>Skin and Soft Tissue Infections: A PoCUS Guided Approach

Medical Student Clinical Pearl – November 2020

 

Robert Hanlon

@roberthanlon12

Year: 4
DMNB Class of 2021
 

Reviewed and Edited by Dr. David Lewis

All case histories are illustrative and not based on any individual

 


Case Report

A 25yr old male presents with a 3 day history of a red swollen foot following an insect bite. He has no past medical history. On examination there is some erythema and swelling on the dorsum of the left foot. Palpation is very tender.

You are aware of recommended guidelines that advise I&D for purulent infections and decide to proceed with the procedure. Despite trying to freeze the area with lidocaine, the procedure is still painful and no pus is drained. You point to the minimal serosanguinous exudate and sheepishly suggest to the patient that the I&D was successful and that a course of antibiotics will resolve this issue.


Skin and Soft Tissue Infections: A POCUS Guided Approach

Skin and soft tissue infections (SSTIs) have a variety of potential causes, ranging in severity from mild infections like cellulitis to abscess all the way to life-threatening causes like necrotizing fasciitis.1 SSTIs are commonly encountered in the emergency department, with cellulitis and abscesses being the two most common.2 It is important to be able to recognize SSTIs and provide appropriate treatment. Abscesses require invasive management, whereas cellulitis is treated with systemic therapies; therefore, it is important to be able distinguish the different between the two types. Doing so can be difficult because of the hidden nature of abscesses. However, ultrasound can be a useful tool in establishing the presence of an abscess. This article is a review of the clinical approach and treatment for SSTIs, focusing on cellulitis and abscesses, as well as the use of ultrasound in helping to establish the diagnosis.


Approach

Clinical suspicion is the initial step in the diagnosis of SSTIs. These infections have multiple causes; therefore, obtaining a detailed history is crucial. Information about immunocompromised state, place of residence, travel, any recent trauma or surgery, previous antimicrobial use, lifestyle, hobbies, and animal bites is essential to developing an adequate differential diagnosis.3

A good understanding of the normal skin flora and common infectious organisms is key to assessing SSTIs. The most commons organisms implicated in SSTIs are Staphylococcus aureus and Streptococcus species.4-6 Methicillin resistant S. aureus (MRSA) being an important strain that has increased in prevalence in the past 20 years. Risk factors such as presence of abscess, intravenous drug use, previous MRSA status, antibiotics within 8 weeks, diabetes mellitus, and previous hospital admission within the last year increase the likelihood of the infection being cause by MRSA.4-6

Physical examination findings are crucial for establishing the presence of an SSTI; the typical criteria are a superficial lesion with the classic inflammatory findings of redness (rubor), swelling (tumor), warmth (calor), and pain (dolor).1,2,7 An abscess is defined as a fluctuant mass of puss localized and buried within a tissue, organ, or potential space; however, clinically it can be hard to determine to presence of this mass.2,7 Other associated signs and symptoms, such as crepitus, bullae, and hemorrhage, may be present upon diagnosis or may develop later during the course.2,7 Due to overlapping clinical presentations of the different SSTIs, it can be difficult to differentiate between them.


Cellulitis – No Abscess
Cellulitis – Possible Abscess
Abscess
Early Abscess

Assessment with POCUS:

Due to the similarities between different SSTI cutaneous findings and their different treatments, it is important to establish if there is an abscess present. It was common, before the introduction of ultrasound, to perform a blind needle aspiration of the infected area in order to determine the presence/absence of an abscess.8,9 However, this subjects that patient to the risks of an invasive procedure as well as pain. On the other hand, treating infection with empiric antibiotics in the presence of an unknown abscess delays drainage and allows for potential worsening of the infection.8,9

A study by Tayal et al. demonstrated that the use of ultrasound was beneficial in patients who had both low and high pretest probability for needing incision and drainage. In patients suspected of having simple cellulitis (low pretest), ultrasound was used to change management in over half of participants; establishing the need for drainage due to imaging of a fluid collection. The opposite was true in the patients suspected of having an abscess (high pretest); the study found that ultrasound was able to determine that more than half of this group did not need drainage, because of the absence of a fluid collection on imaging.10 Other studies have had similar findings, but the percent change in management was slightly lower.11

A study by Barbic et al. demonstrated that POCUS provided a rapid, non-invasive, painless, and easily repeatable test, that distinguished between abscess and cellulitis in the vast majority of cases. Their analysis concluded that POCUS had a sensitivity of 96.2% and a specificity of 82.9% in diagnosing the presence of an abscess.12 They concluded that POCUS can accurately diagnose abscess in paediatric and adult populations and is likely superior to clinical examination.12


Cobblestones

Classic finding for cellulitis (but not specific to cellulitis). There will be hyperechoic lobules of subcutaneous fat surrounded by relatively hypoechoic inflammatory fluid.13

Cobblestone – Cellulitis

Purulent Fluid Collection

Classic finding for an abscess; have a rounded shape of anechoic or hypoechoic fluid collection, and there will be surrounding areas of cobblestones from the overlying cellulitis.13 As well, there should be no color flow if doppler is applied to the area (helping to distinguish from lymph node or vessel).14

