Medical Concepts: Diabetic Foot Infections

In Medical Concepts by Alia Dharamsi2 Comments

Editor’s note: In this post we are going back to some BoringEM basic content, a case-based approach to classifying diabetic foot infections. It is designed to follow the introductory Chalk Talk: An approach to skin infections, available HERE. This awesome series was created by Alia Dharamsi (@alia_dh) a PGY1 in EM at the University of Toronto. 

A fantastic quick reference pocket card is available for download.  Click on the picture or link below.

Screenshot 2015-04-11 14.00.17

Diabetic Foot Reference Card

Objectives

  1. Classify diabetic foot infections into uninfected, mild, moderate, severe
  2. Name the most likely pathogens causing diabetic foot infections of varying severity
  3. Prescribe an antibiotic regimen for mild, moderate, severe diabetic foot infections

 

The Cases

Case 1 (Click to reveal case)

You are working in an urban ED when Unna, a 55 year old female, presents to the ED to ask about a lesion that her husband found on the bottom of her right foot yesterday.

History

It has never been painful, there is no warmth to the area, erythema, or any purulent drainage. She has no fever or chills. Her foot is mostly insensate secondary to a 20 year history of diabetes, which is poorly controlled (on insulin, sugars range from 10-20 on any given day).

  • PMHx: diabetes mellitus type 2
  • Medicationsinsulin, metformin, ramipril, rosuvastatin, pantoprazole
  • Allergies: none
  • Social History1 PPD smoking, social alcohol consumption (2 drinks/month), no drug use, works as a mail clerk in an office building

Exam

BP 132/86, HR 78, RR 14, O2 98% RA, Temp 36.7

1×1 cm ulcer on the plantar aspect of the heel of her left foot. There is no ulceration, drainage, erythema, or rubor (warmth)Her peripheral pulses are present, but she has decreased sensitivity to light touch and pinprick on her R and L soles.

Questions

1. How would you classify this ulcer in terms of severity? (Click to reveal answer)

Since this ulcer is not showing any local signs of infection, there is no history of purulent drainage, and there is no sign of deeper involvement to bone or soft tissue, this ulcer is uninfected. 

2. Does Unna require antibiotics at this time? (click to reveal answer)

No. Uninfected ulcers do not require antibiotics

Management

  • In the emergency department: Since this wound is not infected, and she is not systemically unwell, she does not require hospital admission. You decide to discharge her home: recommend reduced weight bearing and elevating foot to facilitate healing follow up with family doctor for assessment of the wound.
  • Referrals: Diabetic foot care team for coordinated management: she will need to have the wound re checked, as well as peripheral vascular assessments, and possibly fitting for offloading boot. The fact that she is a smoker and has Diabetes puts her at increased risk of peripheral vascular disease. May also consider an endocrinology consult for closer monitoring of diabetes, and optimal management of complications. 

Case 2 (Click to reveal case)

Your next patient that night is Cam, a 68 year old obese male with pain in his left foot.

History

The area has been painful for quite some time, “probably weeks.” He has previously been seen by his GP for this problem, and has been told he has an “ulcer on the side of my foot.” He has never been on antibiotics for this problem. On history the area has a throbbing pain, although his feet are mostly insensate and have been for years. He thinks his foot feels warm to touch, and he noted that his socks have a green-yellow discharge on them from his foot. He is unable to see the soles of his feet due to osteoarthritis of his joints prohibiting appropriate flexion.

  • PMHx: Type 2 diabetes, CHF, HTN, OA, OSA, asthma
  • MedicationsInsulin, furosemide, metoprolol, atorvastatin, ramipril, atrovent, ventolin
  • Allergies: none
  • Social Hx: 1ppd smoking, social alcohol consumption (10/week), works occasionally for a contracting company

Exam

BP 134/72, HR 66, RR 14, O2 96% RA, Temp 36.9

There is a 2cm x 2cm ulcer on his left foot. The area is surrounded by 1-2 cm of cellulitis and erythema, and there is some discharge from the wound. You probe gently and do not detect any involvement to bone (and since you dont probe to bone you have a lower suspicion of osteomyelitis). His peripheral pulses are present, but he has decreased sensitivity to light touch and pinprick on his R and L soles.

Questions

1. How would you classify  Cam’s ulcer? (Click to reveal answer)

Cam’s foot ulcer is mild, and although there are local signs of infection, there does not seem to be any extension to bone or deeper soft tissue, and he is systemically well

Mild- 2 or more signs of inflammation (below) AND infection limited to skin and superficial dermis, with no local complications or systemic illness

  • purulent secretions
  • erythema <2cm
  • pain
  • tenderness
  • warmth
  • induration
2. Does Cam require antibiotics at this time? (Click to reveal answer)

Yes, he is beginning to show signs of local infection.

3. What microbes should you consider in the differential of his infection? (Click to reveal answer)

In mild diabetic foot infections, most likely causes are Streptococci, and Methicillin-Susceptible Staph Aureus.

