How to differentiate between bacterial conjunctivitis and varicella-zoster virus (VZV) conjunctivitis?

Differentiating Bacterial Conjunctivitis from Varicella-Zoster Virus (VZV) Conjunctivitis

Bacterial conjunctivitis and VZV conjunctivitis have distinct clinical presentations that allow for differentiation based on specific signs and symptoms, with VZV conjunctivitis typically presenting with a unilateral vesicular dermatomal rash or ulceration of eyelids and pseudodendritic epithelial keratitis, while bacterial conjunctivitis presents with purulent discharge and papillary reaction without vesicular lesions. 1

Key Distinguishing Features

VZV Conjunctivitis

• Pathognomonic signs:
  • Vesicular dermatomal rash or ulceration of eyelids
  • Pleomorphic or non-excavated pseudodendritic epithelial keratitis of cornea
  • Usually unilateral presentation
  • History of chicken pox or exposure to individuals with active chicken pox or shingles 1
• Discharge characteristics:
  • Watery discharge rather than purulent
  • Mild follicular reaction of conjunctiva 1
• Associated findings:
  • May have palpable preauricular lymphadenopathy
  • Vesicles can form at the limbus, especially in primary infection
  • Often accompanied by significant pain 1

Bacterial Conjunctivitis

• Characteristic signs:
  • Bulbar conjunctival injection
  • Purulent or mucopurulent discharge
  • Mattering and adherence of eyelids upon waking
  • Papillary reaction in tarsal conjunctiva 1, 2
• Absence of:
  • Vesicular rash
  • Pseudodendritic keratitis
  • Dermatomal distribution 1
• Course:
  • Often starts unilaterally but may become bilateral
  • Most cases resolve within 1-2 weeks 2

Diagnostic Approach

History Elements to Focus On

1. Recent exposures:

   • Contact with individuals having viral respiratory infections (suggests viral)
   • Exposure to individuals with chicken pox or shingles (suggests VZV) 1

2. Pain characteristics:

   • Severe pain is more common with VZV
   • Mild discomfort is typical with bacterial conjunctivitis 1

3. Systemic symptoms:

   • Fever or dermatomal pain preceding ocular symptoms suggests VZV
   • Concurrent upper respiratory infection suggests viral (often adenoviral) conjunctivitis 2

Physical Examination

1. Skin examination:

   • Check for vesicular lesions in the V1 distribution of the trigeminal nerve (forehead, upper eyelid)
   • Assess for crusted lesions along the eyelid margin 1

2. Discharge assessment:

   • Purulent/mucopurulent: suggests bacterial
   • Watery: suggests viral (including VZV) 2

3. Corneal evaluation:

   • Pseudodendritic epithelial keratitis (non-excavated): VZV
   • Punctate epithelial keratitis: can occur in both but pattern differs 1

4. Conjunctival reaction:

   • Follicular reaction: more common in viral including VZV
   • Papillary reaction: more common in bacterial 1

Laboratory Testing

When clinical presentation is unclear:

1. PCR testing:

   • Highly sensitive for detecting VZV DNA from conjunctival swabs
   • Can detect VZV even in patients without obvious ocular inflammation 3

2. Viral cultures:

   • Less sensitive than PCR but can confirm diagnosis

3. Bacterial cultures:

   • Indicated for severe, recurrent, or chronic purulent conjunctivitis
   • Not routinely needed for typical bacterial conjunctivitis 1

Clinical Pearls and Pitfalls

Pearls

• VZV conjunctivitis typically occurs in the context of herpes zoster ophthalmicus and is accompanied by the characteristic dermatomal rash
• The duration of VZV DNA shedding in herpes zoster ophthalmicus is highly variable and age-dependent, with older patients (≥66 years) showing longer periods of viral shedding 3
• Bacterial conjunctivitis often causes eyelids to be stuck together upon waking due to mucopurulent discharge

Pitfalls

• VZV conjunctivitis can occur before the appearance of the characteristic skin rash, making early diagnosis challenging
• Secondary bacterial infection can complicate VZV lesions, creating a mixed clinical picture 4
• Misdiagnosis of VZV as bacterial conjunctivitis may lead to delayed antiviral treatment and increased risk of complications such as keratitis, uveitis, and corneal scarring 1, 5

Complications to Monitor

VZV Complications

• Conjunctival scarring
• Cicatricial ectropion
• Keratitis (epithelial or stromal)
• Corneal scarring
• Corneal anesthesia
• Dry eye
• Retinitis 1, 6

Bacterial Complications

• Generally self-limited with fewer long-term sequelae
• Corneal infiltrates or ulceration in severe cases
• Rarely, progression to keratitis 1

By carefully evaluating these distinguishing features, clinicians can accurately differentiate between bacterial and VZV conjunctivitis, ensuring appropriate treatment and preventing potential complications.