Kikuchi-Fujimoto Disease Preceding Overlap Syndrome of Sjögren's Syndrome and Systemic Lupus Erythematosus: Literature Review Based on a Case Report.

Kikuchi-Fujimoto disease (KFD) is a benign, self-limiting histiocytic necrotizing lymphadenitis systemic disorder with unknown etiology. KFD has been known for half a century, but difficulties in distinguishing it remain. Its diagnostic significance is related to the increasing prevalence of KFD with autoimmune diseases in various timeframes. Systemic lupus erythematosus (SLE) is the most prevalent autoimmune connective tissue disease (AICTD) appearing alongside KFD. An 18-year-old female presented with acute muscle weakness, shortness of breath, fever, and significant weight loss for 5 months before admission. Pain and morning joint stiffness had been felt for 9 months. One year ago, she lumped her right neck and was diagnosed with KFD from the excision biopsy and immunohistochemical staining (CD68). Creatine-kinase enzymes and C-Reactive protein were elevated with a high anti-Ku and anti-Jo-1 negative level. There was a low level of complements, high anti-nuclear antibody titer, with positive anti-SS-A. Sialometry and Schirmer test showed reduced salivary and lacrimal gland production. We diagnosed this patient as having an overlap syndrome preceded by KFD. The AICTD involved was Sjögren's syndrome and SLE. Although KFD is considered a self-limiting disease, its occurrence should be noticed regarding the possibility of other autoimmune conditions. KFD usually coincides with AICTD, although it could also precede or occur afterward. This case is reported to raise awareness of the overlap syndrome preceded by KFD.

Pathogenic role and diagnostic utility of interferon-α in histiocytic necrotizing lymphadenitis.

PURPOSE: Histiocytic necrotizing lymphadenitis (HNL) is an inflammatory disease of unknown etiology clinically characterized by painful lymphadenopathy. This study aimed to investigate the role of interferon (IFN)-α in the pathogenesis of HNL and the clinical significance of serum IFN-α levels for the diagnosis and monitoring of HNL disease activity. METHODS: This study enrolled 47 patients with HNL and 43 patients with other inflammatory diseases that require HNL differentiation including malignant lymphoma (ML), bacterial lymphadenitis, and Kawasaki disease. Expression of IFN-stimulated genes (ISGs) and MX1 in the lymph nodes was measured by real-time quantitative reverse transcription polymerase chain reaction and immunofluorescence staining, respectively. Enzyme-linked immunosorbent assay was used to quantify serum cytokine levels. The results were compared with the clinical features and disease course of HNL. RESULTS: Patients with HNL had a significantly elevated ISG expression in the lymph nodes compared with those with ML. MX1 and CD123, a specific marker of plasmacytoid dendritic cells (pDCs), were colocalized. In patients with HNL, serum IFN-α levels were significantly elevated and positively correlated with disease activity. The serum IFN-α level cutoff value for differentiating HNL from other diseases was 11.5 pg/mL. CONCLUSION: IFN-α overproduction from pDCs may play a critical role in HNL pathogenesis. The serum IFN-α level may be a valuable biomarker for the diagnosis and monitoring of disease activity in patients with HNL.

Clinical features and recurrence predictors of histiocytic necrotizing lymphadenitis in Chinese children.

OBJECTIVES: To characterize the clinical features and to identify the predictors of recurrence of histiocytic necrotizing lymphadenitis (HNL) in Chinese children. STUDY DESIGN: This study retrospectively analyzed the clinical characteristics, laboratory and pathological findings, and recurrence status of children diagnosed with HNL at a single center in China from January 2018 to May 2023. Logistic regression analysis was employed to identify predictors of HNL recurrence. RESULTS: 181 Chinese children with histopathologically confirmed HNL were enrolled (121 males and 60 females). The mean age was 9.3 ± 2.9 years. The most prominent clinical features were fever (98.9%) and cervical lymphadenopathy (98.3%). Aseptic meningitis was the most frequent complication (38.5%), while hemophagocytic lymphohistiocytosis and autoimmune disease were rare (1.7% and 1.2%, respectively). Recurrence occurred in 12.7% of patients. Erythrocyte sedimentation rate (> 30 mm/h) was the significant predictors of HNL recurrence, with odds ratios of 6.107, respectively. CONCLUSION: Our study demonstrates that fever and cervical lymphadenopathy are the most frequent clinical manifestations of HNL in Chinese children, which often coexist with aseptic meningitis. HNL patients with risk factors require follow-up for recurrence.

