Discussion
This study emphasizes that despite best surgical judgment and the use of predictive models, there are a number of patients who will not have an NSTI at the time of surgical exploration. Our study is unique in that our patients all went to operation with a working diagnosis of NSTI—that is, the diagnosis of cellulitis or abscess occurred at the time of operation (and not pre-emptively). Our study adds to existing literature that the differences between patients with NSTI and non-NSTI can be extremely subtle, and we propose that there may be an acceptable rate of negative exploration for this disease process. For us it was 20%.
Previous work corroborates the difficulty in expediently diagnosing NSTI. Only 14% to 39% of necrotizing fasciitis is correctly identified at initial presentation.7 14 25 26 Our study is unique in that we expanded our study group beyond necrotizing fasciitis to all NSTI. Further, our study indicates that even experienced clinical judgment can be wrong. Other surgical disease processes with diagnostic challenges, such as appendicitis, have been extensively studied with a historical negative appendectomy rate of approximately 15%.27–29 Over time, groups at increased risk of negative appendectomy such as women and children have been identified,27–32 and the overall rate of negative appendectomy has declined to 3% to 4%.29 30 Our study establishes an overall negative exploration rate of 20%, which with time may be validated or refuted and improved by subsequent research.
In this study, patients operated on for NSTI were clinically similar preoperatively regardless of their intraoperative findings. They had indistinguishable degrees of fever and tachycardia, with remarkably similar rates of septic shock. ‘Hard signs’ of NSTI such as bullae, violaceous changes, and crepitus were seen in both groups. Some studies consider hard signs a late finding in NSTI and report them in less than half of patients.1 2 6 7 9 10 12 14 15 33 Fernando et al found that the lack of pathognomonic physical examination findings was insufficient to rule out NSTI.17 We found relatively low numbers of these signs in our patients as well, but even more importantly, we demonstrate that these hard signs can also be present in patients with non-NSTI further confusing the diagnosis.
Similar to prior studies, we found the lower extremity to be the most common site of NSTI.7 11–13 26 33–37 Pelvic, perineal, and perianal presentations were significantly more common in the NSTI cohort, and this region had the lowest rate of negative exploration (6.9%). It is unclear the full reason for these trends, but surgeons may have a lower threshold to explore an extremity. Alternatively, Fournier’s may represent a unique disease entity or the perineum a unique environment that predisposes the patient to NSTI. Larger numbers would be needed, but it is possible that differing body areas also have varying ‘acceptable’ rates of negative exploration.
Notable laboratory differences in the patients with NSTI included more profound leukocytosis and hyponatremia. When looking at the IQRs, however, there is considerable overlap between the two groups, thus although statistically significant, these differences do not seem clinically relevant. Patients with negative explorations had leukocytosis up to 23 000 and were consistently mildly hyponatremic after correcting for glucose levels, just like patients with NSTI. Thus, whereas leukocytosis and hyponatremia have been integrated into multiple predictive models of NSTI,8 14 15 we find that they also occur in patients without NSTI.
The relative incidence of polymicrobial versus monomicrobial infections varies considerably,6 but polymicrobial infections are often the most common etiology of NSTI.1 3 5 7 9 11 12 21 22 34 37 Diabetes has been associated with polymicrobial NSTI infections, and the higher prevalence of diabetes in our NSTI group likely contributed to the relatively higher frequency of polymicrobial infections.36 Monomicrobial isolates previously associated with NSTI (Streptococcus and S
.
aureus sp) were also seen in the non-NSTI cohort. Why the same causative organism results in varying degrees of virulent infections remains unclear. This is likely attributable to host factors that have yet to be fully elucidated and an area for future research.34
The cohort of eight patients who had initial operative diagnoses of cellulitis and then returned to the operating room due to failure to improve is a small, but fascinating group. We found no specific trends to predict who these patients would be. They had no unique demographics or clinical presentations, and their pathogens represented a varied microbiology. Only one of these patients died, so this group was not the source of similar mortality we reported for the NSTI and non-NSTI patients. Although one assumption is that the surgeon missed the diagnosis during the first operation, it should be recalled that this was the main intent of the operation so probing and evaluating for tissue viability was the standard. Alternatively, this cohort could support the concept that NSTIs are an evolving disease process and further explain what other authors have reported as a delay to diagnosis. We use this data to recommend that surgeons continue to follow patients who they determined to have a negative exploration and go back for further exploration if the patient fails to improve.
Patients with NSTI and those with negative explorations had similar mortalities indicating the severe cellulitis can also be a serious disease process. The increased number of debridements and amputations in the NSTI cohort is likely secondary to the destructive nature of NSTI and the need to gain surgical source control. Increased ICU LOS in NSTI may reflect the time needed to obtain source control or advanced wound care needs. The overall increased LOS is likely secondary to numerous factors as patients with NSTI require substantial resources during their treatment.3 14 15 This includes reoperation (debridements, wound VAC changes, and skin grafts), need for physical therapy, and patient disposition issues.
Limitations to this study include that it is retrospective in nature and conducted at a single institution. Our institution is a safety-net hospital and patients may present later in their disease course. We may also have different thresholds to operate on patients with suspected NSTI than other institutions. A final potential criticism of this study is that we do not routinely use the absolute value of LRINEC in making a decision to operate. As an experienced trauma and acute care surgery service, a negative LRINEC score would not dissuade our team from operating on a patient in septic shock with findings concerning for NSTI.