AssessmentsSkin and soft tissue infections: Clinical practice
USMLE® Step 2 style questions USMLE
A 10-year-old boy comes to the emergency department with progressive right periorbital swelling for the past two days. He also complains of fever, nasal congestion, and blurry vision. On physical examination, his right eye is swollen closed. He also has proptosis, conjunctival injection, and is unable to abduct his right eye. The left eye is normal. Which of the following is the most likely diagnosis in this patient?
Content Reviewers:Rishi Desai, MD, MPH
Focal skin and soft tissue infections are often due to bacteria infections, and include conditions like impetigo, folliculitis, cellulitis, erysipelas, furuncles and carbuncles, and necrotizing fasciitis.
The first step is getting a full history.
Most skin infections tend to be localized and around a particular anatomic structure.
Some individuals have had contact with other individuals with skin infections, and this is commonly the case with community-acquired methicillin-resistant S. aureus, which causes cellulitis and furuncles.
Additionally, there may be adenopathy, which can occur in non-bullous impetigo and cellulitis, bullae which can be seen in bullous impetigo, and crepitus with edema that exceeds the rash border, which can be seen in necrotizing fasciitis.
Additional labwork should be done when there are signs and symptoms of systemic toxicity.
Blood cultures are unlikely to be positive in simple localized infections like impetigo and folliculitis, but should be taken when there’s deep tissue involvement like necrotizing fasciitis or erysipelas.
Other tests include a CBC, C-reactive protein level, and liver and kidney function tests.
An x-ray can be done when there’s a deep infection and bone involvement is suspected.
In necrotizing fasciitis, a CT scan is often done as well, although diagnosis is always made through exploratory surgery.
Head CT scans are specifically helpful in orbital cellulitis, which can cause neurological deficits, proptosis or protrusion of the eyeball, deteriorating vision, bilateral ocular edema or ophthalmoplegia with diplopia.
Finally a skin biopsy isn’t routine but can be done when other tests are inconclusive, often to look for non-infectious causes.
In non-bullous impetigo, the lesions develop on previously damaged skin by things like insect bites or abrasions, and they start as vesicles or pustules which evolve over about a week into gold-crusted plaques, that are often about 2 centimeters in diameter.
Some are pruritic and there may be regional adenopathy.
The lesions usually affect the face and extremities and heal without scarring.
Bullous impetigo is characterized by flaccid, fluid-filled vesicles and blisters or bullae.
These are painful, spread rapidly, and there are usually systemic symptoms like fever, chills, and malaise.
There are usually multiple lesions, particularly around the nose and mouth, buttocks and trunk, and in body folds.
The bullae rupture easily, leaving a rim of dry skin that surrounds a shallow wet erosion.
Empiric topical treatment is usually given and common choices include mupirocin, applied three times daily and retapamulin, applied twice daily, both for five days.
Usually multiple lesions develop anywhere there’s hair, like the scalp, arm pit, or groin area.
Other symptoms include pruritus or tenderness, and the pustules tend to heal without any scarring or follicle loss.
A gram stain and culture should be done to identify the causative organism.
Treatment is not always necessary because mild folliculitis with few pustules often resolves spontaneously.
In cellulitis the margins are hardly noticeable because the process is deep underneath the skin.
Adenopathy and symptoms like fever and chills are common.
Although cellulitis occurs mostly on the extremities, it’s particularly worrisome when it affects the eyes.
Generally speaking, cellulitis can also be worrisome if it extends into deeper structures - it can lead to thrombophlebitis, osteomyelitis, and septic arthritis - as well as the development of an abscess.
Additional tests are recommended when the individual is febrile and appears toxic.