What is the unifying diagnosis for a patient with left eyelid swelling, mild pain on extraocular movement, chemosis, and conjunctival injection in the left eye?

Orbital Cellulitis

The unifying diagnosis for left eyelid swelling, mild pain on extraocular movement, chemosis, and conjunctival injection is most likely orbital cellulitis, which requires immediate assessment and urgent ophthalmology consultation to prevent vision-threatening complications including cavernous sinus thrombosis, abscess formation, and permanent vision loss. 1, 2

Critical Distinguishing Features

The presence of pain on extraocular movement is the key distinguishing feature that elevates this presentation beyond simple conjunctivitis to orbital involvement. 1, 3 This combination of findings—eyelid swelling, chemosis, conjunctival injection, and painful eye movements—represents the classic tetrad of orbital cellulitis. 2, 4

Why This Is Orbital Cellulitis and Not Conjunctivitis

While viral conjunctivitis can present with eyelid swelling, chemosis, and conjunctival injection 5, it typically does not cause pain with extraocular movements. 5 The American Academy of Ophthalmology specifically identifies painful eye movements as a red flag requiring immediate assessment for orbital cellulitis. 1

Immediate Assessment Required

You must immediately evaluate for:

• Proptosis (forward displacement of the globe) 1, 2
• Degree of extraocular movement restriction and severity of pain with movement 1, 3
• Visual acuity changes or decreased vision 1
• Fever or systemic toxicity 1
• Corneal involvement using fluorescein staining (mandatory in every case) 1
• Pupillary examination for afferent pupillary defect suggesting optic nerve involvement 1

Differential Diagnoses to Consider

Orbital Pseudotumor (Idiopathic Orbital Inflammation)

This can mimic orbital cellulitis with identical presentation including eyelid swelling, chemosis, conjunctival injection, and painful extraocular movements. 3, 4 The key difference is that orbital pseudotumor responds dramatically to corticosteroids within 48 hours, whereas orbital cellulitis requires antibiotics and corticosteroids are contraindicated. 4 CT imaging showing inflammation of sclera, optic nerve, muscle, and orbital adipose tissue without abscess formation suggests pseudotumor. 3

Orbital Myositis

A subtype of orbital inflammatory syndrome presenting with identical symptoms: eyelid swelling, chemosis, pain, and restrictive paresis causing diplopia. 4 This also responds to corticosteroids rather than antibiotics. 4 CT reveals fusiform inflammatory enlargement of specific extraocular muscles. 4

Dacryoadenitis

Lacrimal gland inflammation can cause upper eyelid swelling, chemosis, and ocular motility restriction. 6 However, this typically presents with purulent discharge from lacrimal ductules and epiphora, which helps distinguish it. 6

Severe Adenoviral Conjunctivitis

Can present with eyelid swelling, chemosis, and conjunctival injection that "can resemble orbital cellulitis on exam." 5 However, adenoviral conjunctivitis produces watery discharge, follicular reaction, and preauricular lymphadenopathy without true pain on extraocular movement. 5

Life-Threatening Complications

Orbital cellulitis can rapidly progress to:

• Cavernous sinus thrombosis with bilateral involvement, cranial nerve palsies, and altered mental status 2
• Subperiosteal or orbital abscess requiring surgical drainage 1
• Septic pulmonary embolism 2
• Meningitis and septicemia 2
• Permanent vision loss from optic nerve compression 1

Immediate Management Algorithm

If any red flags present (proptosis, moderate-to-severe pain, vision changes, fever):

1. Emergent hospitalization with IV antibiotics (broad-spectrum coverage including MRSA) 1
2. Urgent ophthalmology consultation within hours 1
3. Contrast-enhanced CT of orbits and sinuses to identify abscess or sinus source 1, 2
4. Blood cultures if systemic toxicity present 2

If mild presentation without red flags:

1. High-dose oral amoxicillin-clavulanate 1
2. Mandatory daily follow-up until definite improvement 1
3. Hospitalization for IV antibiotics if no improvement in 24-48 hours or progressive infection 1

Common Pitfall

The most dangerous pitfall is misdiagnosing orbital cellulitis as viral conjunctivitis and sending the patient home with reassurance. 5, 1 While adenoviral conjunctivitis can "resemble orbital cellulitis on exam" with eyelid swelling and chemosis 5, any pain with extraocular movement mandates ruling out orbital cellulitis first. 1