Abscess Obsession: An Evidence-based Guide to Treating an Abscess

Physicians have been making the diagnosis of abscesses clinically since the birth of the profession. However, recent studies have found that the inter-rater reliability of the clinical exam to be quite low. One study found a kappa of only 0.48 for abscess presence and 0.43 for whether the abscess would require drainage;^[1] a second study had similar findings at 0.39 and 0.43, respectively.^[2] These numbers aren’t great. And, because draining an abscess in a young child is likely going to require either conscious sedation or an armada of medical providers armed with a papoose, it’s not something you want to misdiagnose and attempt to drain unnecessarily.

Fortunately, the age of ultrasound has given us a tool that can aid us in our diagnosis. A recent review done in our own PEM department pooled six studies comparing physical exam alone with exam with ultrasound for the diagnosis of soft-tissue abscesses. It found that exam alone had a sensitivity of 75-95% and a specificity of 60-84%; supplementing exam with ultrasound showed a modest improvement of 90-98% sensitivity and 67-88% specificity. All studies used the diagnostic gold standard of purulent fluid drainage on initial incision or at follow-up^[3].

It’s easy, quick, and likely to decrease your need for torturing a small child, so why not throw a probe on it before grabbing the knife?

It seems intuitive that using a needle to drain the pus out of an abscess might be less painful, leave a smaller scar, and perhaps require less sedation than incision and drainage. In reality, though, is it as effective?

The above type of aspiration is out of the scope of practice in the emergency room.

A recent RCT on approximately 101 patients allocated abscesses requiring drainage to either aspiration or traditional incision. Demographics in both groups were comparable. The patients were then followed on days 0, 2 and 7 for these outcomes: 1) resolution or 2) necessity for additional intervention.^[4] In the aspiration group, investigators visualized the needle entering the pocket by ultrasonography. In both groups, abscess resolution post-intervention was assessed using ultrasound. The investigators found that at day 2 and 7, incision and drainage showed no difference to aspiration. However, 60% of those who received aspiration failed to show complete drainage on ultrasound immediately post-procedure and required escalation to full incision and drainage.

So – if the initial aspiration works, it may be as good as an I & D. However, if it doesn’t work, it will just prolong the process. I’d personally be inclined to just reach for the scalpel, but the opportunity is there for having an open discussion with the patient/guardian regarding both procedures.

For really gnarly I & D, see above.

In or out?

So, you’ve drained your pocket of pus. Do you pack it? If you really think about it, it makes sense not to – isn’t that cloth you’re shoving into the recently infected hole a potential nidus for infection? Also, you’re taking the irritated skin that you just subjected to violation with a scalpel and then just poked several times with a hemostat, and now you’re going to jam some lightly lubricated cloth into that hole right against their fresh wound. Also, they then have to come back and get it removed. All of this is painful.

An RCT of 49 patients randomized to receive packing or
no packing and followed at 48 hours and at 10 days found no difference in treatment failure,^[5] although both groups had a relatively high rate of re-instrumentation (70% of those in the packing group and 59% in the group that was not packed). Secondary outcomes of pain score, patient satisfaction and patient-rated cosmesis were also not significantly different. A second study of 48 patients found no difference in treatment success between those receiving packing or no packing, but did find that those receiving packing reported more pain immediately post-procedure and at 48 hours.^[6]

These are both small studies, but they are in agreement that packing may be an unnecessary, painful step.

Antibiotic resistance is a problem. Can we cut down on using antibiotics in patients that have undergone I & D?

A recent study published in NEJM this year randomized more than 1,000 patients that had received I & D to trimethoprim-sulfamethoxazole or placebo and followed them at 7 and 14 days for clinical cure rates. Investigators found a cure rate of 86.5% in those prescribed trimethoprim-sulfamethoxazole and 74.3% for placebo; this was non-significant.^[7] This study is in agreement with previous, smaller investigations that drew the same conclusion.^[8],[9],[10]

The caveat here is that all of these studies excluded patients with abscesses that were complicated in any way – surrounding cellulitis, immunocompromised (including diabetics), or if the abscess was located on the hands, face or genitals. Additionally, most had an exclusion criteria clause that basically allowed investigators to say “eh, this looks bad, let’s not include them in the trial.”

Eh, let’s not include this one in the trial.

So, the conclusion here? There’s some suggestion that trimethoprim-sulfamethoxazole may be helpful if the patient has MRSA, although there’s no way to know what’s in that pocket ahead of time. There’s probably no benefit in prescribing antibiotics in healthy patients with uncomplicated abscesses that have been drained. Immunocompromised patients, surrounding cellulitis, or abscesses in difficult-to-drain locations remain to be studied.

These data are essentially in agreement with the IDSA 2014 guidelines, which suggest antibiotics for ‘severe or extensive disease,’ abscesses in the presence of cellulitis, signs of systemic illness, immunosuppression, abscesses in difficult-to-drain locations, septic phlebitis, or in extremes of age^[11].

But what if there was a better way? What if we didn’t even have to violate this poor child’s skin at all?

It’s possible that topical anesthetic cream may aid in spontaneous drainage. There’s only been one study on this concept thus far, in which a group evaluated a cohort of 300 patients that presented with abscesses.^[12] This department placed topical anesthetic on just over half of patients with abscesses, and found that spontaneous drainage occurred in about a quarter of those in which anesthetic was applied. Importantly, those receiving the topical anesthetic were significantly less likely to require procedural sedation.

This study has obvious methodological issues, but I would argue it’s still worth a shot, as it’s cheap, easy, and even if it’s ineffective at popping the abscess it’ll at least help with the notoriously difficult analgesia required for incision and drainage.

• Ultrasound – Why not?
• Aspiration is effective, but has a high rate of conversion to traditional incision and drainage, thereby prolonging the process
• Packing after drainage is painful and may not be warranted
• The IDSA guidelines are consistent with the evidence we have – antibiotics for simple abscesses in the immunocompetent patient aren’t required
• Try some topical anesthetic, it might mitigate the need for a procedural sedation