Abscess – Anechoic Collection
Possible Abscess or Lymph Node? – This is a lymph node – see below
Colour flow differentiates lymph node from abscess

Necrotizing Fasciitis

Because you do not want to miss it! Findings via ‘STAFF’; subcutaneous thickening, air, and fascial fluid.14 Note, that ultrasound does not to exclude the diagnosis. Also need clinical correlation to increase suspicion of such a serious infection.15

Necrotizing Fasciitis – STAFF

Treatment:

According to The Infectious Diseases Society of America (2014) guidelines, management of SSTIs is differentiated based on the presence/absence of purulence (i.e. abscess/fluid collection). They recommend that all purulent infections be treated with incision and drainage, with more severe infections (signs of systemic involvement) being cultured with sensitivities in order to add antibiotics to the treatment.16 Otherwise, non-purulent infections are to be treated with systemic antibiotics; the severity of the infection determining the route and choice of agent.16

Antibiotic therapy, in addition to incision and drainage of a skin abscess, is suggested for patients with any of the following:17

  • Single abscess ≥2 cm or multiple abscesses
  • Large are of surrounding cellulitis
  • Patients with immunosuppression or other comorbidities
  • Signs of systemic involvement (fever > 38°C, hypotension, or tachycardia)
  • Poor clinical response to incision and drainage alone
  • Presence of an indwelling medical device
  • High risk for adverse outcomes with endocarditis (these include a history of infective endocarditis, presence of prosthetic valve or prosthetic perivalvular material, unrepaired congenital heart defect, or valvular dysfunction in a transplanted heart)
  • High risk for transmission of aureus to others (such as in athletes or military personnel)

 

Horizon Health’s local trends recommend the following (see guideline or Spectrum app for full details)

Severity of Infection

 

 

Antibiotic

Mild

Moderate

Severe

Cephalexin 500 – 1000mg PO q6h x 5 days

ceFAZolin 2 g IV q8h x 5 days

ceFAZolin 2 g IV q8h +/- Clindamycin 900 mg IV q8h

If true beta-lactam allergy

Cefuroxime 500 mg PO BID or TID x 5 days

Clindamycin 600-900 mg IV q8h x5 days

 

If MRSA suspected

Septra 800/160 mg or 1600/320 mg PO q12h x 5 days

Vancomycin 25-30 mg/kg IV once then 15mg/kg IV q8 to q12h x 5 days

ADD Vancomycin 25-30 mg/kg IV once then 15mg/kg IV q8 to q12h

 


Some research is suggesting that POCUS can take the assessment of abscesses one step-further and impact management based on the depth and size of the fluid collection seen in imaging. Russell et al. found that abscesses less than 0.4cm below the skin surface could be effectively treated without incision and drainage.18 Another study found that patients, with skin abscesses less than or equal to 5cm in diameter, treatment with oral antibiotics in combination with incision and drainage had improved short-term outcomes compared to those patients treated with the procedure alone.18 While as mentioned above, UpToDate, suggests that antibiotics be used in single abscess greater than 2 cm in size. As well, research has found that ultrasound guided incision and drainage provides lower failure rates (less recurrent infections or multiple incisions) compared to blind incision and drainage. Likely due to better visualization of the abscess and more adequate initial drainage.19


Limitations

There are some limitations to POCUS for SSTIs: ultrasound imaging and interpretation rely on the user’s ability to obtain high-quality images in order to assess whether an abscess is present. It is important for the user to be familiar with different findings on ultrasound to guide appropriate treatment. An abscess may appear hypoechoic, hyperechoic, or anechoic (depending on tissue contents), and usually has posterior acoustic enhancement.19 Determining if it is drainable can be difficult due to this variability in imaging, and it is also quite common for early abscesses to present like cellulitis with erythema, no fluctuance, and an ultrasound that is negative for a fluid collection.20 In cases of a suspected evolving abscess, sometimes referred to as a non-ripe abscess, supportive care, including warm compresses, pain control, and close follow-up, is recommended.20 The practitioner may treat this like cellulitis; however, the patient may return with perceived failure of therapy if discharge advice does not include the possibility of of an abscess forming over time.


Abscess examples from the SJ archives


References

  1. Moffarah AS, Al Mohajer M, Hurwitz BL, Armstrong DG. Skin and Soft Tissue Infections. Microbiol Spectr. 2016 Aug;4(4). doi: 10.1128/microbiolspec.DMIH2-0014-2015.

 

  1. Martinez, N. “Skin and Soft-Tissue Infections: Itʼs More Than Just Skin Deep.” Advanced Emergency Nursing Journal, vol. 42, no. 3, 2020, pp. 196–203.

 

  1. Cieri, B., Conway, E., Sellick, J., & Mergenhagen, K. (2019). Identification of risk factors for failure in patients with skin and soft tissue infections. The American Journal of Emergency Medicine, 37(1), 48-52.

