Application of a Novel Diagnostic Rule in the Differential Diagnosis between Acute Gouty Arthritis and Septic Arthritis

Septic arthritis and gout are major diseases that should be suspected in patients with acute monoarthritis. These two diseases are clinically similar and often indistinguishable without the help of synovial fluid analysis. Recently, a novel diagnostic rule for gout without synovial fluid analysis was developed and showed relevant performances. This study aimed to determine whether this diagnostic rule could perform well in distinguishing gout from septic arthritis. The diagnostic rule comprises 7 clinical and laboratory variables, each of which is given a specified score. The probability of gout is classified into 3 groups according to the sum of the scores: high (≥ 8), intermediate (> 4 to < 8) and low probability (≤ 4). In this retrospective study, we applied this diagnostic rule to 136 patients who presented as acute monoarthritis and were subsequently diagnosed as acute gout (n = 82) and septic arthritis (n = 54) based on synovial fluid analysis. The mean sum of scores of acute gout patients was significantly higher than that of those with septic arthritis (8.6 ± 0.2 vs. 3.6 ± 0.32, P < 0.001). Patients with acute gout had significantly more 'high', and less 'low' probabilities compared to those with septic arthritis (Eta[η]: 0.776). The prevalence of acute gouty arthritis, as confirmed by the presence of monosodium crystal, was 95.5% (61/64), 57.5% (19/33), and 5.1% (2/39) in high, intermediate and low probability group, respectively. The recently introduced diagnostic rule properly discriminates acute gout from septic arthritis. It may help physicians diagnose gout in cases difficult to be differentiated from septic arthritis. Graphical Abstract Keywords: Gout, Arthritis, Infectious, Diagnosis, Differential, Diagnostic Test INTRODUCTION Acute gout and septic arthritis are the major diseases that should be suspected in patients presenting as acute monoarthritis (1). The differential diagnosis of these two diseases is important because incorrect diagnosis and misled treatment can lead to undesirable outcomes such as joint destruction or unnecessary surgical debridement. However, differentiating acute gout from septic arthritis can be difficult on clinical examination since they are clinically similar. Both of these two diseases commonly involve a single joint and accompany severe joint inflammation. Septic arthritis often accompany systemic features such as fever and chilling (1), which can also be seen in patients with gout, though they are not as common in gout as in septic arthritis. Diagnosis of both gout and septic arthritis can be established by synovial fluid analysis: demonstrating monosodium urate crystal (MSU) for gout by a polarized microscope and bacteria by Gram staining or culture in the case of septic arthritis. However, synovial fluid analysis is often impractical in real practice and the differential diagnosis between gout and septic arthritis might be problematic without the help of synovial fluid analyanalysis. Recently, a novel diagnostic rule for acute gout without joint fluid analysis was introduced and showed a good performance in predicting the possibility of gout (2). However, the first study validating this rule included only 2 cases with septic arthritis. We applied this diagnostic rule to the patients with gout and those with septic arthritis and determined whether this rule properly diagnoses gout and excludes septic arthritis in the setting of acute monoarthritis.