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Sweet's syndrome, also known as Acute Febrile Neutrophilic Dermatosis, is a rare inflammatory condition. It is considered to be the prototype disease of neutrophilic dermatoses, and presents with acute onset dermal neutrophilic lesions, leukocytosis, and pyrexia. Several variants have been described both clinically and histopathologically. Classifications include . The cellular and molecular mechanisms involved in Sweet's syndrome have been difficult to elucidate due to the large variety of conditions leading to a common clinical presentation. The exact pathogenesis of Sweet's syndrome is unclear; however, new discoveries have shed light on the role of inflammatory signaling, disease induction, and relationship with malignancy. These findings include an improved understanding of inflammasome activation, malignant transformation into dermal infiltrating neutrophils, and genetic contributions. Continued investigations into effective treatments and targeted therapy will benefit patients and improve our molecular understanding of inflammatory diseases, including Sweet's syndrome.

Pyoderma gangrenosum (PG) is a rare neutrophilic dermatosis characterized by chronic, painful ulcerations. Despite increasing evidence suggesting immunological dysregulation, the role of IL-36 cytokines in PG remains poorly defined. To evaluate serum levels of IL-36α, IL-36β, IL-36γ, IL-36Ra, IL-37, and IL-38 in PG patients compared to healthy controls, and to assess their correlation with selected clinical parameters and cytokine ratios. 44 PG patients and 40 healthy controls were included in this case–control study. Serum cytokine levels were measured using ELISA. Correlations between cytokine levels and clinical features were analyzed using nonparametric tests. PG patients showed significantly lower serum levels of IL-36α and IL-36γ (p = 0.0003 and p = 0.02, respectively), with no difference in IL-36β. Conversely, levels of IL-36Ra, IL-37, and IL-38 were significantly higher in PG patients (p < 0.0001 for all). In the PG group, significant positive correlations were observed between IL-36α and IL-36β, and between IL-36β and IL-36γ, while IL-37 correlated negatively with IL-38. IL-36α was inversely associated with serum IgA levels and total ulcer surface area, and IL-36γ correlated negatively with white blood cell count. Our findings reveal a dysregulated IL-36 cytokine profile in pyoderma gangrenosum, marked by reduced serum levels of IL-36α and IL-36γ and elevated levels of IL-36Ra, IL-37, and IL-38. This may reflect a compensatory response to chronic inflammation. The inverse correlation between IL-36α and ulcer size suggests its potential involvement in wound healing. Despite lower serum levels of agonists, local biological activity of IL-36 cytokines may remain elevated due to tissue-level activation and consumption. These results highlight the therapeutic relevance of targeting the IL-36 pathway—particularly in treatment-resistant cases—and support further research into cytokine activity beyond serum concentration to guide novel therapeutic strategies.

The prognosis of melanoma has significantly improved since the introduction of immune checkpoint inhibitor (ICI) therapies. While ICIs are associated with a range of immune-related adverse events (irAEs), these reactions may occur early or late during treatment. Neutrophilic dermatoses, including pyoderma gangrenosum, are commonly observed in patients with systemic inflammatory disease, but have also been reported as rare cutaneous irAEs. To further characterize this rare phenomenon, we present the case of a 45-year-old patient with stage IIB cutaneous melanoma who underwent surgical resection of the primary tumor with split-thickness skin graft coverage, followed by adjuvant therapy with the PD-1 inhibitor nivolumab. During the one-year course of immunotherapy, the donor site of the graft exhibited persistent non-healing and progressive ulceration. However, it did not extend beyond the boundaries of the initial harvest site. Of note, the recipient site at the left heel healed without complications. The lesion was biopsied after completion of immunotherapy. Histopathological analysis revealed a neutrophilic dermatosis with PG-like features. The lesion showed rapid improvement upon initiation of dapsone therapy, which is in line with its action on neutrophils. This case underscores the diagnostic challenge posed by atypical cutaneous irAEs, particularly when localized and lacking systemic features. Awareness of such rare presentations is crucial to enable timely recognition and appropriate treatment.

PAPA syndrome is a rare autosomal dominant autoinflammatory disorder characterized by sterile pyogenic arthritis, pyoderma gangrenosum (PG), and severe acne, driven by PSTPIP1 mutations that enhance IL-1β production. IL-1 inhibitors—anakinra and canakinumab—have been reported in small case series, but comparative effectiveness, safety, and optimal dosing remain unclear. A systematic review of ten original case-report studies (19 patients) was performed, following PRISMA guidelines. Data extracted included clinical manifestations, treatment regimens, therapeutic responses across arthritis, PG, and acne, and adverse events. Complete resolution of pyogenic arthritis occurred in 11/17 treatment courses, versus 3/11 for PG and 4/10 for acne. Partial improvements were noted in 2 arthritis, 4 PG, and 1 acne cases; non-responses were most frequent in PG (4/11) and acne (5/10). Canakinumab demonstrated improved patient compliance due to its less frequent dosing schedule (every 4–8 weeks), in contrast to daily injections of anakinra. This also correlated with a trend toward fewer injection-site reactions. Reported adverse events were primarily mild, including local reactions and occasional infections. Anti-IL-1 therapy appears most effective for arthritis manifestations in PAPA syndrome, with markedly lower efficacy for PG and acne. Canakinumab’s dosing schedule offers practical advantages and potentially fewer adverse effects, but existing evidence is limited to case reports and small series. Well-designed randomized controlled trials are urgently needed to confirm efficacy, safety, and comparative benefits of anakinra versus canakinumab. Future studies should also explore genotype–phenotype correlations and extend investigation to adjunctive pathways to improve cutaneous outcomes.

