Predicting necrotising soft tissue infections in people who inject drugs: poor performance of the Laboratory Risk Indicator for Necrotising Fasciitis score and development of a novel clinical predictive nomogram in a retrospective cohort with internal validation

INTRODUCTION

Necrotising soft tissue infections (NSTI) can threaten life and limb. Early identification and urgent surgical debridement are key for improved outcomes. NSTI can be insidious. Scoring systems, like the Laboratory Risk Indicator for Necrotising Fasciitis (LRINEC), exist to aid diagnosis. People who inject drugs (PWID) are high risk for NSTI. This study aimed to assess the utility of the LRINEC in PWID with lower limb infections and develop a predictive nomogram.

METHODS

A retrospective database of all hospital admissions due to limb-related complications secondary to injecting drug use between December 2011 and December 2020 was compiled through discharge codes and a prospectively maintained Vascular Surgery database. All lower limb infections were extracted from this database, dichotomised by NSTI and non-NSTI with the LRINEC applied. Specialty management times were evaluated. Statistical analyses involved: chi-square; Analysis of "variance"; Kaplan-Meier, and receiver operating characteristic curves. Nomograms were developed to facilitate diagnosis and predict survival.

RESULTS

There were 557 admissions for 378 patients, with 124 (22.3%; 111 patients) NSTI. Time from admission to: theatre and computed tomography imaging respectively varied significantly between specialties ( P =0.001). Surgical specialties were faster than medical ( P =0.001). Vascular surgery received the most admissions and had the quickest time to theatre. During follow-up there were 79 (20.9%) deaths: 27 (24.3%) NSTI and 52 (19.5%) non-NSTI. LRINEC ≥6 had a positive predictive value of 33.3% and sensitivity of 74% for NSTI. LRINEC <6 had a negative predictive value of 90.7% and specificity of 63.2% for non-NSTI. Area under the curve was 0.697 (95% CI: 0.615-0.778). Nomogram models found age, C-reactive protein, and non-linear albumin to be significant predictors of NSTI, with age, white cell count, sodium, creatinine, C-reactive protein, and albumin being significant in predicting survival on discharge.

CONCLUSION

There was reduced performance of the LRINEC in this PWID cohort. Diagnosis may be enhanced through use of this predictive nomogram.

Mortality associated with Fournier's gangrene remains unchanged over 25 years

OBJECTIVES

To report a case series of Fournier's gangrene (FG) from our institution, and to investigate its mortality over the past 25 years.

PATIENTS AND METHODS

Case notes of men presenting to our institution from 2013 to 2016 with FG were reviewed. As well as age, diabetic history, length of stay, length of stay in critical care, and mortality; we calculated (where possible) the Uludag Fournier's Gangrene Severity Index (UFGSI). Published studies and cases series reporting the mortality rates for FG were reviewed from 1993 to 2018. The size of the study, country of origin, average age and gender ratio were collected, alongside mortality.

RESULTS

Two of the 11 patients treated for FG at out institution died within 90 days of admission, a mortality rate of 18%. Predicted mortality was significantly higher. A total of 173 publications were identified from the Medical Literature Analysis and Retrieval System Online (MEDLINE) database published between 1993 and 2018, reporting data from 1975 to 2018. Analysis of heterogeneity, by both time and precision, supported exclusion of four retrospective coded database-driven studies from the analysis. From the remaining studies, mortality ranged from 0% to 42%. Of the 6152 reported cases, there were 1220 deaths, giving an overall mortality rate of 19.8%. There was no evidence of a significant change in the mortality rate for FG over time (P = 0.996).

CONCLUSIONS

In our case series, the mortality rate for FG was 18%, despite a higher predicated mortality (based on UFGSI scores). The treatment of FG remains appropriate resuscitation, aggressive surgical debridement, and critical care management. Perceived high risk of mortality should not deter aggressive management. Mortality due to FG does not appear to have changed over the past 25 years, and is estimated at 19.8%. In studies identifying cases of FG, careful attention should be paid to case definition, particularly when cases are being abstracted retrospectively from large coded databases.

Determining if Positive Predictive Value using Laboratory Risk Indicator for Necrotising Fasciitis is Applicable in Malaysian Patients with Necrotising Fasciitis

Introduction: Necrotising fasciitis (NF) is a rapidly progressive infection of the subcutaneous tissue and fascia which spreads rapidly. The scoring system of Laboratory Risk Indicator for Necrotising Fasciitis (LRINEC) developed by Wong et al has been proposed as a tool for distinguishing NF and other soft tissue infections (STI) in Singapore. We set out to establish whether the LRINEC score is applicable in our Malaysian setting.

Materials and Methods: A cross sectional study of all patients admitted to our hospital diagnosed with NF or To Rule Out NF (TRO NF) between January 1st 2016 to 30th June 2016. The sensitivity, specificity, positive and negative predictive values were then calculated for LRINEC score of ≥ 6 and ≥ 8.

Results: Fourty-four patients were identified with the diagnosis of NF or TRO NF in the study. Twenty-seven patients (61.4%) were deemed post-operatively as having NF and 17 patients (38.6%) not having NF. A sensitivity of 59.3% and specificity of 47.1% when a LRINEC score of ≥ 6 was taken with positive predictive value (PPV) of 64.0% and the negative predictive value (NPV) of 42.1%. When score ≥ 8 was taken, the sensitivity was 48.1% and specificity of 58.8% with PPV of 65% and NPV of 41.7%.

Conclusion: The low sensitivity and low PPV achieved in this study as well as other studies makes the LRINEC score unsuitable to be used solely to distinguish NF with other soft tissue infections.