[Clinical characteristics and treatment in adults and children with histiocytic necroti-zing lymphadenitis].

OBJECTIVE: To analyze the clinical data of histiocytic necrotizing lymphadenitis(HNL), comparing the similarities and differences between children and adults, to deepen the understanding of the disease by clinical physicians, and to improve diagnostic rate and reduce misdiagnosis and mistreatment. METHODS: The clinical data of hospitalized patients with histiocytic necrotizing lymphadenitis diagnosed by biopsy from January 2010 to August 2023 in Peking University First Hospital were collec-ted, and the clinical features, laboratory examinations, pathological features, treatments with antibiotics and glucocorticoids, and prognosis of histiocytic necrotic lymphadenitis were analyzed. Grouped based on age, the differences of clinical characteristics, laboratory tests, treatment, and prognosis between the children group (< 16 years old) and the adult group (≥16 years old) were compared. RESULTS: Among the 81 enrolled patients, there were 42 males and 39 females. The median age was 21(14, 29) years, the median duration of disease was 20.0(13.0, 30.0) days, and the median length of hospital stay was 13.0 (10.0, 15.0) days. The first symptoms were fever, lymphadenopathy, and both. All the patients had enlarged lymph nodes with different parts and sizes, 96.3% (78 of 81) of the patients had cervical lymphadenopathy, 50.6% (41 of 81) had bilateral cervical lymphadenopathy, 55.6% (45 of 81) had supraclavicular, axillary or inguinal lymphadenopathy, and the median lymph node diameter was 20.0(20.0, 30.0) mm. Only one patient had no fever, the other 80 patients had fever, the median peak body temperature was 39.0(38.0, 39.8) ℃. Accompanying symptoms: rash (8.6%, 7/81), fatigue (34.6%, 28/81), night sweating (8.6%, 7/81), chills (25.3%, 25/81), muscle soreness (13.6%, 11/81), and joint pain (6.2%, 5/81). There were 17 cases (21.0%, 17/81) of hepatosplenomegaly, of which 12 cases (70.6%, 12/17) were splenomegaly. 68.8%(55/80) of patients had a decrease in white blood cell (WBC) count, with 47.5%(38/80)increased in lymphocyte(LY)proportion, 53.4%(39/73) increased in high-sensitivity C-reactive protein(CRP), 79.2%(57/72) increased in erythrocyte sedimentation rate(ESR), 22.2%(18/81) increased in alanine transaminase(ALT), 27.2%(22/81) elevated in aspartate transaminase(AST), and 81.6%(62/76) elevated in lactate dehydrogenase(LDH). All the 81 patients underwent lymph node biopsy, and 77.8%(63/81) of the patients showed that most of the structures in the lymph nodes were destroyed or disappeared, and 16.0%(13/81) of the lymph nodes were still in existence, hyperplasia and normal lymph node were 1.2%(1/81) respectively, and 3.7%(3/81) had normal lymph node structures. Immunohistochemical staining was performed in 67 cases. The percentages of CD3+ and CD68(KP1)+ were respectively 97.0%(65/67), and MPO+ were 94.0%(63/67). In the study, 51 patients (63.0%, 51/81) were treated with glucocorticoid therapy after diagnosis. The median time for temperature to return to normal was 1.0(1.0, 4.0) days after glucocorticoid therapy. when the glucocorticoid treatment worked best, the body temperature could drop to normal on the same day. There were significant differences in length of stay, predisposing factors, chills, the rate of increase in high-sensitivity CRP, antibiotic and glucocorticoid treatment between the adults and children groups (P < 0.05). CONCLUSION: In clinical practice, if there are cases with unexplained fever, superficial lymph node enlargement, and reduced white blood cells as clinical characteristics, and general antibiotics treatment is ineffective, histiocytic necrotic lymphadenitis should be considered. Lymph node biopsy should be performed as early as possible to clarify the diagnosis, reduce misdiagnosis and mistreatment, and symptomatic treatment should be the main treatment. Glucocorticoids therapy has a definite therapeutic effect.