4. Does Cam have risks for community acquired or hospital acquired methicillin resistant staphylococcus aureus infection? (Click to reveal answer)

Cam does have a risk factor for CA-MRSA but none for HA-MRSA. His diabetes should trigger you to think about CA-MRSA and should make turn to your local guidelines to determine the appropriate treatment. In Cam’s case, based on local antibiograms empiric coverage of MRSA is not recommended, and this is a first time DFI therefore empiric CA-MRSA coverage was not initiated. . The risk factors are:

  • Hospital acquired: hospitalization, long-term care, recent antibiotic therapy, hemodialysis
  • Community acquired*: HIV infection, men who have sex with men, injection drug use, unsanitary/cramped living conditions, incarceration, military service, sharing sports equipment,  diabetes

*avoid clindamycin if suspected CA-MRSA due to inducible resistance

5. What antibiotics are recommended for mild diabetic foot infections? (Click to reveal answer)

Mild infections, without MRSA Coverage, choose 1 of:

  • Cephalexin 500mg PO QID
  • Dicloxacillin 500mg PO QID
  • Amox-Clav 875/125mg PO BID
  • Levofloxacin 750mg PO Daily
  • Clindamycin 450mg PO TID

Mild infections, with MRSA coverage, choose 1 of

  • Clindamycin 450mg PO TID
    • Avoid Clindamycin in suspected CA-MRSA due to inducible resistance
  • Cephalexin OR Dicloxacillin WITH TMP/SMX (DS) 2 tabs PO BID
  • Cephalexin OR Dicloxacillin WITH Doxycycline 100mg PO BID

Duration of treatment for Mild DFIs is 7-14 days

Management

  • In the emergency department: You do not think that Cam requires admission at this time, and you plan to discharge him home.
    • You send a swab for C&S.
    • Since Cam does not have risk factors for CA-MRSA or HA-MRSA, you provide him with a prescription for antibiotics: Cephalexin 500mg PO QID x 14 days
    • Instructions for follow up with GP
    • Instructions to offload pressure to the area: an offloading boot is fitted for him
    • Home care nursing for dressing changes
  • Referrals: Wound care team is contacted for coordinated approach to diabetic foot ulcers. Will need peripheral vascular assessment, as well as close monitoring and possibly fitting for shoes that prevent excoriation of ulcerated area. Consider consulting endocrinology for diabetes management.

Case 3 (Click to reveal case)

Recall Cam, a 68 year old obese male with pain in his left foot who returns to your ED 4 months later.

History

He completed the previous round of antibiotics, and had complete resolution of the erythema and pain, as well as no purulent drainage for at least 2 months. This wound was initially healing but has been deteriorating for the past 6 weeks. Since his last visit to the ED he has been followed by Endocrinology, however has been non compliant with new insulin recommendations and a special shoe that he was fitted with by the wound care team. The area is now more painful, and he feels there is a pocket of fluid on the bottom of his foot that drains significant amounts of yellow-green pus.

  • PMHx: Type 2 diabetes (insulin), CHF, HTN, OA, OSA, asthma
  • Medications: Insulin, furosemide, metoprolol, tylenol arthritis, atrovent, ventolin
  • Allergies: none
  • Social Hx: 1PPD smoking, social alcohol consumption (10/week), unemployed due to foot pain

Exam

BP 138/86, HR 77, RR14, O2 95% RA, Temp 36.8

There is a 2cm x 2cm ulcer on the lateral aspect of his left foot. The area is surrounded by 4 cm of cellulitis and erythema, and there is significant discharge from the wound. There is a central area of fluctuance. You probe gently and do not see any involvement to bone. His peripheral pulses are present, but he has decreased sensitivity to light touch and pinprick on his R and L soles.

Labs and Imaging

Due to the significant appearance of this wound, you get labs and ask for an ultrasound of the foot to assess for a deeper infection as well as an Xray to assess for any osteomyelitis. Significant results:

  • WBC: 12.8 (elevated)
  • ESR: 8 (normal)
  • CRP: normal
  • U/S: 5x5x6cm  deep abscess extending from plantar fascia deep towards calcaneous
  • X-ray: no fractures or evidence of OM noted

Questions

1. How would you classify Cam’s ulcer now?  (Click to reveal answer)

Moderate diabetic foot infection. Cam’s ulcer has both evidence of deep tissue abscess, and significant cellulitis.

Moderate diabetic infections have at least 1 of:

  • cellulitis > 2 cm
  • spread beneath fascia (fasciitis)
  • deep tissue abscess
  • gangrene
  • osteomyelitis, septic arthritis, involvement of muscle
2. Does Cam require antibiotics? (Click to reveal answer)

Yes. Moderate infections require antibiotic treatment.

3. Which microbes should you consider in the differential of this infection? (Click to reveal answer)

In Moderate diabetic foot infections consider a broader differential, including Staph (MSSA AND MRSA), Streptococci., Enterobacter, Enterococcus, obligate anaerobes.

