A 32-year-old man with newly diagnosed HIV (CD4 count 35 cells/μL) presents with floaters, photopsia, and progressive visual field loss over 2 weeks. Dilated fundoscopy reveals granular infiltrates with hemorrhages at the border of normal and abnormal retina in a 'cottage cheese and ketchup' pattern, primarily in the peripheral retina. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: CMV Retinitis in Advanced AIDS ### Key Clinical Features **Key Point:** The combination of severely immunocompromised state (CD4 <50), progressive visual symptoms, and the pathognomonic 'cottage cheese and ketchup' appearance (granular infiltrates with hemorrhages at the border of normal and abnormal retina) is diagnostic of CMV retinitis. ### Epidemiology & Risk Factors **High-Yield:** CMV retinitis is the most common opportunistic retinal infection in patients with CD4 <50 cells/μL. Incidence has declined dramatically with antiretroviral therapy (ART) but remains a major cause of blindness in untreated AIDS. ### Comparison of Herpesviruses in Retinitis | Feature | CMV Retinitis | HSV Acute Retinal Necrosis | VZV Progressive Outer Retinal Necrosis | Toxo Retinitis | |---------|---------------|---------------------------|----------------------------------------|----------------| | **CD4 threshold** | <50 (critical) | Variable, can occur >200 | <50 (usually) | <100 | | **Fundoscopic pattern** | Cottage cheese & ketchup | Hemorrhagic, full-thickness | Granular, outer retinal | Focal, white infiltrates | | **Hemorrhages** | Prominent at border | Extensive throughout | Minimal | Minimal | | **Speed of progression** | Slow (weeks to months) | Rapid (days to weeks) | Rapid (days to weeks) | Variable | | **Anterior uveitis** | Absent or minimal | Severe | Severe | Absent | | **Immune recovery uveitis** | Common (with ART) | Rare | Rare | Rare | | **Treatment** | IV ganciclovir, valganciclovir | IV acyclovir | IV acyclovir | TMP-SMX, pyrimethamine | ### Pathognomonic Findings of CMV Retinitis **Clinical Pearl:** The 'cottage cheese and ketchup' appearance refers to: 1. **Granular infiltrates** (cottage cheese) — areas of retinal necrosis 2. **Hemorrhages** (ketchup) — at the active border between normal and necrotic retina 3. **Peripheral location** — typically starts in the periphery and advances centripetally 4. **Indolent course** — progresses over weeks to months, unlike HSV/VZV which advance rapidly ### Distinguishing from Other Herpesviruses ```mermaid flowchart TD A[Retinitis in CD4 <50]:::outcome --> B{Speed of progression?}:::decision B -->|Slow weeks-months| C{Hemorrhages at border?}:::decision B -->|Rapid days-weeks| D[HSV or VZV]:::outcome C -->|Yes| E[CMV Retinitis]:::action C -->|No| F[Consider other causes]:::outcome D --> G{Anterior uveitis?}:::decision G -->|Severe| H[HSV ARN]:::outcome G -->|Severe| I[VZV PORN]:::outcome ``` ### Why CMV is the Answer 1. **CD4 <35** — critical threshold for CMV disease; HSV/VZV can occur at higher counts 2. **'Cottage cheese and ketchup'** — pathognomonic for CMV; HSV/VZV show hemorrhagic full-thickness necrosis 3. **Progressive over 2 weeks** — consistent with indolent CMV; HSV/VZV advance rapidly over days 4. **Peripheral location** — typical for CMV; HSV/VZV often involve the posterior pole 5. **No mention of anterior uveitis** — CMV causes minimal anterior inflammation; HSV/VZV cause severe anterior chamber reaction ### Management **High-Yield:** - **Induction:** IV ganciclovir 5 mg/kg IV BID or IV foscarnet 90 mg/kg BID for 2–3 weeks - **Maintenance:** Valganciclovir 900 mg PO BID (oral option after induction) - **Immune recovery:** Start ART immediately; immune recovery uveitis (IRU) is common as CD4 recovers - **Monitoring:** Ophthalmology follow-up every 1–2 weeks during induction; risk of retinal detachment [cite:Harrison 21e Ch 187; Robbins 10e Ch 8]