Eric N. Feins, MD
A 37-year-old man presents to the emergency department complaining of a painful bulge over his left forearm. He states that he noticed some redness around the area 1 week ago, and then over the past few days it has become more swollen and painful, but it has not drained anything. He denies fevers, but thinks he’s had some occasional chills. He has no other medical problems and denies injecting drugs.
On physical exam, he is afebrile, HR 95, and BP 115/75. He has overall good hygiene and is well kempt. Over the dorsolateral aspect of his left forearm there is a 3-cm erythematous, fluctuant mass. It is extremely tender to light palpation and is mobile. Nothing can be expressed from the mass on palpation. There is also a 4- to 5-cm margin of erythema surrounding the mass without any evidence of streaking up the arm.
1. What, if any, additional imaging would you obtain?
2. Can you drain this abscess in the ED, or should it be done in the OR?
3. Is antibiotic therapy warranted for this patient?
Not all superficial abscesses are created equal and host factors often explain their etiology and severity. Superficial abscesses can arise in otherwise healthy individuals who develop skin breakdown (ie, abrasion, cut, surgical incision) that allows the entry of pathogenic bacteria. These are typically simpler to manage because the patient lacks risk factors and is immunocompetent. In contrast, patients with a history of injection drug use are at risk for recurrent superficial infections and abscesses. Immunocompromised patients (ie, diabetics) are also at risk for developing more severe infections due to their impaired host defenses.
Host factors influence the microbiology of superficial abscesses. Simple abscesses in immunocompetent patients are typically due to skin flora: Staphylococcus and Streptococcus, although gram-negative and anaerobic bacteria, can be involved. Methicillin-resistant Staphylococcus aureus (MRSA) is becoming increasingly common in some regions and is particularly prevalent in recently hospitalized patients, injection drug users, and diabetics. Pseudomonas aeruginosa is common in diabetics with abscesses (often on the feet), and is quite virulent if not treated. This is important to consider if antibiotics will be prescribed (see below).
1. A bedside ultrasound can be a useful adjunctive test. Ultrasound will give you 3 important pieces of information:
A. Whether there really is a drainable collection: It can sometimes be difficult to determine on physical exam if an abscess is actually present, or if you are just feeling inflamed tissue from a cellulitis (ie, induration). Both cellulitis and abscesses will have warmth, redness, and tenderness (general markers of inflammation), and some abscesses will not have obvious fluctuance. In these cases of uncertainty ultrasound can confirm/rule out the presence of an abscess that needs drainage.
B. Size and depth: If there is concern about how big and/or deep the abscess is, an ultrasound will help. This is important if you are concerned the abscess is so big or deep that it requires incision and drainage (I&D) in the OR.
C. Surrounding structures: Sometimes abscesses are located near important structures (ie, blood vessels). In these cases, ultrasound can help you avoid such structures during a drainage procedure.
For this particular patient with these physical findings ultrasound would not be necessary because it is clear that there is an undrained abscess, and it is not big enough or deep enough to require I&D in the OR.
2. This patient requires formal I&D of his undrained abscess under local anesthesia in the ER. This represents “source control,” which is an important principle for the treatment of infections.
In some cases it is more appropriate to drain a superficial abscess in the OR. The following are relative contraindications to a bedside I&D of a superficial abscess:
A. Size/depth: There is no fixed size cutoff, but generally, abscesses that are too large or too deep to anesthetize with local anesthesia and/or require an extensive debridement should be done in the OR.
B. Location: Abscesses in sensitive locations may require I&D in the OR due to the need for sedation or general anesthesia. In particular, this includes perirectal abscesses. While some are superficial enough to drain under local anesthesia, many are deeper and close to critical structures (ie, anal sphincter). These often require general anesthesia for patient comfort, to attain adequate exposure, and to evaluate for fistulae.
C. Patient anxiety or pain tolerance: Some patients cannot tolerate bedside drainage, due to either their expected intolerance of pain or their baseline anxiety about the procedure. The operating room is the appropriate place for these patients as it allows for improved analgesia and optimal conditions to minimize procedure length.
Adequate drainage of an abscess requires several important components:
A. Incision: Your incision must be large enough to ensure adequate drainage. The incision need not extend over the entire length/diameter of the abscess, although if in doubt, you should err on the side of larger. There is no hard rule for incision size, but as an example, a 3-cm abscess might be adequately drained with a 2- or 3-cm incision.
