supporting this hypothesis [3]. The diagnostic criteria for ALEP, based on clinical presentation and histopathology, are aligned with the EuroSCAR guidelines for AGEP. Specifically, the criteria for ALEP include the presence of small, non-follicular pustules on an erythematous base, localised to one area, and the absence of vesicles or blisters. It is important to highlight that the diagnosis of ALEP should consider a temporal association with a potential contact mechanism or drug exposure [2, 4]. The EuroSCAR guidelines propose a diagnostic framework for AGEP that can be adapted to ALEP, and we follow these established guidelines in this case [2]. Several published articles report the development of ALEP at the same site as spider bites, though its exact mechanism remains unclear. We believe also that ALEP induced by jellyfish stings may occur through the same mechanism [6]. To the best of our knowledge, our case represents the first documented instance of ALEP attributed to jellyfish stings. Hamza Abu Humaid: conceptualization, investigation, writing – original draft, methodology, writing – review and editing. Aicha Aly: conceptualization, investigation, writing – original draft, methodology, writing – review and editing. Nesrine Ben Salah: conceptualization, investigation, writing – original draft, validation, methodology, writing – review and editing. Mouna Korbi: conceptualization, investigation, writing – original draft. Amal Hamdi: conceptualization, investigation, writing – original draft. Hichem Belhadjali: conceptualization, investigation, writing – original draft. Jameleddine Zili: conceptualization, investigation, writing – original draft, writing – review and editing, validation, supervision. The authors have nothing to report. Written informed consent was obtained from the parent's patient to publish this report in accordance with the journal's patient consent policy. The authors declare no conflicts of interest. Data sharing not applicable—no new data generated.