Diagnostic performance of routine blood parameters in periodic fever, aphthous stomatitis, pharyngitis, and adenitis syndrome

Abstract Background We aimed to investigate the difference between PFAPA and streptococcal tonsillitis (Strep Pharyngitis) by using blood parameters. We want to evaluate the relationship between periodic fever, aphthous stomatitis, pharyngitis, adenitis (PFAPA) syndrome, and tonsillitis by using NLR. Methods The data of 141 pediatric patients who had applied to our clinic between October 2016 and March 2019 and were diagnosed with PFAPA syndrome and tonsillitis were reviewed from hospital records. The demographic data of the study group were recorded, as were their WBC, neutrophil, and lymphocyte counts, NLR, and MPV values, which are obtained by proportioning these two counts. Results CRP and ESR values were significantly higher in the PFAPA group (p = 0.026 and p < 0.001, respectively). No significant difference was determined between the groups in terms of platelet count or lymphocyte count. Receiver operating curve analyses were calculated. The AUC was 0.713 ± 0.04 according to age, and the CRP was 0.607 ± 0.04 (95% confidence interval). Using a cutoff point of >49 months for age, the sensitivity was 0.71 and the specificity was 0.67. Conclusion With simple laboratory parameters, PFAPA syndrome can be differentiated from a diagnosis of tonsillitis. This may reduce the costs associated with unnecessary antibiotic use. However, these findings still need to be confirmed by other future studies.

quality of life, whereas misdiagnosis results in the overuse of antibiotics. The diagnosis of PFAPA may be challenging in persons who have underlying disorders that predispose them to upper respiratory tract illnesses such as allergic rhinitis and recurrent fever. For PFAPA syndrome, there is no test for diagnosis. It is possible to make a diagnosis with close monitoring and clinical suspicion. 5 Auxiliary diagnostic tools must be created due to the challenges in diagnosis.
Major acute phase protein, C-reactive protein (CRP), is a pentraxin family member and an essential component of the immune system. 6 CRP is still the biomarker most frequently utilized and dealt with, despite the fact that novel biomarkers are being used in several research studies. There are few noninvasive, broadly applicable biomarkers with high diagnostic reliability during the childhood.
Studies linked to noninvasive techniques have been carried out in the most recent research, giving birth to fresh expectations. In order to conduct a diagnose, complete blood count (CBC) and mean platelet volume (MPV) data are currently employed. The metrics that can be easily acquired as part of a CBC are the neutrophil-lymphocyte ratio (NLR) and MPV. NLR is calculated by dividing the absolute neutrophil count absolute lymphocyte count. It has been proposed as a sign of systemic inflammation. 7 It has been used in the differential diagnosis of inflammatory diseases from the neonatal period. 8 In disorders including familial Mediterranean fever, systemic lupus erythematosus, and juvenile idiopathic arthritis that are linked to systemic auto-inflammation, NLR has been investigated, and it has been proposed that this ratio can indicate the activity of the disease and the inflammatory response. 9 In order to diagnose and track inflammation, NLR and MPV data are now employed. NLR has been utilized in adult research to assess the presence and severity of sepsis. 8,9 Inflammation is indicated by this ratio. We aimed to investigate the difference between PFAPA and Strep Pharyngitis by using blood parameters. We want to evaluate the relationship between PFAPA and tonsillitis by using NLR. As far as we know, PFAPA is an additional autoinflammatory condition for which NLR or MPV have not been studied to date. The hospital's medical database provided patient laboratory and clinical data. All patients had a "rapid streptococcal antigen assay" as well as studies on their CBC, CRP, and ESR.

| Blood sampling and assays
For CBC and flow cytometry analysis, peripheral blood was collected in a tube containing ethylene diamine tetraacetic acid (EDTA) (1.2 mg/mL) (Sysmex Xt 2000, Japan). The ratio of neutrophil count to lymphocyte count was used to compute the NLR. The patients' White blood cell count (WBC), absolute neutrophil and lymphocyte counts, MPV, CRP, and ESR levels, as well as how many episodes they had had before admission, were noted. MPV, a measure of the platelets' average size and level of maturation, was also noted.
An automated dynamic analyzer (True line 200, Turkey) was used to measure ESR, while a gold standard digital quantitative analyzer (Cobas Integra 400) was used to measure CRP. Tubes containing liquid EDTA were used to measure CBC and ESR, while tubes containing a gel separator were used to measure CRP.

| Diagnosis of Strep Pharyngitis
It is advised to employ a diagnostic scoring system based on Centor or McIsaac to determine the likelihood that tonsillitis was brought on by hemolytic streptococci. A positive score of 3 should trigger a pharyngeal swab, fast test, or culture to detect hemolytic streptococci if therapy is being considered. 11 It is not necessary to perform routine blood testing for acute tonsillitis. After acute Strep Pharyngitis, standard cardiovascular diagnostics such as pharyngeal swabs or other routine blood tests, urinalyses, or EKG do not need to be repeated. The presence of positive growth in a throat culture, allows for the identification of group A beta hemolytic streptococcus. 11

| Power analysis
In our study, power analysis was performed for patients who were taken at regular intervals. Since the study reached 80% power level in 141 patients, the study was conducted on 141 patients.

