Necrotizing fasciitis (NF) is infrequent but highly lethal infection and is associated with systemic toxicity and a mortality rate of 30–60% [1] [2]. It affects the superficial fascia and subcutaneous tissue. Establishing the diagnosis of NF is difficult because nascent NF often appears deceptively benign and lack specific diagnostic clues [3]. Delay of diagnosis leads to delayed surgical debridement, which leads to higher mortality [1]. The manifestations of NF are similar to those of acute limb ischemia. Here, we introduce the case of necrotizing fasciitis accompanied with acute limb ischemia on left lower leg.

A 71-year-old male with a history of hypertension and stomach cancer complained of vomiting and dyspnea one day before admission to hospital. On admission, he was unconscious, with a Glasgow coma score of 3. Clinical examination revealed that the patient's state was critical, with a temperature of 39.3ºC, blood pressure 61/39, heart rate 144/min, respiratory rate 43/min, and oxygen saturation 94% on a non-rebreather mask at 15 L/min oxygen. The patient's left-sided respiratory sounds were decreased, with coarse crackles. The bowel sounds were normal and the abdomen was soft and non-tender. We intubated him in the emergency room because the patient was in shock with impaired consciousness. Laboratory findings revealed an elevated white blood cell (WBC) count of 1200/µL, C-reactive protein 27.1 mg/dL, creatinine kinase (CK) 2405 U/L, and creatinine 1.62 mg/dL. Arterial blood gas analysis revealed significant lactic acidosis (Table 1). Computed tomography (CT) scan revealed consolidation in the superior lobe of the left lung. Immunochromatographic membrane tests using urine sample for rapid detection of Streptococcus pneumonia antigen and Legionella antigen (BinaxNOW S. pneumoniae and BinaxNOW Legionella; Inverness Medical Innovations), were performed but gave negative results. Gram staining of the sputum revealed Gram-negative rods with neutrophils. The patient was diagnosed with pulmonary insufficiency associated with pneumonia and septic shock and admitted to the intensive care unit (Figure 1). We initiated therapy with vasopressors and broad-spectrum antibiotics (piperacillin/tazobactam and ciprofloxacin). On the same day, the patient's blood culture became positive for bacteremia with a Gram-negative rod. Therefore, direct hemoperfusion with a polymyxin B–immobilized fiber column was initiated.

On day-4, the skin of the left lower leg abruptly turned white and purpura developed. Doppler ultrasound was unable to detect blood flow in the left dorsalis pedis artery, and a CT scan showed severe stenosis of the left common iliac and femoral arteries. The patient's CK level had risen to 60,000 IU/L. The clinical manifestations, laboratory findings, and results of radiological imaging were suggestive of acute limb ischemia. We performed angiography, which revealed significant stenosis of the left common iliac artery (Figure 2); this finding was compatible with acute limb ischemia. We discussed whether or not we should perform revascularization because we did not know the precise time of onset of the limb ischemia. We reached the decision to insert a self-expanding stent into left common iliac artery and to perform a counter-incision (Figure 3) because the intracompartmental pressure of the left lower extremity was 70 mmHg. The patient's scrotum had also become swollen and erythematous on day-4, and its color had changed to purple on day-5 (Figure 4). We suspected Fournier gangrene and consulted urologists accordingly. Puncture of the scrotum revealed a serous, yellow, clear fluid, which was compatible with hydrocele testis, not Fournier gangrene. Despite the counter-incision, eight days after the patient's admission the color of his left lower extremity had not improved and the CK had risen rapidly further to 1, 500, 000 U/L. We considered other differential diagnosis including purpura fulinans caused by Streptococcus pneumonia, Streptococcus pyogenes, Vibrio vulnificus, and Neisseria meningitides. We therefore performed major amputation above the hip joint. The patient's general condition, including his vital signs, disseminated intravascular coagulation score, and oxygenation, improved temporarily after this intervention.

Unfortunately, two weeks later the patient developed candidemia as a complication of infection from his central venous catheter. Despite the administration of liposomal amphotericin-B to treat the candidemia, the patient died on hospitalization day-38 from multiple organ failure.

