Kikuchi–Fujimoto disease in the Eastern Mediterranean zone

Kikuchi–Fujimoto disease (KFD) is a rare benign and self-limiting syndrome. We aim to review cases of KFD at our institution as a rare illness in the Arab ethnic descent and to analyse reports from most countries in the East Mediterranean zone. This is a retrospective study in which the histopathology database was searched for the diagnosis of KFD. A full review of KFD patients’ medical records was done. Data regarding demographic features, clinical presentation, laboratory findings, comorbidities, and management protocols were obtained. Published KFD cases from east Mediterranean countries were discussed and compared to other parts of the world. Out of 1968 lymph node biopsies studied, 11 (0.6%) cases of KFD were identified. The mean age of patients with KFD was 32 years (4–59). 73% (8/11) were females. The disease was self-limiting in 5 patients (45%); corticosteroid therapy was needed in 4 patients (34%). One patient was treated with methotrexate and one with antibiotics. One patient died as a consequence of lymphoma. Jordanians and Mediterranean populations, especially those of Arab ethnic background, seem to have low rates of KFD. The genetic susceptibility theory may help to explain the significantly higher disease prevalence among East Asians. Early diagnosis of KFD—although challenging—is essential to reduce the morbidity related to this illness.

www.nature.com/scientificreports/ 37 reports of KFD in the East Mediterranean zone were retrieved, with a total of 95 patients. 15 reports (60 patients) were from Arabic countries. Lymphadenopathy (in 32/37 studies) and fever (in 20/37 studies) were the main presenting symptoms, whereas fatigue and joint pain were only occasionally reported (in 4/37 and 1/37 reports, respectively). In fact, these findings apply to both Arab and non-Arab Mediterranean countries included in Table 2.
When compared to other ethnic groups, tender lymphadenitis (50%) and fever (43%) were, similarly; the most frequent clinical findings in studies from East Asia (Taiwan) and China 4,11,12 , while Joint pain and hepatosplenomegaly were much less encountered in the Asian ethnicity. Reports from western countries, which may still include up to 20% of patients from Asian backgrounds 13 , also showed that lymphadenopathy and fever represent the classic hallmarks of the disease 3 .

