What diseases are commonly mistaken for preorbital cellulitis in children?

Diseases Commonly Mistaken for Preseptal (Periorbital) Cellulitis in Children

The most critical condition to differentiate from preseptal cellulitis is orbital (postseptal) cellulitis, which requires immediate hospitalization with IV antibiotics due to risk of vision loss and life-threatening complications including cavernous sinus thrombosis. 1, 2

Primary Differential Diagnoses

Orbital (Postseptal) Cellulitis

This is the most dangerous mimicker and must be ruled out immediately. The key distinguishing features include:

• Proptosis (forward displacement of the eyeball) 1, 2
• Impaired or painful extraocular movements 1, 2
• Ophthalmoplegia (paralysis of eye muscles) 1, 2
• Decreased visual acuity 1, 2
• Age >3 years with gross periorbital edema 1, 2

The American College of Radiology emphasizes that CT orbits with IV contrast should be obtained immediately if any of these orbital signs are present, as clinical examination alone is insufficient to distinguish between preseptal and postseptal involvement 1, 3. Failing to recognize orbital cellulitis can result in permanent vision loss, cavernous sinus thrombosis, meningitis, brain abscess, or death 1, 2.

Viral Conjunctivitis with Eyelid Swelling

Viral conjunctivitis, particularly epidemic keratoconjunctivitis, can present with:

• Eyelid swelling and erythema that mimics preseptal cellulitis 4
• Preauricular lymphadenopathy (a distinctive feature) 4
• Watery discharge rather than purulent discharge 4
• Follicular reaction of the inferior tarsal conjunctiva 4
• Bilateral involvement (often sequentially bilateral) 4

The presence of preauricular lymphadenopathy and watery discharge rather than purulent discharge helps distinguish viral conjunctivitis from bacterial preseptal cellulitis 4.

Blepharoconjunctivitis

Chronic blepharitis with secondary conjunctivitis can mimic preseptal cellulitis:

• Eyelid margin erythema and scaling rather than diffuse eyelid swelling 4
• Collarette formation at the base of eyelashes (characteristic of staphylococcal blepharitis) 4
• Chronic, recurrent course rather than acute presentation 4
• Bilateral involvement is more common 4

In children, blepharoconjunctivitis is fairly common and may lead to chronically inflamed lids, but lacks the acute purulent features of preseptal cellulitis 4.

Herpes Simplex Virus (HSV) Infection

Primary HSV infection can present with periorbital swelling:

• Vesicular lesions on the eyelid (distinctive feature) 4
• Usually unilateral presentation 4
• Watery discharge with mild follicular reaction 4
• Palpable preauricular node 4

The presence of vesicles on the eyelid skin is the key distinguishing feature from bacterial preseptal cellulitis 4.

Varicella Zoster Virus (VZV) Infection

Herpes zoster ophthalmicus can mimic preseptal cellulitis:

• Vesicular dermatomal rash or ulceration of eyelids (distinctive sign) 4
• Usually unilateral 4
• Vesicles can form at the limbus 4
• May have palpable preauricular node 4

The dermatomal distribution of vesicular lesions distinguishes VZV from bacterial cellulitis 4.

Molluscum Contagiosum with Secondary Conjunctivitis

Molluscum lesions on the eyelid can cause chronic follicular conjunctivitis with eyelid inflammation:

• Single or multiple shiny, dome-shaped umbilicated lesions on eyelid skin or margin (distinctive sign) 4
• Typically unilateral but can be bilateral 4
• Mild to severe follicular reaction 4
• Chronic rather than acute presentation 4

The presence of characteristic umbilicated lesions on the eyelid distinguishes this from acute bacterial cellulitis 4.

Idiopathic Orbital Inflammatory Syndrome (IOIS)

This non-infectious inflammatory condition can present with orbital signs mimicking infection:

• Orbital signs similar to orbital cellulitis (proptosis, ophthalmoplegia) 2
• Diagnosis of exclusion requiring imaging to rule out infection 2
• Requires corticosteroids rather than antibiotics 2

The American College of Radiology warns that assuming all periorbital swelling is infectious can lead to missing IOIS, which requires corticosteroids rather than antibiotics 2.

IgG4-Related Orbital Disease

This recently recognized inflammatory condition can mimic orbital infection:

• Accounts for a significant percentage of previously "idiopathic" orbital inflammation 2
• Presents with orbital signs similar to infection 2
• Requires immunosuppressive therapy rather than antibiotics 2

This diagnosis should be considered when patients fail to respond to appropriate antibiotic therapy 2.

Critical Clinical Algorithm for Differentiation

Step 1: Assess for orbital involvement immediately

• Check for proptosis, extraocular movement restriction, pain with eye movement, and visual acuity changes 1, 2
• If ANY orbital signs present → obtain CT orbits with IV contrast immediately 1, 3

Step 2: Identify characteristic features of non-bacterial causes

• Look for vesicular lesions (HSV, VZV) 4
• Check for umbilicated lesions (molluscum) 4
• Assess for preauricular lymphadenopathy and watery discharge (viral conjunctivitis) 4
• Evaluate for chronic eyelid margin disease (blepharitis) 4

Step 3: Consider age and predisposing factors

• Children <5 years with preseptal cellulitis typically have upper respiratory infection (68%) or trauma (20%) as predisposing factors 5, 6
• Children >5 years with orbital signs more likely have sinusitis (79-90%) 5, 6

Critical Pitfalls to Avoid

Delaying CT imaging when orbital signs are present is the most dangerous error, as it can lead to missed diagnosis of orbital cellulitis and its life-threatening complications 1, 2. The American College of Emergency Physicians emphasizes that clinical examination alone cannot reliably distinguish preseptal from postseptal cellulitis 1.

Assuming all periorbital swelling is infectious can lead to missing inflammatory conditions like IOIS or IgG4-related disease that require corticosteroids rather than antibiotics 2.

Not recognizing viral causes (HSV, VZV, viral conjunctivitis) can lead to unnecessary antibiotic use and failure to provide appropriate antiviral therapy when indicated 4.