May 2025

70Year-old Female with Left Thigh Redness and Pain

Author: Benjamin Caviston, MD PGY-3

Peer Reviewers: Lee LaRavia, DO; Dan Kaminstein, MD

Learning Objectives:

  • List/discuss DDX of Skin/Soft tissue Infections
  • Discuss use of US in the workup
  • Discuss the US characteristics/findings associated with NSTI
  • Review of recent literature regarding POCUS in diagnosis of NSTI

Case Presentation

  • 70F with history of lung cancer on immunotherapy presents with 1 day of progressive left thigh redness/pain. Noticed pain and redness to medial thigh which has rapidly progressed over course of the day, now has area of central bruising
  • T: 36.9 °C (Oral) HR: 96(Peripheral) RR: 24 BP: 101/73 SpO2: 100% WT: 53.200 kg 
  • Exam: Large area of erythema, warmth, induration to the left medial thigh, central area of ecchymosis, No Crepitus, No Knee effusion
  • DDx: Necrotizing Fasciitis, Cellulitis, Erysipelas, Abscess, Pyomyositis, Septic Arthritis, Deep Venous Thrombosis, Superficial Thrombophlebitis

Differential Diagnosis

  • Pulmonary: Asthma/COPD. Pneumonia, pneumothorax
  • Cardiogenic: PE, ACS/MI, CHF, cardiomyopathy, dysrhythmia, cardiac tamponade, valvular disease, post-viral peri/myocarditis
  • Other: Cancer, Tuberculosis, HIV, Chagas,  Endomyocardial Fibrosis (EMF), Schistosomiasis, hookworm, syphilis, Rheumatic heart disease

POCUS Images 

  • Medial Thigh Soft Tissue

POCUS Interpretation

  • Cobblestoning: Fat lobules separated by hypoechoic fluid (Blue arrows)
    • Seen in any cause of tissue edema

cobbllstoning

  • Hyperechoic lines (Red Arrow) with dirty white shadowing (Green Arrows)
    • This Finding is suggestive of gas within the Soft Tissues

hyperechoiclines

  • Fluid Stripe along Fascial Plane

fluid stripe

Diagnosis and Case Disposition

  • This patient had Necrotizing Fasciitis of the Thigh
  • Surgery was consulted and agreed to operate based on exam and POCUS before any labs and formal imaging could be completed
  • Unfortunately Patient rapidly decompensated and went into Cardiac Arrest before being taken to OR
  • Blood Cultures ultimately grew Clostridium Septicum

Pathophysiology and Diagnosis

  • Rapidly progressive infection along fascial planes
  • Typically Polymicrobial
    • Anaerobes: Clostridium
    • Gram Positives: Streptococcus (GAS), Staphylococcus (MRSA)
    • Gram Negative: Pseudomonas, Klebsiella, Vibrio Vulnificus
  • Most sensitive diagnostics are CT and MRI but both have low specificity (Tso 2018)
    • CT Sensitivity 80%
    • MRI Sensitivity 93%

Literature Review

  • Castleberg et al 2014; Proposal of the STAFF Protocol, evaluating for S ubcutaneous T hickening, A ir and F ascial F luid to rule in Necrotizing Fasciitis
    • Not Validated but is a useful mental framework
  • Marks et al 2023; Systematic Review of imaging findings associated with necrotizing fasciitis, only 3 studies and 221 cases included
    • Fluid Accumulation: 85% Sensitive 45% Specific
    • Thickened Fascia: 67% Sensitive 55% Specific
    • Subcutaneous Gas: 6% Sensitive 100% Specific
  • Lahham et al 2022; Prospective study (N=64) of patients presenting to ED with clinical concern for NSTI, results of POCUS were compared to CT and Surgical findings sensitivity of 100% and specificity of 98.2%
    • Small study, Sensitivity/Specificity higher than prior studies, 100% of positive cases had presence of soft tissue gas which does not reflect reality

Take Away Points

  • Necrotizing Fasciitis is an emergent and cannot miss diagnosis
  • CT and MRI are the most sensitive studies (poor sensitivity) but delay time to diagnosis
  • POCUS findings include gas within tissues and fluid along fascial planes
  • US is useful to Rule-in the diagnosis of necrotizing fasciitis but ruling out should be done in conjunction with advanced imaging (CT or MRI), scoring systems and surgical consultation
  • Consider routine use of POCUS in patients whose presentation is concerning for NSTI to facilitate rapid treatment and consultation

References

  • Castleberg, E., Jenson, N., & Am Dinh, V. (2014). Diagnosis of necrotizing faciitis with bedside ultrasound: the STAFF Exam. Western Journal of Emergency Medicine, 15(1), 111.
  • Lahham, S., Shniter, I., Desai, M., Andary, R., Saadat, S., Fox, J. C., & Pierce, S. (2022). Point of Care Ultrasound in the Diagnosis of Necrotizing Fasciitis. The American journal of emergency medicine, 51, 397–400. https://doi.org/10.1016/j.ajem.2021.10.033
  • Marks A, Patel D, Sundaram T, Johnson J, Gottlieb M. Ultrasound for the diagnosis of necrotizing fasciitis: A systematic review of the literature. Am J Emerg Med. 2023 Mar;65:31-35. doi: 10.1016/j.ajem.2022.12.037. Epub 2022 Dec 22. PMID: 36580698.
  • Tso D & Singh A. Necrotizing Fasciitis of the Lower Extremity: Imaging Pearls and Pitfalls. Br J Radiol. 2018;91(1088):20180093. doi:10.1259/bjr.20180093 - Pubmed