 

  1. Borgundvaag, B., Ng, W., Rowe, B., Katz, K., Farrell, Brian, Guimont, Chantal, . . . Gregson, Dan. (2013). Prevalence of methicillin-resistant Staphylococcus aureus in skin and soft tissue infections in patients presenting to Canadian emergency departments. CJEM, 15(3), 141-160.

 

  1. Esposito, S., De Simone, G., Pan, A., Brambilla, P., Gattuso, G., Mastroianni, C., . . . Savalli, F. (2019). Epidemiology and Microbiology of Skin and Soft Tissue Infections: Preliminary Results of a National Registry. Journal of Chemotherapy (Florence), 31(1), 9-14.

 

  1. Stenstrom, R., Grafstein, E., Romney, M., Fahimi, J., Harris, D., Hunte, G., . . . Christenson, J. (2009). Prevalence of and risk factors for methicillin-resistant Staphylococcus aureus skin and soft tissue infection in a Canadian emergency department. CJEM, 11(5), 430-8.

 

  1. Spelman, D., Baddour, LM. (2020). Cellulitis and skin abscess: Epidemiology, microbiology, clinical manifestations, and diagnosis In: UpToDate, Post TW (Ed), UpToDate, Waltham, MA. Retrieved November 11, 2020. From: https://www.uptodate.com/contents/cellulitis-and-skin-abscess-epidemiology-microbiology-clinical-manifestations-and-diagnosis?search=abscess%20treatment&topicRef=110530&source=see_link#H2443336514

 

  1. Comer, Amanda B. “Point-of-Care Ultrasound for Skin and Soft Tissue Infections.” Advanced Emergency Nursing Journal, vol. 40, no. 4, 2018, pp. 296–303.

 

  1. Gaspari, R., Sanseverino, A., & Gleeson, T. (2019). Abscess Incision and Drainage With or Without Ultrasonography: A Randomized Controlled Trial. Annals of Emergency Medicine, 73(1), 1-7.

 

  1. Tayal, V., Hasan, N., Norton, H., & Tomaszewski, C. (2006). The Effect of Soft‐tissue Ultrasound on the Management of Cellulitis in the Emergency Department. Academic Emergency Medicine, 13(4), 384-388.

 

  1. Alsaawi, A., Alrajhi, K., Alshehri, A., Ababtain, A., & Alsolamy, S. (2017). Ultrasonography for the diagnosis of patients with clinically suspected skin and soft tissue infections: A systematic review of the literature. European Journal of Emergency Medicine, 24(3), 162-169.

 

  1. Barbic, D., Chenkin, J., Cho, D., Jelic, T., & Scheuermeyer, F. (2017). In patients presenting to the emergency department with skin and soft tissue infections what is the diagnostic accuracy of point-of-care ultrasonography for the diagnosis of abscess compared to the current standard of care? A systematic review and meta-analysis. BMJ Open, 7(1), E013688.

 

  1. Atkinson DP, Bowra J, Harris T, Jarman B, Lewis D, editors. Point of Care Ultrasound for Emergency Medicine and Resuscitation. Oxford University Press; 2019. pp. 140, 199-200.

 

  1. Gottlieb, M., Schmitz, G., Grock, A., & Mason, J. (2018). What to Do After You Cut: Recommendations for Abscess Management in the Emergency Setting. Annals of Emergency Medicine, 71(1), 31-33.

 

  1. Castleberg, E., Jenson, N., & Dinh, V. (2014). Diagnosis of necrotizing faciitis with bedside ultrasound: The STAFF Exam. The Western Journal of Emergency Medicine, 15(1), 111-113.

 

  1. Stevens, D., Bisno, A., Chambers, H., Dellinger, E., Goldstein, E., Gorbach, S., . . . Wade, J. (2014). Practice guidelines for the diagnosis and management of skin and soft tissue infections: 2014 update by the infectious diseases society of America. Clinical Infectious Diseases : An Official Publication of the Infectious Diseases Society of America, 59(2), 147-159.

 

  1. Spelman, D., Baddour, LM. (2020). Cellulitis and skin abscess in adults: treatment. In: UpToDate, Post TW (Ed), UpToDate, Waltham, MA. Retrieved November 11, 2020. From: https://www.uptodate.com/contents/cellulitis-and-skin-abscess-in-adults-treatment?search=abscess%20treatment&topicRef=110529&source=see_link

 

  1. Russell, F., Rutz, M., Rood, L., Mcgee, J., & Sarmiento, E. (2020). Abscess Size and Depth on Ultrasound and Association with Treatment Failure without Drainage. The Western Journal of Emergency Medicine, 21(2), 336-342.

 

  1. Gaspari, R., Sanseverino, A., & Gleeson, T. (2019). Abscess Incision and Drainage With or Without Ultrasonography: A Randomized Controlled Trial. Annals of Emergency Medicine, 73(1), 1-7.

 

  1. Thornton J, Hellmich T. Evaluation and Management of Abscesses in the Emergency Department. Emergency Medicine Reports. 2017 May 1;38(10).
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