Approach to skin and soft tissue infections: Clinical sciences

Skin and soft tissue infections, or SSTIs for short, are infections that affect the skin and the underlying soft tissues like the fat, fascia, muscles, ligaments, and tendons. They are typically caused by bacteria, but can also occur from viruses or fungi.

In severe cases, these infections can cause life-threatening complications like necrotizing fasciitis and toxic shock syndrome that can quickly lead to septic shock; so, timely diagnosis is key to treat these infections promptly to prevent major complications.

When a patient presents with a chief concern suggesting a skin and soft tissue infection, your first step is to perform an ABCDE assessment to determine if they are stable or unstable. If the patient is unstable, stabilize their airway, breathing, and circulation right away. Establish IV access and start IV fluids for resuscitation. You should also obtain blood and wound cultures, and then initiate broad spectrum IV antibiotics.

Make sure to continuously monitor vitals like pulse oximetry, blood pressure, and heart rate as the patient’s condition can quickly deteriorate and require admission to the ICU.

Once you’ve initiated acute management, your next step is to obtain a focused history and physical examination. Additionally, order labs like CBC, CMP, lactate, and check the previously obtained blood and wound cultures. Typically, unstable patients will have a history of fever and severe pain around the affected area. On exam, you might find signs of shock like altered mental status, tachycardia, or hypotension.

Local examination will reveal erythema, edema and sometimes an associated rash. On palpation, the affected area will be tender with crepitus in severe cases. Crepitus feels like a crunching of small air pockets underneath the skin, and is a red flag for necrotizing soft tissue infection! In addition, you might see bullae, grayish or dark discoloration, and purulent drainage which is indicative of necrotic tissue.

Now, labs will typically reveal leukocytosis, electrolyte abnormalities, and elevated serum lactate. In most cases, blood and wound cultures will be positive. If these are your findings, consider a life threatening SSTI. Now, if your patient has been stabilized and you are concerned for a deeper infection, your next step is to obtain a CT scan of the affected area.

CT might reveal fat stranding, inflammatory changes or gas bubbles within the deep tissue layers. These characteristics strongly support your diagnosis of life-threatening SSTI such as necrotizing fasciitis, toxic shock syndrome, and gas gangrene.

Here’s a clinical pearl! Crepitus and pockets of gas along the fascia are strongly diagnostic of necrotizing fasciitis, which is a surgical emergency. Patients need to be taken to the operating room emergently for debridement of the necrotic tissue and washout. Any delay in treatment can quickly lead to death.

Alright, now that unstable patients are taken care of, let's switch gears and talk about the stable ones. For stable patients, your first step is to obtain a focused history and physical exam. Here, your goal is to differentiate between a purulent lesion and a non-purulent lesion. Lets begin with purulent lesions.

On history, your patient will typically report fever, malaise, and a lump with drainage; and they may have a history of diabetes mellitus. Keep in mind that patients with a history of diabetes with suboptimal glucose control are at a high risk of developing this kind of infection.

Expect your exam to reveal erythema, edema, and tenderness around a fluctuating mass containing pus. With these findings, consider a purulent lesion.

Okay, let's begin with the most common type of purulent lesion, a subcutaneous abscess, which is a walled off collection of pus underneath the skin. These occur when bacteria seeds within the soft tissue through a cut in the skin. Patients typically report focal swelling with pain, and they might notice murky, malodorous drainage. On exam, you can expect to see erythema, tenderness, and induration around a fluctuant mass with purulent drainage. With these findings, you’re dealing with a subcutaneous abscess.

Alright, let's talk about another type of purulent SSTI called hidradenitis suppurativa. This is a chronic condition where painful, inflamed nodules or abscesses form in the subcutaneous tissues of the hairy areas or skin folds where there is constant rubbing.

Patients usually report painful lumps around the axilla, groin, and inframammary area. Your patient might have risk factors like cigarette smoking or obesity. Exam typically shows multiple tender, erythematous nodules sometimes with visible sinus tracts and drainage. These findings support your diagnosis of hidradenitis suppurativa.

Moving on to our last type of purulent lesion, let’s discuss folliculitis, furuncles, and carbuncles. Folliculitis is an infection of the hair follicle; furuncles are a collection of folliculitis; and carbuncles are a cluster of furuncles.