Kikuchi disease complicated with aseptic meningitis following COVID-19 Vaccination: a case report.

BACKGROUND: Kikuchi Fujimoto disease is a rare self-limiting disorder mainly affecting young Asian females. The typical presentation is unexplained fever with associated cervical lymphadenopathy. It can mimic many sinister diseases such as lymphoma, tuberculosis, and systemic lupus erythematosus. Aseptic meningitis due to Kikuchi disease is extremely rare, and majority were reported from Japan. There have been no published cases of aseptic meningitis due to Kikuchi disease in Sri Lanka. CASE PRESENTATION: A 29 years old Sri Lankan female presented with a prolonged fever for three weeks with an associated headache for five days duration. She developed painful cervical lymphadenopathy during the hospital stay. She has been previously well and had been vaccinated against COVID-19 six weeks before. Her lumbar puncture showed lymphocytic pleocytosis with marginally elevated protein levels and reduced ratio of serum to CSF sugar. Lymph node biopsy was consistent with necrotizing lymphadenitis. She was subsequently diagnosed with Kikuchi disease complicated with aseptic meningitis. She responded to corticosteroids well and had an uneventful recovery. CONCLUSION: Kikuchi disease is a rare self-limiting disorder that can be complicated with aseptic meningitis on infrequent occasions. Other conditions such as tuberculosis, lymphoma, systemic lupus erythematosus, and adult-onset Still's disease should be considered as differential diagnoses. Knowledge of Kikuchi disease and its complications will prevent unnecessary investigations which delay the early diagnosis and treatment.

Kikuchi-Fujimoto disease, simultaneously diagnosed with systemic lupus erythematosus in an Arabic female: an agonizing combination.

Kikuchi-Fujimoto disease (KFD), also known as histiocytic necrotizing lymphadenitis, is a rare, benign condition affecting young Oriental-Asian females. It is characterized by fever and tender cervical lymphadenopathy with an unclear aetiology, and in most longitudinal reviews, KFD occurs before systemic lupus erythematosus (SLE). Herein, the case of a 28-year-old Kuwaiti female without any relevant past medical history, who was simultaneously diagnosed with KFD and SLE following an Ebstein-Barr virus infection, is reported. The patient was treated with oral prednisolone, hydroxychloroquine, cyclosporin, and belimumab and her response was clinically and biochemically favourable. Although KFD is prevalent in Asian populations, it may affect all races. Early diagnosis of KFD is difficult, particularly when simultaneously diagnosed with SLE, but crucial to preventing inappropriate therapy. Clinicians need to know about this rare disease, especially when patients present with fever and swollen lymph nodes, due to a risk of misdiagnosis with tuberculosis or lymphoma, as these are more often thought to be the cause of such symptoms.

Distinguishing Kikuchi-Fujimoto disease from lymphoma in patients by clinical and PET/CT features.

