A 35-year-old woman from Delhi with known HIV infection (CD4 count 120 cells/μL) presents with acute onset dyspnea, fever, and dry cough for 2 weeks. She denies hemoptysis. Chest X-ray shows bilateral diffuse micronodular opacities with a 'snowstorm' appearance involving all lung fields, with relative sparing of the apices. Sputum smear is negative for acid-fast bacilli. What is the most likely diagnosis?

Question

Accepted Answer

D. Miliary tuberculosis. ## Miliary Tuberculosis: Clinical and Radiological Diagnosis

### Pathophysiology of Miliary TB
**Key Point:** Miliary TB results from hematogenous dissemination of Mycobacterium tuberculosis, typically occurring during primary infection or reactivation with erosion into a blood vessel. It is a medical emergency with high mortality if untreated.

### Why This Patient Has Miliary TB
1. **Severe immunosuppression** (CD4 <200) — permits rapid dissemination
2. **Diffuse bilateral micronodular pattern** — pathognomonic for miliary disease
3. **Negative sputum smear** — miliary TB often has lower bacillary load in sputum despite widespread lung involvement
4. **Apical sparing** — classic feature distinguishing miliary from other diffuse patterns

### Radiological Features of Miliary TB
| Feature | Characteristic |
|---------|----------------|
| **Pattern** | Diffuse, bilateral, 1–2 mm micronodules ("millet seed" appearance) |
| **Distribution** | Uniform throughout both lungs; **apices often spared** |
| **Cavitation** | Absent (unlike reactivation TB) |
| **Hilar adenopathy** | Variable; may be minimal |
| **Pleural involvement** | Uncommon unless complicated |
| **Timeline** | Acute onset (days to weeks) |

### Clinical Clues for Miliary TB
- **Immunocompromised state** (HIV, malignancy, immunosuppressive therapy)
- **Acute presentation** with constitutional symptoms
- **Negative sputum smear** despite radiological severity
- **High mortality** if diagnosis delayed (>50% if untreated)

**High-Yield:** The combination of **bilateral diffuse micronodules + apical sparing + immunocompromised host + negative sputum** = miliary TB until proven otherwise.

**Mnemonic: MILIARY TB** — **M**icronodules, **I**mmune suppression, **L**ung fields (all), **I**nfectious (hematogenous), **A**pices spared, **R**apid onset, **Y** — Yes, urgent treatment needed.

**Warning:** Do not confuse miliary TB with other diffuse micronodular patterns (sarcoidosis, silicosis, hypersensitivity pneumonitis). The clinical context (immunosuppression, fever, constitutional symptoms) and apical sparing favor TB.

**Clinical Pearl:** Miliary TB is a medical emergency. Even with negative sputum, if clinical and radiological suspicion is high, initiate anti-TB therapy immediately — waiting for culture confirmation can be fatal.

[cite:Harrison 21e Ch 205]

![Tuberculosis — Chest Imaging diagram](https://mmcphlazjonnzmdysowq.supabase.co/storage/v1/object/public/blog-images/explanation/4229.webp)

Answer

A. Endobronchial tuberculosis

Answer

B. Tuberculosis pleuritis with effusion

Answer

C. Cavitary reactivation tuberculosis

Explanation

Miliary Tuberculosis: Clinical and Radiological Diagnosis

Pathophysiology of Miliary TB

Why This Patient Has Miliary TB

Radiological Features of Miliary TB

Clinical Clues for Miliary TB

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Feature	Characteristic
Pattern	Diffuse, bilateral, 1–2 mm micronodules ("millet seed" appearance)
Distribution	Uniform throughout both lungs; apices often spared
Cavitation	Absent (unlike reactivation TB)
Hilar adenopathy	Variable; may be minimal
Pleural involvement	Uncommon unless complicated
Timeline	Acute onset (days to weeks)