Bruton’s tyrosine kinase (BTK) inhibitors have revolutionized the treatment landscape for patients with indolent lymphoid malignancies such as chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL). The most common adverse events include cardiac arrhythmia, bleeding, infection, diarrhea, arthralgias, hypertension, and skin changes. Second-generation BTK inhibitors, e.g., acalabrutinib and zanubrutinib and the non-covalent BTK inhibitor pirtobrutinib, are less toxic than the first-generation BTK inhibitor ibrutinib. The most common toxic skin symptoms related to BTKi treatment include hemorrhage, bleeding events, bruising, skin ecchymoses, and contusion; they are particularly common in patients treated with ibrutinib. Other dermatologic symptoms include rash, cellulitis, skin infections, subcutaneous abscesses and peripheral edema. This article discusses the development of skin symptoms in patients with ibrutinib and newer BTK inhibitors, and summarizes their clinical and pathological characteristics. A literature search was performed using PubMed, Web of Science, and Google Scholar for articles published in English. Additional relevant publications were obtained by reviewing the references from the chosen articles.

Sweet syndrome is an uncommon neutrophilic dermatosis in the pediatric population. As in adults, it is frequently associated with underlying conditions, including infectious diseases, neoplasias, inflammatory bowel disease, and autoimmune or autoinflammatory disorders. Genetic causes, such as chronic atypical neutrophilic dermatosis with lipodystrophy and elevated temperature syndrome, should also be considered, particularly in neonates. We report a case of a 5-week-old female infant with a confirmed Sweet syndrome associated with a rectovestibular fistula—an unusual association, with only three cases previously reported in the literature. To our knowledge, this is the first reported case in a non-Japanese neonate.

Skin lesions have been reported in about 10–12% of hairy cell leukemia (HCL) patients. Most are etiologically related to autoimmune or infectious processes, although secondary cutaneous neoplasms and drug-induced lesions are also reported. However, leukemia cutis with the direct infiltration of the skin by leukemic cells is extremely rare in HCL patients. This paper reviews the epidemiology, pathogenesis, clinical symptoms, diagnosis, and approach to treating skin lesions in HCL. A literature review of the MEDLINE database for articles in English concerning hairy cell leukemia, skin lesions, leukemia cutis, adverse events, infectious, cutaneous, drug reactions, neutrophilic dermatoses, secondary neoplasms, and vasculitis was conducted via PubMed. Publications from January 1980 to September 2020 were scrutinized. Additional relevant publications were obtained by reviewing the references from the chosen articles.

Pyoderma gangrenosum (PG) is a rare neutrophilic dermatosis strongly associated with inflammatory bowel disease (IBD). This narrative review summarizes current knowledge on the epidemiology, clinical features, proposed mechanisms, and treatment of PG in patients with IBD. In addition to population-based, large cohort, and mechanistic studies, we reviewed 115 published case reports and case series describing patients with PG and IBD and synthesized demographic, clinical, and therapeutic trends. Most patients developed PG after an IBD diagnosis, with smaller proportions presenting simultaneously or before an IBD diagnosis. PG in IBD patients typically affects middle-aged adults and has a female predominance. Clinical features are heterogeneous, which complicates recognition and timely diagnosis. Treatment responses are also highly variable. Corticosteroids and immunosuppressants are commonly used as first-line therapies, but many patients require sequential or combined regimens. Biologics are increasingly used, reflecting efforts to target shared inflammatory pathways between PG and IBD; however, treatment approaches remain highly individualized. Mechanistic and genetic studies implicate Th17/Th1 immune dysregulation, IL-1β/IL-36 signaling, and gut-skin immune crosstalk. There is a critical need for longitudinal, controlled studies to clarify pathogenesis, predict outcomes, and guide evidence-based, standardized treatment approaches in this complex patient population.

Adsorptive granulocyte and monocyte apheresis (GMA) is an extracorporeal treatment that selectively removes activated myeloid lineage leukocytes from peripheral blood. This technique consists of a column with cellulose acetate beads as absorptive leukocytapheresis carriers, and was initially used to treat ulcerative colitis. A literature search was conducted to extract recently published studies about the clinical efficacy of GMA in patients with different skin disorders, reporting information on demographics, clinical symptoms, treatment and clinical course. Dermatological diseases, in which GMA has been performed, include generalized pustular psoriasis, pyoderma gangrenosum, palmoplantar pustular psoriasis, Behcet's disease, Sweet's syndrome, adult-onset Still's disease, impetigo herpetiformis, reactive arthritis, acne and hidradenitis suppurativa syndrome, cutaneous allergic vasculitis and systemic lupus erythematosus. In most patients, GMA was started after the failure of conventional therapeutic options and it was helpful in the majority of cases. Based on the information summarized, GMA could be considered a valid non-pharmacological treatment option for patients with several dermatological conditions, which are difficult to treat with other pharmacological preparations.