To develop a scheme for distinguishing Kikuchi-Fujimoto disease (KFD) from lymphoma in patients presenting enlarged lymph nodes (LNs) predominantly on the upper side of the diaphragm. From November 2015 to August 2023, 32 KFD patients and 38 lymphoma patients were pathologically confirmed and enrolled in this retrospectively study. Clinical and 18F-fluorodeoxyglucose positron emission tomography (PET)/computed tomography (CT) features were collected. When comparing those PET/CT parameters, we set 5 models with different research objects: (1) all affected LNs; (2) the 5 largest affected LNs in terms of maximum diameter; (3) the 5 largest affected LNs in terms of maximum standard uptake values (SUVmax); (4) the largest affected LNs in terms of maximum diameter; (5) the largest affected LNs in terms of SUVmax. Compared to lymphoma patients, KFD patients were younger; and with higher incidence of fever, arthralgia, abnormal serum white blood cell, lactate dehydrogenase (LDH) and splenomegaly; lower incidence of affected LNs perinodal infiltration, necrosis and conglomeration; more affected LNs in Head and Neck nodes (particularly in level II) and Axillary in KFD (P ˂ .05). PET/CT parameters presented as various difference in each model. Finally, 11 clinical and PET/CT features (age ≤ 34, with fever, arthralgia, abnormal white blood cell, abnormal LDH, and without node necrosis and node conglomeration have a score of 2 each; splenomegaly, perinodal infiltration, median maximum diameter ≤ 20.5 and median SUVmax ≤ 7.1 of affected LNs in model 2 have score of 1 each) were selected as scheme items for distinguishing KFD from lymphoma. Individuals who have a total score > 8, meet the criteria for KFD. Sensitivity and specificity were high: 86.8% (95% CI: 71.9%, 95.5%) and 96.9% (95% CI: 83.7%, 99.5%), AUC = 0.975 (95% CI: 90.5%, 99.6%), respectively. It can effectively distinguish KFD from lymphoma by clinical and PET/CT parameters.

Kikuchi-Fujimoto Disease: A Case Report of Prolonged Fever and Lymphadenopathy in a Young Girl.

Kikuchi-Fujimoto disease (KFD) is a benign and self-limited disorder that usually presents with regional cervical lymphadenopathy and fever. We report a case of a 12-year-old female who complained of fever, night sweating, significant weight loss, and tender right cervical lymph node enlargement for 2 months. A full workup including laboratory tests and imaging studies, an excisional biopsy, and histopathological analysis were done, and the diagnosis of KFD was confirmed. The patient was treated with analgesia and oral prednisolone, resulting in good improvement. A high degree of clinical suspicion is imperative for physicians, given the rarity of the disease and the associated diagnostic challenges.

Kikuchi-Fujimoto disease associated with a flare-up of a leukocytoclastic vasculitis: A rare case report and review of literature.

RATIONALE: Kikuchi-Fujimoto disease (KFD) also known as histiocytic necrotizing lymphadenopathy is an exceedingly rare cause of cervical lymphadenopathy, commonly accompanied by systemic symptoms such as fever, fatigue, night sweats, myalgia, skin rash. PATIENT CONCERNS: In this paper, we report the case of a 22-year-old female patient who experienced a flare-up of leukocytoclastic vasculitis that was complicated by the appearance of a cervical lymph node with dysphagia, fever and nausea. DIAGNOSIS: Infectious and autoimmune workup came back negative. INTERVENTIONS: Excisional lymph node biopsy was done and the pathology results were consistent with histiocytic necrotizing lymphadenitis in keeping with Kikuchi-Fujimoto disease. OUTCOMES: Patient improved on intravenous corticosteroids and was discharged on per os prednisone. Six month follow-up shows complete resolution of her symptoms. LESSONS: KFD should be ruled out in patients with autoimmune or inflammatory diseases who develop lymphadenopathies.

Kikuchi-Fujimoto disease during early pregnancy.

Kikuchi-Fujimoto disease (KFD) is rare during pregnancy. It is characterized by necrotizing lymphadenitis and often occurs in young Asian women. We report a case of KFD during pregnancy, which was difficult to diagnose. A 37-year-old pregnant female (gestational week [GW] 7+5) was admitted to our hospital because of hyperemesis gravidarum. On the eighth day of hospitalization (GW 8+6), she suddenly developed a fever (38.0°C) with skin rash and posterior pharynx redness. Blood tests showed pancytopenia and abnormal liver function. The patient was misdiagnosed with severe Epstein-Barr virus infection and administered with prednisolone. Subsequently, cervical lymphadenopathy was observed, and biopsy results led to the diagnosis of KFD. Thereafter, her symptoms improved, and she was discharged at GW 13+4. KFD must be included as a differential diagnosis for patients with fever, abnormal liver function, and pancytopenia during pregnancy.

[Recurrent lymphadenitis was Kikuchi-Fujimoto disease]. / Lymfadenit som mystiskt återkom var Kikuchi­Fujimotos sjukdom.

