Anti-citrullinated protein autoantibodies (ACPA) are diagnostic for rheumatoid arthritis (RA). The antigens recognized by these autoantibodies are produced by protein arginine deiminases (PADs), particularly PAD4. However, it remains unknown why and how PAD4 causes this aberrant citrullination in RA. Here, we report that poly-perforin pores are present on freshly isolated neutrophils from RA patients, but not on healthy donor neutrophils. Neutrophils with perforin pores also contained intracellular citrullinated proteins in the region adjacent to the pores. This response was replicated in vitro by treating neutrophils with purified perforin, which generated intense dots of anti-perforin immunofluorescence, calcium influx, and intracellular citrullination. Extensive neutrophil killing in Felty\'s syndrome, an aggressive form of RA, correlated with particularly high ACPA, and PAD4 autoantibodies. In contrast, other forms of death, including NETosis, apoptosis, and pyroptosis, produced minimal citrullination. We conclude that neutrophil targeting by perforin leading to intracellular citrullination takes place in patients with RA.

Autoimmune diseases can result in additional symptoms and complications impacting various organ systems beyond the joints. These can affect the eyes, skin, respiratory, cardiac, and renal systems. Recognizing and understanding these diverse manifestations, such as the severe eye issues seen in rheumatoid arthritis (RA) and the potentially life-threatening Felty syndrome, is crucial for clinicians to promptly identify and treat these conditions effectively. In this case presentation, we report on a patient admitted for bilateral scleritis, which was found to be secondary to multiple autoimmune syndrome type 3. During the patient\'s hospital stay, Felty syndrome was incidentally diagnosed due to the observed combination of RA, splenomegaly, and absolute neutropenia. Prompt recognition of this condition allowed the patient to receive appropriate care, including oral steroids, hydroxychloroquine, and methotrexate, decreasing the risk of severe complications.

Neutrophilic dermatosis of the dorsal hands (NDDH) is a variant of Sweet syndrome that presents with erythematous bullae, papules/plaques, or pustules on the dorsal hands. It is most commonly associated with hematologic and solid organ malignancies, though cases of NDDH associated with inflammatory bowel disease, rheumatologic disorders, and medication exposure have also been described in the literature. Felty syndrome is a rare complication of long-standing rheumatoid arthritis characterized by neuropathy, splenomegaly, and neutropenia. Granulocyte colony stimulating factors (e.g., filgrastim) can be utilized to rescue the neutropenia observed in Felty syndrome, but this treatment may subsequently cause Sweet syndrome. Herein, we present a 64-year-old man with Felty syndrome and a complex medical history who presented with sudden onset, painful blisters located on the dorsal and palmar aspects of his bilateral hands. Given the patient\'s past medical history, a broad differential diagnosis, including disseminated fungal and viral infection was initially considered. A punch biopsy of the skin lesion disclosed neutrophilic dermatosis, which together with laboratory data satisfied the von den Driesch criteria for Sweet syndrome. As the lesions were localized exclusively on the patient\'s hands, the qualification of NDDH was also endorsed.

Felty\'s syndrome was first described in 1924 by the US-American physician Augustus Roi Felty as a triad of rheumatoid arthritis, splenomegaly and leucopenia. Even nearly 100 years later, this rare syndrome is still paralleled by diagnostic and therapeutic challenges and its pathogenesis is incompletely understood. Neutropenia with potentially life-threatening infections is the main problem and several pathomechanisms like Fas-mediated apoptosis, anti-neutrophil antibodies, anti-G-CSF antibodies, neutrophil consumption in the context of NETosis and suppression of granulopoiesis by T-LGLs have been suggested. Felty\'s syndrome has various differential diagnoses as splenomegaly and cytopenia are common features of different infectious diseases, malignancies and autoimmune disorders. Additionally, benign clonal T-/NK-LGL lymphocytosis is increasingly noticed in Felty\'s syndrome, which further complicates diagnosis. Today\'s treatment options are still sparse and are largely based on case reports and small case series. Methotrexate is the mainstay of therapy, followed by rituximab, but there is less evidence for alternatives in the case of adverse reactions or failure of these drugs. This article gives an updated review about Felty\'s syndrome including its pathogenesis and treatment options.

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OBJECTIVE: Neutropenia is a key presentation of Felty syndrome (FS) and rheumatoid arthritis (RA)-associated T-cell large granular lymphocytic (T-LGL) leukaemia. Clonal rearrangement of T-cell receptor (TCR) gene supports the diagnosis of T-LGL leukaemia but not FS. Mutations in the signal transducer and activator of transcription 3 (STAT3) gene are highly specific for T-LGL leukaemia, but their prevalence in FS remains poorly clarified.
METHODS: The study included 100 patients with RA and unexplained neutropenia. TCR rearrangements were examined in blood (100 cases), bone marrow (47 cases), and spleen (12 cases) using the BIOMED-2 protocol. Patients were stratified into RA-associated T-LGL leukaemia cohort if a clonal TCR rearrangement was identified in any of the tested patient samples, and into FS cohort in other cases. Mutations in the STAT3 were examined using next-generation sequencing (NGS) technology in blood (100 cases), bone marrow (37 cases), and spleen (7 cases).
RESULTS: STAT3 mutations were identified in 71% (49/69) patients with RA-associated T-LGL leukaemia and in 10% (3/31) patients with FS (p=4.7×10-8). Three samples from the RA-associated T-LGL leukaemia cohort and 5 samples from the FS cohort had STAT3 mutations in the absence of clonal TCR rearrangement.
CONCLUSIONS: The results suggest that STAT3 mutations are significantly less common in FS than in RA-associated T-LGL leukaemia. Moreover, NGS can detect clones undetectable by fragment analysis. We speculate that in patients with RA and neutropenia, the detection of STAT3 mutations can point to T-LGL leukaemia even in the absence of clonal TCR rearrangement.