| RE SULTS
A total of 141 children were involved in the study: 67 PFAPA patients and 74 with Strep Pharyngitis. Patients with PFAPA had smaller ages than tonsillitis group (p < 0.001), ( Table 1). The median age was 43 months  in the PFAPA group and 61 months  in the tonsillitis group. There was no significant difference between the groups in terms of the distribution of gender (p > 0.05). All PFAPA patients had a negative rapid streptococcal antigen assay result. The number of episodes before admission ranged between 2 and 8.
White blood cell count, neutrophil and lymphocyte levels, as well as PLT levels were similar in both groups (Table 1). Laboratory evaluation of study groups was given in Table 1 Receiver operating curve analysis for laboratory parameters were given in Table 2. The AUC was 0.713 ± 0.04 according to age and CRP was 0.607 ± 0.04 (95%, confidence interval) (Figure 1).   hand, it has been stated that diseases such as allergic rhinitis, which resembles recurrent upper respiratory tract infection, may also cause difficulties in diagnosis. 12 PFAPA syndrome as well is one of the important diseases that need to be considered in the differential diagnosis of patients presenting with fever. The disease appears to be more prevalent than assumed. In fact, the annual incidence of the disease in Norway was reported to be 2.3/10,000. 13  ESR than EBV tonsillitis. 17 The results were similar to our study, but the number of cases was lower and the age of patients was different to that in our study. To further understand the pathophysiology of this pediatric illness, Brown et al. 18 sought to profile blood cell and serum cytokine levels during the afebrile and febrile stages of periodic fever, aphthous stomatitis, pharyngitis, and adenitis (PFAPA) syndrome. They included a group of individuals with a median age of 4.9 years who were suffering "typical PFAPA" episodes. 18 Although T cell-associated cytokines IL7 and IL17 were repressed both during afebrile and febrile states, they found that IFN-induced cytokine IP10/CXCL10 was elevated following the onset of fever. 18 We did not look at these parameters, maybe they can be evaluated in future studies. The disease's cause is unknown; however, it is thought to be related to a process that is accompanied by an aberrant immune

F I G U R E 1
The ROC of mean CRP (A), ESR (B), NLR (C), and age (D). CRP and ESR was better than NLR and can be used for differential diagnosis. been suggested that NLR may be an inflammatory marker in these conditions. 23 The NLR rate was greater in instances of tonsillitis, and the sensitivity for tonsillitis was 0.62. It was observed that with a 3.24 cutoff point, the level of sensitivity and specificity were 62% and 59%, respectively. But, we did not compare with healthy children, maybe compared to healthy children, NLR rates in cases with PFAPA may be found to be higher. It is stated that MPV values in peripheral blood are seen to change in inflammatory processes. MPV therefore has been considered for use as an inflammatory marker, and evidence was obtained that MPV can be an indicator of autoinflammatory disorders. 23 In a study from our country, the role of MPV in PFAPA syndrome was investigated and patients with PFAPA had lower MPV levels during an attack and during a time without an episode than those seen in controls. 23 However, we did not find a significant relationship with MPV in our study. In another trial, 28 PFAPA syndrome patients who showed up at their clinic were investigated. 24 Healthy kids who visited the general pediatrics polyclinic at the same age and sex as the sick group were enlisted as the control group. 24 When patients with PFAPA syndrome were compared to the control group during the times between attacks, their mean platelet volumes (MPV) values were considerably lower than those of the control group. 24 In our study, the MPV value was lower in the PFAPA group, but we could not find a statistical difference.
We also have some limitations. Our most important limitation is that our study is a single center and the number of cases is low.
Another limitation was that the frequency of clinical findings for PFAPA was not noted. It would be useful to give what symptoms were expressed by patients (i.e., % with pharyngitis, % adenitis, % apthous stomatitis, etc). It would be better to propose a future studies to clarify how this predictive modeling of PFAPA diagnosis can be applied in other populations.

| CON CLUS ION
In conclusion, in cases where the age is >49 months, simple laboratory parameters can be used in the differential diagnosis of PFAPA syndrome and tonsillitis. The use of these parameters in particular can prevent the unnecessary use of antibiotics. CRP and ESR are the most important parameters in confirming a diagnosis and distinguishing PFAPA from acute tonsillitis. Again, we should keep in mind that the NLR rate will be higher in cases with tonsillitis. With simple laboratory parameters, PFAPA syndrome can be differentiated from a diagnosis of tonsillitis. This may reduce the costs associated with unnecessary antibiotic use. However, these findings still need to be confirmed by other future studies.
Another practical question is will this difference in the labs between PFAPA and strep tonsillitis provide more than obtaining a strep culture? Perhaps not, but where opportunities are limited and access to strep cultures is limited, the results of this study can be instructive.

AUTH O R CO NTR I B UTI O N S
Conceptualization, methodology, formal analysis and investigation, writing -review and editing: HO and AO.

ACK N OWLED G M ENTS
The authors thank all the contributors of this study.

CO N FLI C T O F I NTE R E S T S TATE M E NT
There is no conflict of interest in this study.

DATA AVA I L A B I L I T Y S TAT E M E N T
All the data related to this work are available at the corresponding author.