Kikuchi-Fujimoto disease, or histiocytic necrotizing lymphadenitis, is in most cases a benign disease which affects lymph nodes in the cervical region. Cervical adenopathy and fever are the most common symptoms, and young adults are mostly affected. Lymph node biopsy is the mode of diagnosis with demonstration of paracortical areas of apoptotic necrosis with abundant karyorrhectic debris and a proliferation of histiocytes, plasmacytoid dendritic cells, and CD8+ T cells in the absence of neutrophils. In most cases, the disease is self-limiting but it can be recurrent or evolve to SLE. Treatment varies from symptomatic to more systemic with cortisone and intravenous immunoglobulin.

Histiocytic necrotizing lymphadenitis with hemophagocytic lymphohistiocytosis in adults: A single-center analysis of 5 cases.

BACKGROUND: Histiocytic necrotizing lymphadenitis (HNL) is a self-limited inflammatory disease of unknown pathogenesis. A very small fraction of patients with HNL could develop hemophagocytic lymphohistiocytosis (HLH), a hyperinflammatory disorder. These patients are diagnosed as HNL with HLH (HNL-HLH). HNL-HLH in the pediatric population has been systemically studied, however, the clinical, laboratory, and radiological features and outcomes of adult patients with HNL-HLH remain to be explored. We aimed to explore the clinical, laboratory, and radiological features and outcomes of adult patients with HNL-HLH. METHODS: We collected the clinical data of patients with HNL-HLH admitted to the First Affiliated Hospital of Nanjing Medical University from October 2010 to June 2015. All the patients underwent lymph node biopsy and have a pathological diagnosis of HNL. The age, gender, clinical presentation, lymph node signs, laboratory findings and imaging data, and pathological findings of the patients were collected. RESULTS: In this study, we reported five adult patients with HNL-HLH. All five patients showed enlarged lymph nodes and prolonged fever. Laboratory findings were consistent with the diagnosis of HLH. 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) showed enlarged lymph nodes with increased FDG uptake and splenic hypermetabolism could be present. All the patients responded well to corticosteroids and had a good prognosis. Two of the five patients were diagnosed with systemic lupus erythematosus during the follow-up. CONCLUSIONS: Our study demonstrated that adult patients with HNL-HLH showed distinct clinical, laboratory, and radiological features. And the prognosis is good and patients could be managed with steroids and supportive care.

Occlusive Retinal Vasculitis in a Pediatric Patient With Kikuchi-Fujimoto Disease and Sickle Cell Trait.

A 13-year-old Black male patient with a history of Kikuchi-Fujimoto disease (KFD) and sickle cell trait presented with acute painless vision loss and no light perception vision (NLP) in his left eye. The examination was indicative of occlusive retinal vasculitis with near total central retinal artery occlusion (CRAO). He was started on oral steroids with dramatic reperfusion and improvement of the retinal hemorrhages. However, his vision remained at NLP. Oral steroids were tapered, and rituximab infusion was initiated. While ocular involvement is uncommon in KFD, vision-limiting complications, such as occlusive retinal vasculitis, ophthalmic artery occlusion, and CRAO can occur. Early systemic immunosuppression is key in achieving rapid remission. [Ophthalmic Surg Lasers Imaging Retina 2024;55:235-239.].

Kikuchi disease in acute leukaemia: a distinct clinical syndrome with HLA association.