Discussion
In this study, we investigated the prevalence rate of KFD among Jordanian patients who underwent lymph node biopsy at our center. Our results showed that out of each thousand lymph node biopsies, 6 were diagnosed with KFD (0.6%), which is a comparable rate to others reported in non-Asian communities. www.nature.com/scientificreports/ Mediterranean populations of Arab ethnic background seem to have similar rates. Reported numbers from the gulf region might be slightly affected by non-Arab ethnicities included in the studies. In Kuwait 14 , between 2005 and 2009, a study reviewed 2,369 fine needle aspirations (FNA) of patients with lymphadenopathy. Of these, 76 (3.2%) patients were diagnosed with KFD or were suggestive of KFD, 51 of the 76 (67%) KFD patients were non-Kuwaiti, primarily from the Indian Subcontinent and South-East Asia. In Saudi Arabia, a study included 2500 lymph node biopsies, revealed KFD in only 15 (0.6%) patients 15 . Another report from Saudi Arabia by Kutty MK et al. recognized only 5 cases of KFD in 920 lymph node biopsies (0.5%) 16 .
A-14-patient case series from Qatar by Al Soub et al. 17 , represented a KFD incidence rate of approximately 1.6% from 900 lymph node biopsies; Almost half (43%) of KFD cases in this series were of non-Qatari nationalities.
Similarly, large data from other Mediterranean ethnicities such as Turki 4 , Iranian 18 , and Greek 19 , are still lacking. The published small-volume reports may indicate low incidence rate. In addition, review of these reports revealed clinical characteristics that correspond with data from other Mediterranean populations. Table 2 summarizes the main reports of KFD from Eastern Mediterranean countries. www.nature.com/scientificreports/ Studies from Asia disclosed 10-40 times higher incidence rates of KFD, especially among female patients with cervical lymphadenopathy, which seemed to be the main presenting sign. In a retrospective study of 147 Korean patients who had enlarged (≥ 1 cm in diameter) cervical lymph nodes for a duration > 1 week, 51 (34.7%) had KFD. All patients in this study had core needle biopsies obtained under ultrasound guidance 11 . In their analysis of published literature, Kucukardali and colleagues showed that nearly 50% (166/330) of reported KFD cases between 1991 and 2005 originated in East Asia and the Far-East, with about 36% being from Taiwan, which had the majority of reported cases 4 .
There is no clear explanation for the lower incidence of KFD among Arab and other non-Asian ethnicities. However, some studies raised the theory of genetic susceptibility that makes east-Asians at higher risk to become affected. In one study by Tanaka and colleagues 20 , they performed DNA typing of human leukocyte antigens (HLA) class II genes (HLA-DR, -DQ, and -DP), and found that frequencies of DPA1*01 and DPB1*0202 allele in HLA class II genes were significantly higher among KFD patients; this allele is relatively frequent in Asians (e.g., Korean 9.9%, Japanese 4.5%) when compared to Caucasians (e.g., French 0.4%, Italian 0.8%), and Arabs (Lebanese 2.97% 21 ) 22,23 . It is also unclear if environmental triggers play a role in the pathogenesis of this illness.
Although KFD is considered a benign condition, the significant morbidity with frequent hospitalization may be attributed to mistaken diagnosis with other lymphoproliferative disorders, connective tissue diseases or infectious etiologies. Multiple other factors may also contribute to the increased morbidity of KFD; these include either disease-linked complications or concurrent other systemic illnesses. Complications that have been described varied from potentially fatal manifestations, such as disseminated intravascular coagulopathy (DIC) 24,25 , abrupt heart failure, KFD-triggered hemaphagocytic syndrome, and polymyositis with respiratory failure [26][27][28] , to less extensive and regional implications similar to lymphedema and cutaneous eruption 29,30 . Moreover, some reports described the occurrence of other conditions simultaneously with KFD, such as Hashimoto thyroiditis 31,32 , aseptic meningitis (only 4 cases reported) 33,34 and Still's disease 35 ; these may contribute to the increased morbidity of the disease.
The diagnosis of KFD is challenging. It relies on a combination of clinical and histopathologic features. Histologically, the disease is evaluating in different stages represented by three subtypes; the early proliferative type, the necrotizing type and the xanthomatous type. The necrotizing type is the most common and characterized by the presence of non-neutrophilic necrotizing foci surrounded by mononuclear cells and show abundant karyorrhectic debris. The early type is characterized by the presence of predominant immunoblastic paracortical infiltrate admixed with histiocytes. The healing phase of KFD is mostly represented by the presence of foamy histiocytes and referred to as xanthomatous type 36,37 .
Cases with abundant immunoblastic proliferation may be mistaken for high grade lymphoma. However, the presence of abundant histiocytic infiltrate, lack of complete lymph node effacement by B-lymphocytes Immunohistochemical markers and loss of clonality proof by B-surface immunoglobulin arrangement and T-cell receptor gene rearrangement, both favour the diagnosis of KFD 36 .
The mechanism by which KFD is linked to other autoimmune diseases remains unknown. Some researchers hypothesized that KFD was a T-cell mediated response to antigen stimuli in genetically susceptible individuals based on immunostains and histological findings 3 .
Affected patients with KFD may need to be followed for years due to the possibility of association with systemic lupus erythematosus. In addition, recurrences of Kikuchi disease can occasionally continue for many years 38 . Early detection and treatment of KFD to control active inflammation is crucial, owing to the presumptive reduction in the risk of consequent limb swelling and permanent lymphedema. KFD is nominated as a self-limiting disease in the majority of cases. However, supportive treatment, with non-steroidal anti-inflammatory drugs (sDIASN) is used for many patients to alleviate associated symptoms, such as fever, lymphadenitis-induced pain or arthralgia. Since etiology of this disease is still uncertain, definitive treatment remains challenging. In multiple studies corticosteroids were used for severe forms of disease (not responding to NSAIDS, prolonged course), relapsing lymphadenitis, or in patients with KFD manifestations (as listed above) 39 . Other reports described successful use of hydroxychloroquine and intravenous immunoglobulin (IVIG) for intractable disease 38 www.nature.com/scientificreports/ Our study has some limitations. First, it is a retrospective study. Second, the sample size of patients with KFD was relatively small to evaluate risk factors with statistical significance. In spite of these limitations, findings in this study should expand awareness of KFD, contribute to better understanding of clinical behaviour of this illness and highlight the importance of formulating a solid consensus regarding diagnosis and treatment protocols.
In conclusion, KFD may still be under-diagnosed in our part of the world, likely due to the non-specific mixed symptoms at presentation as well as to the lack of awareness among general practitioners and health care providers. Early diagnosis with tissue biopsy and treatment is essential to reduce associated morbidity.

Materials and methods
Study design. This is a retrospective study in which we identified patients diagnosed with KFD between January 2002 and January 2021. All patients included were diagnosed at King Abdullah University Hospital (KAUH). Jordan. The histopathology department's database was searched for KFD during this period. Biopsies were collected locally at KAUH and at affiliated hospitals, and then submitted to KAUH. Full review of patients' medical records was done. Patients were also contacted for follow up and verification whenever necessary. Data regarding demographic features, clinical presentation, laboratory findings, comorbidities and management protocols were obtained.
Work up for lymphadenopathy was driven by clinical evaluation. The following investigations were obtained as needed: complete blood count (CBC) and peripheral blood smear, Lactate dehydrogenase (LDH), Kidney function test, Liver function test and urine analysis, ESR and CRP. Screening for TB (sputum for Acid-Fast Bacillus (AFB), PPD testing), HIV (human immunodeficiency virus), and specific titers for Epstein-Barr virus, cytomegalovirus (CMV) and Toxoplasma species were rarely considered because patients presented almost always with regional lymph node enlargement.
Imaging studies included chest radiography, computerized tomographic (CT) scan for chest and/or abdomen, abdominal and cervical ultrasonography.
To retrieve reports of KFD in the Eastern Mediterranean region, the keywords (KFD, necrotizing lymphadenitis, histiocytic, Mediterranean, Middle East, Arab, and the individual name of each of the listed states in Table 1, were searched through PubMed or Medline, Embase Scopus, and Ovid databases. Full texts of the studies were obtained and year of publication, number of cases, main presenting symptoms were recorded. Histopathology. Lymph node biopsies were analyzed and reported by hematopatholohist. The histologic diagnosis of KFD was defined based on the presence of patchy areas of paracortical non-suppurative necrosis with the presence of abundant karyorrhectic debris. The necrotic areas are surrounded by mononuclear cells predominantly histiocytes including crescentic histiocytes. (Fig. 1).

Data availability
The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request. www.nature.com/scientificreports/