Just Cellulitis...or something worse....

A 42-year-old female presents to the ED with one week of painful swelling of her left medial upper thigh. Her past medical history is remarkable for diabetes, morbid obesity, and rheumatoid arthritis, for which she takes immunomodulator therapy.

She had been seen by a PCM earlier in the week and was started on antibiotics. She returned to her PCM when she continued to have pain and swelling and she was then sent to the ER for evaluation. She was concerned because the redness was extending to her groin and lower abdomen.

On exam, she had redness and edema to her left lower abdominal wall extending midway down her thigh.

Initial x-ray image

What are the signs and symptoms suggestive of NSTI?

Symptoms- fevers, painful skin lesion (redness, swelling, warmth)
Signs- tachycardia, potentially hypotension. Skin warmth, edema, foul-smelling drainage, blistered or sloughing skin, crepitus.
*Pain out of proportion to exam is a concerning finding.

What workup should be performed?

Labs- CBC, electrolytes, lactate
Imaging- x-ray, ultrasound to rule out abscess, CT
An ultrasound was performed, but it was non-diagnostic. There was no obvious underlying abscess.

Why is ultrasound difficult with NSTI present?

Soft tissue air obscures the ultrasound images. Evidence of artifact on the ultrasound can be suggestive of NSTI.

What is the initial treatment of NSTI?

Like any septic patient, antibiotics, resuscitation, and rapid source control are paramount. For necrotizing soft tissue infections, source control requires expeditious surgical exploration and debridement.

Representative image from CT scan- upper thigh

Representative image from CT scan- lower abdominal wall

After starting broad-spectrum antibiotics and fluid resuscitation, the patient was taken to the operating room. Upon exploration, the tissue planes were easily dissected and there was copious grey-tinged malodorous fluid. The fluid was cultured to allow tailoring of antibiotic therapy. All necrotic tissue was excised and the wound was left open with gauze packing. She required low-dose norepinephrine during the case and had an elevated lactate. She remained intubated and was taken to the ICU. She returned each of the following 3 days until there was no more evidence of necrotic tissue or undrained infection. At that time a wound vac was placed and she returned for wound vac changes every 3 days.

Management of Necrotizing Soft Tissue Infection (NSTI)

Risk factors- diabetes, immunosuppression, malnutrition, obesity, IV drug use.

Bacteriology- often polymicrobial (Type 1), 20% are monomicrobial (Group A strep or S aureus). Culture with Gram + rods= Clostridia (Type III).

Diagnosis [1]

Patients may present with sepsis and multi-system organ failure.
Physical Exam- erythema or discolored skin, edema, pain out of proportion to exam, bullae, crepitus (late finding). Fever, hypotension.
Imaging- CT is more reliable than plain films. MRI is most effective but may delay care.
- Plain films- gas in soft tissues
- MRI- fascial thickening
- CT- soft tissue air, muscle edema, fluid collections, thickened non-enhancing fascia
Labs- leukocytosis, elevated lactate. Blood cultures.
LRINEC score- ≥6 is suspicious, ≥8 is strongly predictive. Low sensitivity, not reliable to rule-out NSTI.[1,2]
- CRP ≥150= 4 points
- WBC 15-25= 1 point, >25= 2 points
- Hgb 11-13.5= 1 point, <11= 2 points
- Sodium <135= 2 points
- Cr >1.4= 2 points
- Glucose >180= 1 point
Intraoperative findings: dishwater-like fluid is frequently encountered. Tissue planes easily separate, including the soft tissue separating from the underlying fascia.

Management

Rapid resuscitation, antibiotics, and surgical excision.
If there is a high clinical suspicion, don't delay surgery to await imaging.
Obtain tissue culture intraoperatively.

Antibiotics

Broad-spectrum until cultures available- vanco OR linezolid + pip/tazo OR carbapenem OR ceftriaxone/metronidazole
S aureus- nafcillin, cefazolin, vancomycin, clindamycin
Group A strep OR Clostridium- clindamycin and penicillin.

Adjuvant Therapies

IV immunoglobulin- neutralize Strep or clostridia toxin.
Hyperbarics- no clear benefit.
Immunomodulators?

There are comprehensive reviews of the current practices regarding diagnosis and treatment of NSTI in Lancet and the New England Journal of Medicine.[3,4]

References