A 28-year-old woman presents with a 3-day history of bilateral eye redness, watery discharge, and mild photophobia. She reports recent upper respiratory tract infection. On examination, she has diffuse conjunctival injection, chemosis, and preauricular lymphadenopathy. Conjunctival scrapings show predominantly mononuclear cells. Gram stain and culture are negative. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Viral Conjunctivitis ### Key Clinical Features **Key Point:** The combination of recent upper respiratory tract infection, bilateral presentation, watery discharge (not purulent), and preauricular lymphadenopathy is pathognomonic for viral conjunctivitis. **High-Yield:** Viral conjunctivitis is the most common infectious cause of acute conjunctivitis and is typically self-limited, lasting 1–2 weeks. ### Diagnostic Criteria | Feature | Viral | Bacterial | Allergic | Gonococcal | |---------|-------|----------|----------|------------| | **Onset** | Acute, often bilateral | Acute, unilateral or bilateral | Gradual, seasonal | Acute, severe | | **Discharge** | Watery, mucoid | Purulent, mucopurulent | Stringy, mucoid | Profuse purulent | | **Preauricular nodes** | Present (classic) | Absent | Absent | Absent | | **Gram stain** | Negative | Positive (cocci/rods) | Negative | Gram-negative diplococci | | **Conjunctival findings** | Follicles, chemosis | Papillae | Giant papillae | Severe edema, membrane | | **Photophobia** | Mild to moderate | Mild | Absent | Severe | ### Cytology: Mononuclear Predominance **Clinical Pearl:** The presence of predominantly mononuclear cells (lymphocytes and monocytes) on conjunctival scraping is a hallmark of viral infection. Bacterial infections show polymorphonuclear neutrophils (PMNs); allergic conjunctivitis shows eosinophils. ### Common Viral Agents **Mnemonic:** **PACE** — *Picornavirus (enterovirus), Adenovirus, Coronavirus, EBV/HSV* - **Adenovirus** (types 3, 7, 8, 19, 37): Most common; epidemic keratoconjunctivitis (EKC) with subepithelial infiltrates - **Enterovirus 70**: Acute hemorrhagic conjunctivitis with subconjunctival hemorrhages - **Herpes simplex virus (HSV)**: Unilateral, vesicular lid involvement, keratitis risk - **Varicella-zoster virus (VZV)**: Dermatomal distribution on lid; keratitis and uveitis possible ### Management 1. **Supportive care:** Cool compresses, artificial tears, lubricating ointment 2. **Avoid topical antibiotics** unless secondary bacterial infection suspected 3. **Infection control:** Hand hygiene, avoid contact lens use until resolution 4. **Topical antivirals** (e.g., acyclovir) only for HSV keratitis; not effective for adenoviral conjunctivitis 5. **Topical NSAIDs** for symptomatic relief (cautiously; avoid in HSV keratitis) **Warning:** Do NOT prescribe topical steroids empirically — risk of herpetic keratitis progression ("therapeutic disaster"). Always rule out HSV keratitis first with fluorescein staining. ### Why This Case Is Viral - **Prodrome:** Recent URTI (classic trigger for viral conjunctivitis) - **Bilateral presentation:** Suggests viral spread - **Watery discharge:** Not purulent (argues against bacterial) - **Preauricular lymphadenopathy:** Pathognomonic for viral; absent in bacterial/allergic - **Negative cultures:** Rules out bacterial; negative Gram stain excludes gonococcal - **Mononuclear cytology:** Diagnostic for viral infection