A 6-year-old boy is brought to the clinic by his father due to a 24-hour history of left e… — USMLE Step 2 CK

A $6$ -year-old boy is brought to the clinic by his father due to a $24$ -hour history of left eye redness and swelling. The father reports that the child sustained a mosquito bite near his left eyebrow $3$ days ago. Yesterday, the area became red, and this morning his eye was swollen shut. The boy has been eating and drinking normally and has had no rhinorrhea or sinus pain. Temperature is $37.6^\circ\text{C}$ ( $99.7^\circ\text{F}$ ), heart rate is $98/\text{min}$ , respiratory rate is $20/\text{min}$ , and blood pressure is $100/65\text{ mmHg}$ . On physical examination, the left upper and lower eyelids are severely edematous, warm, and erythematous, preventing the patient from opening the eye spontaneously. With gentle manual retraction of the eyelids, the sclera and conjunctiva appear clear without chemosis. The pupils are equal, round, and reactive to light. Visual acuity is $20/20$ in both eyes. Extraocular movements are fully intact in all directions, and the patient denies pain with eye movement. There is no proptosis. Which of the following is the most appropriate next step in the management of this patient?

A
Admit for intravenous vancomycin and ceftriaxone therapy
B
Obtain a computed tomography scan of the orbits and sinuses
Prescribe oral clindamycin and arrange close outpatient follow-upAnswer
D
Apply topical erythromycin ophthalmic ointment
E
Administer intravenous acyclovir

Answer

Prescribe oral clindamycin and arrange close outpatient follow-up

This patient has preseptal (periorbital) cellulitis, an infection of the tissues anterior to the orbital septum. It typically arises from contiguous spread of a local skin infection, such as an insect bite or minor trauma. The hallmark of preseptal cellulitis is eyelid erythema and edema. Importantly, while the swelling can be severe enough to force the eye closed, the infection does not involve the structures posterior to the orbital septum. Because the physician was able to gently retract the eyelids and confirm the absence of proptosis, normal visual acuity, and intact extraocular movements without pain, orbital cellulitis is effectively ruled out.

Therefore, outpatient management with oral antibiotics that cover *Staphylococcus aureus* (including MRSA) and *Streptococcus pyogenes*, such as oral clindamycin, is the most appropriate next step.

Feature	Preseptal Cellulitis	Orbital Cellulitis
Infection Site	Anterior to orbital septum	Posterior to orbital septum
Eyelid Swelling/Erythema	Present	Present
Eye Pain with Movement	Absent	Present
Proptosis (Bulging)	Absent	Present
Decreased Visual Acuity	Absent	Often Present
Management	Outpatient oral antibiotics	Inpatient IV antibiotics $\pm$ surgery

Step-by-Step Solution

Analyze the clinical presentation and physical exam findings.

The patient has severe eyelid edema and erythema following a bug bite, but a completely normal globe exam (no proptosis, normal extraocular movements, no pain with movement).

Differentiating between preseptal and orbital cellulitis is the critical first step in determining management.

Establish the diagnosis based on the presence or absence of orbital signs.

The absence of orbital signs definitively points to preseptal (periorbital) cellulitis, despite the severity of the eyelid swelling.

Orbital cellulitis involves structures posterior to the orbital septum and typically causes proptosis, ophthalmoplegia, and pain with eye movement.

Select the appropriate therapeutic intervention.

Uncomplicated preseptal cellulitis is managed in the outpatient setting with oral antibiotics (e.g., clindamycin) covering common skin flora.

Intravenous antibiotics or advanced imaging are reserved for orbital cellulitis or complicated preseptal cellulitis where the eye cannot be physically examined.

Key Concept

Preseptal cellulitis can be distinguished from orbital cellulitis by the absence of proptosis, ophthalmoplegia, and pain with eye movement. It is safely treated with oral antibiotics in the outpatient setting.

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