AIMS: To report the clinicopathological features of Kikuchi disease in patients with acute leukaemia, emphasising similarities among cases. METHODS AND RESULTS: In a cohort of 454 Kikuchi disease patients, we identified three cases of concurrent acute leukaemia. These patients shared similar clinical traits, with Kikuchi disease emerging approximately a month after induction chemotherapy onset, featuring neck-region lymphadenopathy. Notably, two patients were middle-aged, deviating from the typical age distribution of Kikuchi disease. Histologically, these cases aligned with typical Kikuchi disease. Negative immunohistochemical stains (CD34, CD117, ERG, TdT) indicated the absence of extramedullary leukaemic infiltration. Herpes simplex virus immunohistochemical staining was also negative. Significantly, a human leucocyte antigen (HLA) association was observed in these three cases. HLA-B*15:01, C*04:01, and DRB1*04:06 were more prevalent in these patients compared to the general population (compared with three independent control cohorts: Taiwanese Han Chinese (n = 504), Tzu Chi Taiwanese bone marrow donors (n = 364) and Hong Kong Chinese (n = 5266)). CONCLUSIONS: Our study underscores the unique link between Kikuchi disease and acute leukaemia, characterised by specific features and HLA associations. This underlines Kikuchi disease as a possible differential diagnosis in pertinent clinical scenarios. Furthermore, this syndrome offers insights into postchemotherapy immunology in acute leukaemia, enhancing comprehension.

A rare co-existence of histiocytic necrotizing lymphadenitis with metastatic papillary thyroid carcinoma and review of the literature.

Histiocytic necrotizing lymphadenitis (HNL) is a benign, self-limiting disease that is rare clinically. The coexistence of HNL and tumor is rarer. We report a male patient who was preoperatively diagnosed with papillary thyroid carcinoma with cervical lymph nodes metastasis, and the postoperative pathological examination showed histiocytic necrotizing lymphadenitis combined with metastatic papillary thyroid carcinoma in the same single lymph node. More interestingly, Epstein‒Barr virus was positive in these lymph nodes by in situ hybridization. This may suggest a trigger for the coexistence of the two diseases.

Kikuchi-Fujimoto disease type lymph node reaction with increased plasmacytoid dendritic cells may appear as a side effect following COVID-19 vaccination: Report of a case and literature review.

Subsequent to mass vaccination programs against COVID-19, diverse side effects have been described, both at the injection site, such as pain, redness and swelling, and systemic effects such as fatigue, headache, muscle or joint pain. On rare occasions, a lymphadenopathic syndrome may develop, raising the clinical suspicion of a lymphoproliferative disorder. We present the case of a 30-year-old woman who developed self-limiting left axillary lymphadenopathy following COVID-19 vaccination. To date, only seven similar cases with a complete clinicopathological description have been published, and fourteen cases have been notified to the European adverse events databases (Eudravigilance) in relationship with vaccination against COVID-19. It is important to be aware of this potential complication when a lymphadenopathic syndrome develops following vaccination, to avoid unnecessary treatment.

Kikuchi-Fujimoto disease, a rare benign disease with atypical histomorphology: more than meets the eye.

Kikuchi-Fujimoto disease (KFD) is a benign self-limiting condition primarily affecting young females. It usually presents with fever and cervical lymphadenopathy of unknown aetiology with a preponderance of the Asian population. Histopathology is critical in making an accurate diagnosis. While the typical microscopic features include paracortical necrosis with debris, histiocytosis with immunoblasts, and absent neutrophils, rarely, KFD can show atypical features like marked immunoblastic proliferation mimicking lymphoma, demonstrate vasculitis mimicking lupus erythematosus, etc. The diagnosis is extremely challenging if such features occur in cases with generalised lymphadenopathy, which is infrequent in KFD. The study aims to describe the morphological, clinical, and immunohistochemical features of KFD and determine the frequency of the atypical features. We also analysed the subtle histological and immunohistochemical features that aid in the diagnosis of atypical cases. Cases reported as KFD over a period of 6 years were retrieved from the archives of histopathology. The morphological features were categorised as typical and atypical. In the atypical cases, the features that aided in the correct diagnosis of KFD were analysed. Out of the 42 cases evaluated, 23.9% (n=10) had generalised lymphadenopathy; 57.2% (n=24) were women with a median age of 25 years. Leukopenia was observed in 42% (n=13) of patients. Typical features were present in 76.2% (n=32) cases and 23.8% (n=10) presented with atypical features. Eight cases were antinuclear antibody-positive. Atypical features included five (50%) cases with vasculitis and panniculitis, and three (30%) cases with large, atypical cells for which immunohistochemistry (IHC) was performed. In two of these cases, the patent sinuses, absence of neutrophils, and IHC with CD68 aided the diagnosis. There is an overlap of clinical and histopathological features between KFD and malignant lymphomas and systemic lupus erythematosus. Given the fact that the atypical features (23.8%) are not rare occurrences in KFD, correlations with clinical findings and ancillary studies are essential to avoid misdiagnosis and inadvertent therapy.

