Background: Necrotizing soft tissue infections (NSTIs) are rare, devastating diseases frequently caused by beta-hemolytic streptococci. Diagnosis is challenging, and mortality rates are high. Several guidelines recommend tissue biopsies in routine patient management. Sampling and biopsy classification are not standardized and methods not validated. We aimed to study the quality of tissue biopsy as routine diagnostic in NSTIs.
Method: Retrospective cohort study of adult patients undergoing surgery due to suspected NSTI where tissue biopsy was taken as part of standard patient management. Biopsies were evaluated according to a proposed histopathologic classification and independently assessed by two pathologists. Interrater reliability and diagnostic accuracy was determined. A clinical composite endpoint was used to evaluate association to histopathologic stages.
Results: Altogether 75 patients were included, 55 NSTI cases and 20 controls. Streptococcus pyogenes was confirmed in 27% (n=15), and S. dysgalactiae in 20% (n=11) of the NSTI cases. In all biopsies, the sensitivity of histologic diagnosis was 75% and the specificity 80%. Positive predictive value was 91% and negative predictive value 53%. Interrater reliability for histopathologic staging was moderate at 0,5. The most severe histological stage, indicating a stronger neutrophilic response, was associated with an improved outcome (OR 3,4, 95% confidence interval 1,00-11,61 (p=0,046)).
Conclusion: Our findings suggest that tissue biopsies are of low clinical accuracy. The interrater reliability among experienced pathologists was only moderate. Altogether, these findings advocate discouraging routine use of histopathologic evaluation as part of contemporary diagnostic management of patients with suspected NSTI.