Related Experiment Videos
The Limitations of Gram-stain Microscopy of Synovial Fluid in Concomitant Septic and Crystal Arthritis
Paul Stirling1, Mohammed Tahir2, Henry Dushan Atkinson1
1Edinburgh Trauma Unit Orthopaedic Surgery, Edinburgh, United Kingdom.
Background:
Rapid diagnosis of septic arthritis from Gram-stain microscopy is limited by an inherent false-negative rate of 25-78%. The presence of concomitant crystal arthritis in 5% of cases represents a particular diagnostic challenge.
Objectives:
This study aims to investigate the effects that a concomitant crystal arthropathy has on the ability of Gram-stain microscopy of synovial fluid to diagnose a septic arthritis.
Methods:
This is a 22-year retrospective cohort study. Inclusion criteria were a positive synovial fluid culture result with a positive clinical diagnosis of septic arthritis. Results were correlated with the presence or absence of urate and calcium pyrophosphate crystals, and Gram-stain result. During this time our collection and analysis methods remained unchanged. All samples were collected in Lithium Heparin containers. Chi-squared test with a p value < 0.05 was considered significant.
Results:
602 synovial fluid samples were included. 162 cases of concomitant crystal arthritis were identified (27%). Of these, 16 (10%) had an initial negative Gram-stain. Out of the 440 samples with no crystals detected, 18 (4%) had an initial negative Gram-stain microscopy result (p < 0.05).
Conclusion:
The incidence of concurrent septic and crystal arthritis may be higher than previously thought. Synovial fluid samples in concomitant septic and crystal arthritis are significantly less likely to have a positive Gram-stain at microscopy than in cases of an isolated septic arthritis. We would advise the clinician to maintain a high index of suspicion for septic arthritis in these patients.
Insights
Concomitant crystal arthritis significantly reduces the accuracy of Gram-stain microscopy for diagnosing septic arthritis, with a higher false-negative rate in these mixed cases. Clinicians should maintain a high suspicion for septic arthritis when crystals are present.
Area of Science:
- Rheumatology
- Infectious Diseases
- Microbiology
Background:
- Septic arthritis diagnosis via Gram-stain microscopy is hindered by a 25-78% false-negative rate.
- Concomitant crystal arthritis, present in 5% of cases, complicates accurate diagnosis.
Purpose of the Study:
- To evaluate the impact of co-existing crystal arthropathy on Gram-stain microscopy's diagnostic utility for septic arthritis.
Main Methods:
- A 22-year retrospective cohort study analyzed 602 synovial fluid samples.
- Inclusion criteria: positive synovial fluid culture and clinical diagnosis of septic arthritis.
- Results correlated Gram-stain findings with the presence of urate and calcium pyrophosphate crystals.
Main Results:
- 27% (162/602) of cases had concomitant crystal arthritis.
- 10% (16/162) of these mixed cases showed a negative initial Gram-stain.
- Compared to isolated septic arthritis, concomitant cases had a significantly higher rate of negative Gram-stains (p < 0.05).
Conclusions:
- The incidence of concurrent septic and crystal arthritis may be underestimated.
- Gram-stain microscopy is less sensitive for septic arthritis when crystals are present.
- Clinicians must maintain a high index of suspicion for septic arthritis in patients with crystal arthropathy.