Superficial Abs..

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?

#### Superficial Abscess

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:

1. 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.

1. Size and depth: If there is concern about how big and/or deep the ...

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