A 28-year-old woman from Delhi presents with progressive dyspnea, erythema nodosum, and bilateral hilar lymphadenopathy on chest X-ray. Serum calcium is elevated at 11.8 mg/dL. Histopathology shows non-caseating granulomas in lung tissue. Which feature best distinguishes sarcoidosis from chronic granulomatous disease (CGD)?

Question

Accepted Answer

B. Defective neutrophil NADPH oxidase function. ## Sarcoidosis vs. Chronic Granulomatous Disease: Pathophysiological Distinction

### Fundamental Difference

**Key Point:** Sarcoidosis is an idiopathic inflammatory disorder with intact immune function; CGD is a primary immunodeficiency caused by defective NADPH oxidase in phagocytes.

### Comparative Framework

| Feature | Sarcoidosis | Chronic Granulomatous Disease |
|---------|-------------|-------------------------------|
| **Etiology** | Idiopathic (unknown antigen) | Genetic (X-linked or autosomal recessive) |
| **Immune defect** | Intact (Th1/Th17 dysregulation) | Defective NADPH oxidase (impaired ROS production) |
| **Granuloma type** | Non-caseating | Non-caseating |
| **Calcium metabolism** | Elevated (1,25-dihydroxyvitamin D from granulomas) | Normal |
| **Catalase-positive organisms** | Not predisposed | Recurrent infections (S. aureus, Serratia, Nocardia, Aspergillus) |
| **Nitroblue tetrazolium (NBT) test** | Normal | Abnormal (cannot reduce NBT) |
| **Age of onset** | 20–40 years (adult) | Childhood (recurrent infections) |

### Why NADPH Oxidase Defect Is the Discriminator

**High-Yield:** The defective NADPH oxidase (cytochrome b~558~) in CGD prevents the respiratory burst and reactive oxygen species (ROS) production. This is the **molecular pathophysiology** that distinguishes CGD from sarcoidosis.

**Mnemonic:** **NADPH = No Active Destruction, Poor Hydrogen peroxide** — CGD patients cannot kill catalase-positive organisms.

### Clinical Correlations

**Clinical Pearl:** 
- **Sarcoidosis:** Presents in young adults with constitutional symptoms, erythema nodosum, and hypercalcemia. Granulomas form in response to an unknown antigen in genetically predisposed individuals.
- **CGD:** Presents in infancy or early childhood with recurrent, severe pyogenic infections (skin, lung, liver abscess). Granulomas form because phagocytes cannot kill organisms, leading to chronic inflammation.

### Diagnostic Tests

1. **Nitroblue Tetrazolium (NBT) Test:** Abnormal in CGD (yellow, no blue formazan); normal in sarcoidosis
2. **Dihydrorhodamine (DHR) Flow Cytometry:** Gold standard for CGD diagnosis
3. **Serum Calcium:** Elevated in sarcoidosis; normal in CGD
4. **Genetic Testing:** Identifies CYBB (X-linked) or CYBA/NCF mutations in CGD

**Warning:** Both conditions produce non-caseating granulomas, so histology alone cannot distinguish them. The key is the underlying immune mechanism: sarcoidosis has intact phagocyte function but dysregulated T-cell immunity; CGD has defective phagocyte oxidative burst.

Answer

A. Presence of non-caseating granulomas

Answer

C. Involvement of multiple organ systems

Answer

D. Elevated serum and urinary calcium levels

Explanation

Sarcoidosis vs. Chronic Granulomatous Disease: Pathophysiological Distinction

Fundamental Difference

Comparative Framework

Why NADPH Oxidase Defect Is the Discriminator

Clinical Correlations

Diagnostic Tests

Practice similar questions

Join our NEET PG community

Feature	Sarcoidosis	Chronic Granulomatous Disease
Etiology	Idiopathic (unknown antigen)	Genetic (X-linked or autosomal recessive)
Immune defect	Intact (Th1/Th17 dysregulation)	Defective NADPH oxidase (impaired ROS production)
Granuloma type	Non-caseating	Non-caseating
Calcium metabolism	Elevated (1,25-dihydroxyvitamin D from granulomas)	Normal
Catalase-positive organisms	Not predisposed	Recurrent infections (S. aureus, Serratia, Nocardia, Aspergillus)
Nitroblue tetrazolium (NBT) test	Normal	Abnormal (cannot reduce NBT)
Age of onset	20–40 years (adult)	Childhood (recurrent infections)