A 32-year-old man with HIV/AIDS (CD4 count 18 cells/μL) presents with severe retinal inflammation, floaters, and progressive visual loss over 2 weeks. Fundoscopy reveals hemorrhagic retinal infiltrates with granular appearance and minimal vitritis. He denies pain. What is the most likely diagnosis and the appropriate first-line antiviral agent?

Explanation

## Diagnosis: CMV Retinitis **Key Point:** CMV retinitis is an opportunistic infection that occurs almost exclusively in severely immunocompromised patients (CD4 < 50 cells/μL). It is the most common viral cause of retinitis in AIDS patients. ## Clinical Features of CMV Retinitis | Feature | CMV Retinitis | ARN (VZV/HSV) | HSV Retinitis | |---------|---------------|---------------|---------------| | CD4 threshold | < 50 cells/μL | Variable (can occur at higher CD4) | Rare, < 20 cells/μL | | Presentation | Painless, floaters, visual loss | Acute pain, photophobia, ARN | Fulminant, hemorrhagic | | Fundoscopy | Hemorrhagic infiltrates, granular, minimal vitritis | Peripheral white granular lesions, heavy vitritis | Hemorrhagic, necrotic | | Vitritis | Minimal ("pizza pie" or "cottage cheese and ketchup") | Heavy | Moderate to heavy | | Speed | Slow, indolent | Rapid (days to weeks) | Rapid | **High-Yield:** The **hemorrhagic/granular appearance with minimal vitritis** in a patient with CD4 < 50 is pathognomonic for CMV retinitis. The lack of pain and vitritis inflammation distinguishes it from ARN. ## First-Line Antiviral Therapy for CMV Retinitis **Clinical Pearl:** Intravenous ganciclovir or foscarnet are the standard induction agents: 1. **Intravenous ganciclovir** 5 mg/kg IV twice daily × 14–21 days (induction), then maintenance 5 mg/kg daily - Preferred if neutropenia is not present - Better CNS penetration - Risk: myelosuppression (neutropenia, thrombocytopenia) 2. **Intravenous foscarnet** 60 mg/kg IV three times daily × 14–21 days (induction), then maintenance 90–120 mg/kg daily - Preferred if ganciclovir-resistant or neutropenic - Risk: nephrotoxicity, electrolyte abnormalities **Mnemonic:** **CMV retinitis = CD4 < 50 + Ganciclovir/Foscarnet IV** — C ytomegalovirus, M ust have M assive immunosuppression (CD4 < 50), G anciclovir or F oscarnet I V. ## Why Immune Reconstitution is Critical **Warning:** Antiviral monotherapy alone is insufficient. CMV retinitis will progress unless the patient's CD4 count is restored through antiretroviral therapy (ART). The goal is CD4 > 100–150 cells/μL for at least 3 months before discontinuing CMV prophylaxis. ```mermaid flowchart TD A[CD4 < 50 + visual symptoms]:::outcome --> B{Fundoscopy findings?}:::decision B -->|Hemorrhagic infiltrates + minimal vitritis| C[CMV retinitis]:::outcome B -->|Peripheral white lesions + heavy vitritis| D[ARN - VZV/HSV]:::outcome C --> E[IV ganciclovir or foscarnet]:::action D --> F[IV acyclovir high-dose]:::action E --> G[Start/optimize ART]:::action F --> H[Start/optimize ART]:::action G --> I[CD4 recovery > 100–150]:::outcome H --> I ```