4. What antibiotics are recommended for moderate diabetic foot infections? (Click to reveal answer)

Moderate infections, if you do not suspect MRSA

  • Clindamycin 300-45 mg PO QID with a Fluoroqinolone like Levofloxacin 750mg PO q24h or Ciprofloxacin 750mg PO q12h
  • You can start also with IV Clindamycin 600-900mg q8h with an IV Fluoroquinolone, then step down to PO.

Moderate infections, if you suspect MRSA (avoid Clindamycin in suspected CA-MRSA due to the possibility of inducible resistance)

  • TMP/SMX 2 tabs PO BID + Amoxicillin-Clavulanate 875/125 PO BID x 2-4 weeks
  • Clindamycin 300-450mg q 6-8 hours WITH a Fluoroquinolone (egMoxifloxacin 400mg PO q24hours OR Levofloxacin 750 mg PO q 24hours OR Ciprofloxacin 750mg PO q12hours)

Duration of Treatment for Moderate DFIs is 2-4 weeks.

Management

  • In the emergency department: The abscess is complex and quite deep, and you do not feel that you would get adequate drainage with an ED I&D, and consider the need for surgical management. You consult orthopaedics, and they see him in the ED and perform an I&D. Orthopaedics agrees with your choice of antibiotics, and you write him a prescription for Levofloxacin and Clindamycin. He still does have the CA-MRSA risk factor of diabetes and although deceiving his antibiotic use does not qualify as a risk for HA-MRSA since he had complete resolution of his symptoms for > 2 months. So, as was the case above, based on local guidelines you determine MRSA coverage is not necessary. Follow-up in clinic is arranged, with the wound care team, and they will consider further operative I&D pending repeat ultrasound. A swab is sent to microbiology for C&S.
  • Referrals: You refer him back to Endocrinology, and ask him to follow up with his GP.

Case 4 (Click to reveal case)

What if Cam had presented to the ED with the exactly the story as Case 3 but showed systemic signs of infection including fever of 38.4 degrees, chills, and tachycardia (115 bpm)?

Questions

1. How do you classify his infection with respect to his new symptoms? (Click to reveal answer)

Cam now has a severe infection. Severe infection have evidence of local infection as in moderate, AND signs of systemic toxicity (SIRS), i.e. at least 1 of

  • Temp >38 or <36
  • Pulse >90bpm
  • Tachypnea >20 breaths/minute or PaCO2< 32
  • WBC >12 or <4, or >10% bands
2. Does Cam require antibiotics? (Click to reveal answer)

Yes, severe infections require antibiotic treatment

3. Which microbes should you consider in the differential of this infection? (Click to reveal answer)

In severe diabetic foot  infections consider a broader differential, including Staph (MSSA AND MRSA), Streptococci, Enterobacter, Enterococcus, obligate anaerobes.

4. What antibiotics are recommended for severe diabetic foot infections? (Click to reveal answer)

Severe infections with no MRSA risk factors

  • Moxifloxacin 400mg IV q24 hours
  • Ertapenem 1gm IV q24 hours
  • Imipenem-cilastatin 500mg IV q6 hours
  • Pip/tazo 4.5g IV q8 hours

Severe infections, with MRSA risk factors or high clinical suspicion for MRSA, ADD

  • Linezolid 600mg PO q12 hours
  • Daptomycin 4-6mg/kg IV q24 hours
  • Vancomycin 15-20mg/kg IV BID

Duration of Treatment for Severe DFIs depends on symptomatology. Monitor patient and step down to PO antibiotics as soon as clinically indicated.

 References

1. Gemechu, Fassil W., Fnu Seemant, and Catherine A. Curley. “Diabetic foot infections.” American family physician 88.3 (2013): 177-184.

2. Lipsky, Benjamin A., et al. “2012 Infectious Diseases Society of America clinical practice guideline for the diagnosis and treatment of diabetic foot infections.” Clinical infectious diseases 54.12 (2012): e132-e173.

3. Lipsky, B., Berendt, A., Cornia, P., Pile, J., Peters, E., & Armstrong, D. et al. Executive Summary: 2012 Infectious Diseases Society of America Clinical Practice Guideline for the Diagnosis and Treatment of Diabetic Foot Infections. Clinical Infectious Diseases54(12), (2012): 1679-1684. doi:10.1093/cid/cis460

4. Weintrob, A., Sexton, D., (2014). Clinical manifestations, diagnosis, and management of diabetic infections of the lower extremities. Retrieved 31 December 2014, from uptodate.

This piece was created as part of a joint Digital Scholarship Elective between the University of Toronto and McMaster University.  This piece has been reviewed for content by Drs. Andrew Petrosoniak and Teresa Chan.  The piece was peer reviewed by (soon-to-be-Dr.) Eve Purdy

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Alia Dharamsi

Alia Dharamsi

Alia Dharamsi is an Emergency Physician at the UHN and St Michael’s Hospital in Toronto. Her interests include simulation, prehospital medicine, and educational innovation. In her spare time you can find her on her bike, in the lake, or on a mountain!
Alia Dharamsi
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BoringEM
BoringEM has been 'bringing the boring' to emergency medicine since 2012. In 2016 this Canadian blog brought its content to CanadiEM.
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