Clinical features of histiocytic necrotizing lymphadenitis in children.

Due to its nonspecific clinical characteristics, histiocytic necrotizing lymphadenitis (HNL) is often misdiagnosed as a suppurative cervical lymphadenitis and lymphoma. Thus, this study aimed to investigate the clinical characteristics of HNL in pediatric patients. We retrospectively identified 61 patients with histopathologically confirmed HNL. Clinical and laboratory data, including age, sex, clinical manifestations, laboratory investigations, histological discoveries, treatment, and outcomes, were collected from the medical records to determine associations with extracervical lymph node (LN) involvement. The mean age of patients was 9.7 ± 2.8 years (range, 1.5-14.0 years), and the male-to-female ratio was 2.2:1. The most common systemic symptom was fever in all patients. The median pre-admission and total durations of fever were 13.0 (interquartile range [IQR]: 9.0-22.5 days) and 22.0 days (IQR: 17.0-33.0 days), respectively. Patients with temporary fever (< 2 weeks) had a higher peak temperature and were more likely to undergo LN biopsy after admission than those with a prolonged fever (≥ 2 weeks). Multivariate analysis revealed that peak temperature ≥ 40 °C was significantly associated with a longer fever duration (P = 0.023). Laboratory values showed leukopenia (68.9%), which presented more frequently in solitary cervical LNs than in extracervical LNs (82.4% vs. 52.9%, p = 0.027) in patients with prolonged fever. CONCLUSIONS: HNL is often misdiagnosed in older children with persistent fever and lymphadenopathy, leading to unnecessary diagnostic tests and evaluations, inappropriate antibiotic administration, and mismanagement. A multidisciplinary team, including primary care providers, rheumatologists, and pathologists, can improve patient outcomes by increasing their awareness of this rare condition. WHAT IS KNOWN: • Histiocytic necrotizing lymphadenitis (HNL) is characterized by fever, leukopenia, and neck lymphadenopathy with unknown etiology. • The lack of neutrophils or eosinophils in the histology, immunohistochemistry results help distinguish HNL from infectious causes. Although HNL is a self-limiting disease, antibiotics and steroid treatments were used inappropriately. WHAT IS NEW: • A fever peak ≥ 40 °C was associated with a longer fever duration in HNL patients. Leukopenia presented more frequently in solitary cervical lymph node (LNs) than in extracervical LNs inpatients with prolonged fever. • Steroids are not recommended as a routine treatment, however, in some severe or relapsing cases with persistent symptoms, prednisolone (5 mg twice a day for 2 days) or other steroids (an equivalent dose of prednisolone) responded favorably.

Unilateral gluteal myositis as a unique presentation in mesenteric Kikuchi-Fujimoto disease.

Kikuchi-Fujimoto disease (KFD) is a self-limiting disease, characterised by fever and cervical lymphadenopathy. Lymphadenopathy without cervical lymph node involvement is rare and may mimic lymphoma. Although KFD can be associated with extranodal involvement, muscle involvement has not been reported. Herein, we report a novel case of unilateral gluteal myositis associated with mesenteric KFD in a patient who presented with persistent fever and right hip pain. Radiological imaging revealed an inflammatory lesion on the right gluteal muscle and multiple enlarged abdominal lymph nodes. No cervical lymphadenopathy was observed. A mesenteric lymph node biopsy was performed, and the histopathological findings led to a diagnosis of KFD. By day 29, the patient's body temperature gradually returned to normal without any therapeutic intervention. Follow-up radiological imaging showed resolution of the gluteal lesion and a significant decrease in abdominal lymph node size. Considering the clinical course, the unilateral myositis may have developed as an extranodal involvement of KFD. Even if the clinical findings appear unrelated to those of KFD, a differential diagnosis that includes KFD should be considered in patients with unknown origin of fever.