Dermatology: Practical and Conceptual Research Letter | Dermatol Pract Concept. 2023;13(2):e2023078 1 Eosinophilic Pustular Folliculitis in the Setting of Solid Organ Transplant Immunosuppression Jeffrey Chen1, Colleen J Beatty2, Lauryn M Falcone3, Joseph C English III3, Viktoryia Kazlouskaya2 1 University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States 2 University of Pittsburgh Department of Dermatology/Dermatopathology, Pittsburgh, Pennsylvania, United States 3 University of Pittsburgh Department of Dermatology, Pittsburgh, Pennsylvania, United States Key words: Eosinophilic pustular folliculitis, Ofuji disease, hematopoietic stem cell transplantation, immunosuppression, immune reconstitution inflammatory syndrome Citation: Chen J, Beatty CJ, Falcone LM, English JC, Kazlouskaya V. Eosinophilic Pustular Folliculitis in the Setting of Solid Organ Transplant Immunosuppression. Dermatol Pract Concept. 2023;13(2):e2023078. DOI: https://doi.org/10.5826/dpc.1302a78 Accepted: June 20, 2023; Published: April 2023 Copyright: ©2023 Chen et al. This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial License (BY-NC-4.0), https://creativecommons.org/licenses/by-nc/4.0/, which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original authors and source are credited. Funding: None. Competing interests: None. Authorship: All authors have contributed significantly to this publication. Corresponding author: Viktoryia Kazlouskaya, MD, PhD, University of Pittsburgh, Department of Dermatology and Dermatopathology, Medical Arts Building, 3708 5th Avenue, Suite 500.68, Pittsburgh, Pennsylvania 15213 E-mail: viktoriakozlovskaya@yahoo.com Introduction Eosinophilic pustular folliculitis (EPF) is an inflammatory dermatosis that presents as follicular papulopustules with pronounced eosinophils. Subtypes include classic EPF, infancy-associated EPF, and immunosuppression-associated EPF (IS-EPF). IS-EPF can be sub-divided into HIV-associated (IS/HIV) and non-HIV-associated (IS/non-HIV), with the latter associated with hematologic malignancy, particularly after hematopoietic stem cell transplantation (HSCT) [1]. Herein, we describe a case of IS-EPF in the setting of chronic immunosuppression due to cardiac transplantation. This is the second reported case of IS-EPF associated with solid organ transplant, with the first reported case in 2014 by Kim et al [2]. Case Presentation A 69-year-old male on long-term immunosuppression for cardiac transplantation secondary to non-ischemic cardio- myopathy was evaluated for a diffuse pruritic rash that began several weeks after switching medications from tacrolimus to sirolimus. Skin examination revealed multi- ple erythematous to purpuric papules involving the torso, upper back, and upper extremities (Figure 1). Exanthem- atous drug eruption was favored as the initial diagnosis due to temporal correlation, but graft-versus-host disease, neutrophilic dermatitis, and infectious process were also considered. Histopathological examination revealed mid-dermal perifollicular collections of lymphocytes, histiocytes, and 2 Research Letter | Dermatol Pract Concept. 2023;13(2):e2023078 prominent eosinophils (Figure 2). GMS, Gram, AFB, and PAS stains were negative. Biopsy findings were consistent with EPF, likely associated with the patient’s immunosup- pression. The patient was treated with triamcinolone aceton- ide cream and showed gradual resolution. Conclusions While the pathophysiology of EPF is unknown, prostaglan- din D2 (PGD2) and the IL-36 cytokine family are speculated to be involved in the folliculotropic infiltration of eosino- phils [3,4]. Increases in PGD2 production in EPF have been demonstrated to increase mRNA expression of eotaxin-3, which is an eosinophilic chemotactic factor produced by se- bocytes [3]. IL36α, IL-36β, IL-36γ, and IL36Ra are known modulators of the cutaneous inflammatory response in- volved in eosinophil recruitment. Previous studies showed that IL-36β, IL-36γ, and IL36Ra are upregulated in EPF. Interestingly, the expression of IL36Ra was negatively cor- related with IL-36β and IL-36γ in normal skin, suggesting Figure 1. Erythematous swollen papulopustules on the back. that the expression patterns of IL-36β, IL-36γ, and IL36Ra contribute partially to the eosinophil migration in EPF [4]. Unlike classic EPF, the lesions observed in IS-EPF are less strongly associated with the formation of pustules and do not show the same predilection for the face, as they tend to affect the upper body and extremities [1]. Moreover, IS-EPF responds more favorably to topical or systemic steroids com- pared to classic EPF suggesting different pathogenesis [5]. The clinicopathological features of this case are similar to those observed in IS/non-HIV patients, specifically, cases of IS-EPF that developed after HSCT. A study by Sasaki et al likened the lesions of IS-EPF following HSCT to the devel- opment of IS-EPF in HIV patients caused by immune recon- stitution inflammatory syndrome (IRIS) [6]. In our case, the patient developed EPF after his tacrolimus was switched to sirolimus, which is a decrease in immunosuppression and a step closer to immune reconstitution. Accordingly, this case provides preliminary evidence to suggest a relationship be- tween IRIS and IS-EPF in the setting of solid organ trans- plant immunosuppression, however, further accumulation of cases is needed to investigate this potential association. Research Letter | Dermatol Pract Concept. 2023;13(2):e2023078 3 Figure 2. (A) Perifollicular granulomatous inflammation (H&E, x200). (B) High power demonstrating numerous eosinophils in the infiltrate (H&E stain, x400). (C) Another focus with keratin remnants surrounded by granulomatous inflammation (H&E stain, x200). (D) High power demonstrating numerous eosinophils in the infiltrate (H&E stain, x400). References 1. Katoh M, Nomura T, Miyachi Y, Kabashima K. Eosinophilic pustular folliculitis: A review of the Japanese published works. J Dermatol. 2013;40(1):15-20. DOI: 10.1111/1346-8138.12008. PMID: 23083212. 2. Kim BW, Lee JH, Won CH, et al. Eosinophilic Pustular Folliculitis: Association with Long-Term Immunosuppressant Use in a Solid Organ Transplant Recipient. Ann Dermatol. 2014;26(4):520-521. DOI: 10.5021/ad.2014.26.4.520. PMID: 25143686. PMCID: PMC4135112. 3. Nakahigashi K, Doi H, Otsuka A, et al. PGD2 induces eotaxin-3 via PPARγ from sebocytes: a possible pathogenesis of eosinophilic pustular folliculitis. 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