Value of the systemic immuno-inflammatory index as a diagnostic tool for the main causes of knee pain presenting in the emergency department in Yaoundé, Cameroon.

BACKGROUND

In a context of limited resources, differentiating the etiologies of knee pain in the emergency department can be challenging. Full blood count is one of the constantly available tests with many under-exploited indices, such as the systemic immuno-inflammatory index (SII). The present study aimed to assess its diagnostic value.

METHODS

A cross-sectional study was conducted from January to May 2024 on adults with a confirmed diagnosis of one of the three main causes of knee pain seen in the emergency department of Yaoundé Central Hospital. The SII (platelet count x neutrophil count/lymphocyte count) was compared between etiological groups using ANOVA. The ROC curve was used to determine its sensitivity (Se) and specificity (Sp) in differentiating these etiologies.

RESULTS

The three main causes were knee osteoarthritis flare (KOA; 126 cases), acute gouty arthritis (49 cases), and bacterial septic arthritis (SA; 25 cases). The SII differed significantly among the three groups: it was lower in KOA (mean 242, standard deviation 165) and higher in bacterial septic arthritis (mean 1234, standard deviation 557). An SII value below 271 allows differentiation between KOA and gout or SA (Se = 78%, Sp = 67%), while an SII value above 487 permits differentiation between gout and septic arthritis (Se = 95%, Sp = 75%).

CONCLUSION

The SII is an interesting diagnostic tool for cases of knee pain seen in emergency departments. However, it would be appropriate to evaluate it on a larger sample before integration into the decision tree in a context of limited resources.