Pathology
Pathological examination of the amputated leg revealed muscle edema. Infiltration of WBCs (neutrophils, lymphocytes, histiocytes) was found around the fascia and fatty tissue. The striated muscle of the lower limb was not stained and showed eosinophilic changes in the sarcoplasmic reticulum. The muscle fibers were defiberized each other and were necrotic (Figure 5). This necrosis was compatible with acute compartment syndrome. The presence of inflammatory cell infiltrates around the fascia was indicative of necrotizing fasciitis (NF).

This patient developed lower extremity NF accompanied by severe sepsis and acute pneumonia caused by E. coli. Diagnosis of NF was difficult in this case, because the leg manifestations were similar to those of acute limb ischemia. Pathological examination of the leg finally helped us to differentiate NF from mere limb ischemia.

Diagnosing necrotizing fasciitis
Necrotizing fasciitis was first described by Jones in 1981. Although it is rare, mortality rates are very high at 30–60% [2]. Although it is reported that optimal surgical intervention is needed to treat NF, the condition is still challenging to diagnose NF. The literature reports that the use of three tools-macroscopic/microscopic tools, imaging studies, and laboratory findings-can help with the diagnosis [3].

Although macroscopic findings such as skin discoloration, blisters or bullae, crepitus upon palpation, skin necrosis, and subcutaneous gas [3] [4] are considered typical signs of NF, these findings are similar to those in acute limb ischemia [5]. Microscopic findings such as the presence of WBCs around the fascia and fatty tissue are helpful in establishing a diagnosis of NF, but it takes several days to get the results of such examinations. Indeed, in our case, it took several days to confirm NF in the specimen obtained during surgery. Imaging modalities such as ultrasonography, CT, and magnetic resonance imaging are also considered useful. These imaging studies have revealed that increasing thickness of the fascial layer with or without enhancement is a typical sign but is not specific to the diagnosis of NF, especially when a differential diagnosis of acute limb ischemia is being considered [6]. Among laboratory findings, the laboratory risk indicator for necrotizing fasciitis (LRINEC) score, which includes C-reactive protein, WBC count, hemoglobin level, sodium level, and glucose level, has been developed to distinguish NF from non-necrotizing soft tissue infections, but this scoring system is not helpful in differentiating NF from acute limb ischemia [7]. There are three categories of LRINEC score (points, probability of NF): low (<5, <50%), intermediate (6–7, 50–75%), and high (>8, >75). Although this score is not helpful in differentiating acute limb ischemia, it might have been useful as a reminder of the potential diagnosis of NF early on in this case. It is important not to miss the diagnosis of NF in every high-risk patient, even if acute limb ischemia is suspected, because the macroscopic findings are similar.

Necrotizing fasciitis associated with E. coli pneumonia and E. coli bacteremia
The most common microorganisms in necrotizing fasciitis are Streptococcus and Streptococcus spp [2]. Escherichia coli is also a major cause of NF and accounts for about 12% of all primary and secondary causative organisms [8]. Usually E. coli is seen in the normal intestinal flora and can be associated with gastroenteritis, hepatobiliary infection, or urogenital infection. Our patient had symptoms similar to those of enteritis but not of urinary tract infection or hepatobiliary infection. We could not definitively establish direct relationships among the NF, pneumonia, and bacteremia, likely because pneumonia rarely causes bacteremia (only in 5–14% of cases) [9]. We suspected that, in our patient, the enteritis could have caused bacterial translocation (with spread to the left lower extremity causing NF) and the vomiting might have induced aspiration pneumonia. However, we could not rule out the possibility that the E. coli in the sputum might have been a different strain from that in the blood culture [8]. Escherichia coli can cause pneumonia, especially in immunosuppressed patients: Gram-negative rods, including E. coli, colonize the throats of 50% of immunosuppressed patients [10].

In this case, the unusual, undetermined origin of the E. coli bacteremia associated with the patient's shock status, together with the pneumonia revealed by the CT imaging, misled us in such a way that we did not diagnose NF early. Early diagnosis and surgical intervention are needed to treat NF patients. We should not forget the possibility that any systemic infection can result in NF, and we should use caution in our clinical approach to skin color changes similar to those found in acute limb ischemia.

Although the diagnosis of necrotizing fasciitis (NF) is often difficult, the use of three tools-macroscopic/microscopic tools, imaging studies, and laboratory findings-can help with the diagnosis. It is important not to miss the diagnosis of NF in every high-risk patient, even if acute limb ischemia is suspected. In addition, considering systemic infection is also important when sputum culture grew E. coli.

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