B. Deloculation: After opening the cavity, gentle exploration with a cotton-tipped probe and curved hemostat (clamp) is necessary to break up any loculations within the cavity. The patient may require additional deep injection of local anesthetic.
C. Packing: After initial drainage the cavity must be kept open to allow for further drainage of leftover fluid/debris. This involves loosely packing the cavity with 0.25- or 0.5-in wide packing ribbon. Insert enough to keep the cavity open, and leave the ribbon extending out of the skin to prevent the skin edges from closing. Premature skin closure can lead to abscess recurrence. The abscess will heal by secondary intention.
Sending a wound culture is always a good idea. If the patient has a soft tissue infection (ie, cellulitis) in addition to an abscess, the culture data can help you narrow the initial empiric treatment. While patients without soft tissue infection will usually improve with drainage alone, if the patient later develops worsening soft tissue infection, then antibiotic therapy could be started and directed toward the culture data.
3. The 2 main determinants of whether antibiotic therapy is warranted are: (A) presence of surrounding soft tissue infection and (B) host-related factors.
A. Presence of soft tissue infection: Cellulitis, the most common form of soft tissue infections associated with superficial abscesses, requires treatment with antibiotics. In the patient presented here, there is a significant degree of surrounding erythema/tenderness consistent with cellulitis. Therefore, he will require antibiotic therapy. In many cases, abscesses do not have significant surrounding erythema, warmth, or redness, suggesting absence of cellulitis. In these cases, antibiotics are not warranted.
B. Host-related factors: In immunocompetent patients there is no need for antibiotics after abscess drainage, assuming there is no surrounding cellulitis. For them, we rely on their immune defenses to completely eradicate the infection after drainage. However, in immunocompromised patients (ie, diabetics) it is reasonable to consider a short course of antibiotics, and this can be discussed with a senior resident.
Antibiotic choice: For the immunocompetent host with a simple, drained abscess and surrounding cellulitis, empiric coverage with an oral β-lactam antibiotic is appropriate to cover staphylococcal and streptococcal organisms: dicloxacillin or cephalexin (even if penicillin-allergic but without any immediate hyper-sensitivity reaction). If there is concern for MRSA (see above) or the patient has an allergy to penicillin, alternative oral antibiotic option is clindamycin or TMP-SMZ.
Patients with extensive, severe cellulitis and signs of systemic toxicity (ie, fevers, abnormal vital signs, etc) should receive parenteral antibiotics that cover MRSA as well as gram-negative and anaerobic bacteria. Two typical antibiotic regimens are:
• Vancomycin (MRSA coverage), and
• Piperacillin–tazobactam or ticarcillin–clavulanate (gram-negative+anaerobic coverage)
• Vancomycin (MRSA coverage), and
• Ceftriaxone or ciprofloxacin (gram-negative coverage), and
• Metronidazole (anaerobic coverage)
Diabetics often have more severe soft tissue infections involving Pseudomonas. These typically require treatment with an antipseudomonal antibiotic, such as piperacillin–tazobactam or cefepime.
The patient presented here has significant surrounding cellulitis that is concerning, although he has no systemic signs of infection. A reasonable treatment plan after I&D is to start an oral antibiotic (dicloxacillin or cephalexin) and admit the patient for 12 to 24 hours to ensure improvement of the cellulitis after a day of antibiotic treatment.
TIPS TO REMEMBER
Bedside ultrasound is a useful modality for both diagnosis and procedural planning.
The length of the incision for an abscess can vary but should be large enough to ensure adequate drainage.
After incision, adequate drainage requires you to break up the loculations and loosely pack the cavity with gauze or other packing material.
Assuming an abscess is adequately drained, the main indications for antibiotic therapy are: (1) presence of surrounding cellulitis, (2) severe infection with systemic signs of illness, or (3) patient immunocompromise (eg, from diabetes).
1. To ensure adequate drainage of a superficial abscess, which of the following is/are important component(s)? (Choose all that apply.)
A. Skin incision large enough to ensure adequate drainage
B. Deloculation of abscess cavity
C. Antibiotic treatment
D. Loose packing
2. Which of the following are contraindications to I&D of a superficial abscess under local anesthesia? (Choose all that apply.)
A. Immunocompromised patient
B. History of injection drug use
C. Large size
D. Sensitive location
E. Location requiring extensive exposure
1. A, B, D. Antibiotic treatment is most important for treatment of surrounding cellulitis, not for drainage of an abscess.
2. C, D, E. Immunocompetency and history of drug use are risk factors for more severe infection, but do not preclude drainage of the abscess under local anesthesia.