Advanced rheumatoid arthritis (RA) is complicated by extra-articular manifestations such as small- and medium-sized vasculitis, pulmonary fibrosis, and pleurisy. The clinical course of the disease is refractory and critical. Treating advanced RA with multiple extra-articular manifestations is challenging. Here, we report a case of advanced RA in a 75-year-old man with exudative pleurisy and Felty syndrome. Treatment should be initiated promptly while paying attention to the possibility of infection as a differential diagnosis of exudative pleurisy because of the drastic change in the patient\'s condition due to disease progression. In addition, appropriate treatment is required to differentiate between Felty syndrome and malignant diseases. In older patients with RV complicated by pleurisy and Felty syndrome, starting steroids and immunosuppressive agents is crucial when conducting a thorough examination and considering the rapid progression of symptoms.

BACKGROUND: Felty syndrome is defined by three conditions: neutropenia, rheumatoid arthritis, and splenomegaly. Neutropenia associated with pancytopenia may further affect the dental condition of a patient. Periodontal treatment and surgery in patients with Felty syndrome necessitates cooperation with a hematologist. Here we present a case of a patient with Felty syndrome who was initially referred to the oral surgery hospital attached to the School of Dentistry for extensive periodontitis. She was effectively treated in collaboration with the hematology department.
METHODS: A 55-year-old Asian woman visited our department with concerns of worsening tooth mobility, discomfort, and spontaneous gingival bleeding. Initial periodontal examination revealed generalized severe periodontitis (Stage IV Grade C) resulting from leukopenia/neutropenia and poor oral hygiene. A thorough treatment strategy involving comprehensive dental procedures, such as multiple extractions and extensive prosthetic treatment, was implemented. Following the diagnosis of Felty syndrome, the patient was started on treatment with oral prednisolone 40 mg/day, which effectively controlled the disease. Furthermore, there was no recurrence of severe periodontitis after the periodontal treatment.
CONCLUSIONS: Dentists and physicians should be aware that immunocompromised individuals with pancytopenia and poor oral hygiene are at risk of developing extensive periodontitis. If their susceptibility to infection and pancytopenia-related bleeding can be managed, such patients can still receive comprehensive dental treatment, including teeth extractions and periodontal therapy. Cooperation among the dentist, hematologist, and patient is necessary to improve treatment outcomes and the patient\'s quality of life.

T cell large granular lymphocyte leukemia (T-LGLL) is an interesting case at the intersection of autoimmunity and cancer. In T-LGLL, T cells with somatic pathogenic mutations (mainly in STAT3) are linked to rheumatoid arthritis (RA) and neutropenia. A rare subtype of RA, Felty\'s syndrome, exhibits overlapping clinical features and comparable frequencies of activating STAT3 mutations in T cells as T-LGLL, which hints at a potential T-LGLL-Felty\'s syndrome-RA axis. Somatic mutations could shed light on the unexplained pathologies of these disorders. However, the causality of somatic mutations-do somatic mutations in immune cells cause inflammation, or does prolonged inflammation predispose to mutagenesis-remains unanswered. This review will focus on the recent advances in understanding somatic mutations in T-LGLL and related autoimmune conditions as a master regulatory network that sustains lymphoproliferation and inflammation.

Felty syndrome (FS) is a disorder that develops after a long history of erosive rheumatoid arthritis and presents with splenomegaly and neutropenia. In addition to joint deformities, FS causes a variety of extra-articular manifestations such as vasculitis, skin lesions, and lymphadenopathy. FS is also reported to cause non-cirrhotic portal hypertension which may result in variceal bleeding. FS is usually treated by disease-modifying anti-rheumatic drugs (DMARDs) such as methotrexate. Herein, we report a case of rapidly deteriorating FS and a severe relapsing neutropenia only a few weeks after discontinuation of methotrexate and other available DMARDs. The patient presented with a fever and a multi-drug resistant gangrenous ulcer consistent with ecthyma gangrenosum. The patient was also found to have hepatosplenomegaly and portal hypertension. The case was managed with antibiotics and symptomatic treatments only as DMARDs were either unavailable or not affordable by the patient. However, the patient\'s condition did not improve. This case highlights that DMARDs are considered an essential part of preventing infections due to FS neutropenia. Patients with FS should continue DMARDs for life to avoid the relapse of their condition.