A 52-year-old man with a 15-year history of chronic granulomatous disease (CGD) presents with recurrent bacterial and fungal infections. Biopsy of a chronic draining sinus tract from his arm shows suppurative granulomas with central abscess formation surrounded by epithelioid histiocytes and multinucleated giant cells. Bacterial culture grows Staphylococcus aureus. What is the pathologic mechanism underlying the formation of suppurative granulomas in this patient?

Explanation

## Pathophysiology of Suppurative Granulomas in CGD ### Understanding Chronic Granulomatous Disease **Key Point:** CGD is a primary immunodeficiency characterized by defective NADPH oxidase in phagocytes, preventing the respiratory burst and oxidative killing of microorganisms. ### The NADPH Oxidase Defect 1. **Normal phagocyte function:** - Bacteria engulfed → NADPH oxidase activated - Generates superoxide anion (O₂⁻) → hydrogen peroxide (H₂O₂) - Myeloperoxidase converts H₂O₂ → hypochlorous acid (HOCl) - Microorganism killed 2. **In CGD:** - NADPH oxidase defective (X-linked or autosomal recessive) - No respiratory burst → no ROS production - Bacteria survive intracellularly despite phagocytosis - Persistent antigen stimulation → chronic granuloma formation ### Why Suppurative (Not Non-Caseating)? **High-Yield:** Suppurative granulomas form because: - Macrophages cannot kill the engulfed bacteria - Bacterial toxins and enzymes cause necrosis - Central abscess with pus (dead neutrophils + bacteria) - Surrounded by epithelioid cells attempting containment - **Clinical Pearl:** This is a **failed granuloma** — the immune system cannot sterilize the lesion ### Histologic Features | Feature | Suppurative Granuloma (CGD) | Non-Caseating (Sarcoidosis) | Caseating (TB) | |---------|-----|--------|----| | **Central necrosis** | Purulent (pus) | Absent | Caseous (acellular) | | **Bacteria present** | Yes (culturable) | No | Yes (acid-fast) | | **Epithelioid cells** | Present | Present | Present | | **Giant cells** | Present | Present | Present | | **Outcome** | Chronic drainage | Resolution/fibrosis | Cavitation | ### Diagnostic Confirmation in CGD **Key Point:** - **Nitroblue tetrazolium (NBT) test:** Negative (no respiratory burst) - **Dihydrorhodamine (DHR) flow cytometry:** Abnormal (gold standard) - **Genetic testing:** CYBB (X-linked) or CYBA/NCF1/NCF2 (autosomal recessive) ### Clinical Consequences 1. **Recurrent infections** with catalase-positive organisms (S. aureus, Burkholderia, Serratia, Nocardia, Aspergillus) 2. **Chronic suppurative lesions** (draining sinuses, osteomyelitis) 3. **Granuloma formation** as failed attempt at containment 4. **Complications:** Granulomas may obstruct GI or GU tract ### Mnemonic for CGD Organisms: **SLANG** - **S**taphylococcus aureus (most common) - **L**isteria monocytogenes - **A**spergillus (fungal) - **N**ocardia - **G**ram-negative: Burkholderia, Serratia ### Management - **Prophylaxis:** Trimethoprim-sulfamethoxazole + itraconazole - **Acute infections:** Aggressive antibiotics (prolonged courses) - **IFN-γ:** Enhances macrophage function (modest benefit) - **Gene therapy / Stem cell transplant:** Emerging curative options [cite:Robbins 10e Ch 6; Harrison 21e Ch 375]