Pulmonary fibrosis is a chronic, progressive condition marked by the thickening and scarring of lung tissue, particularly the interstitium (the tissue and space around the air sacs of the lungs). This scarring hampers the lung’s ability to function, eventually leading to shortness of breath, dry cough, and hypoxemia. Recognizing the etiologies of pulmonary fibrosis is essential for diagnosis, treatment, and preventing progression.
To make memorization easier, medical educators and students often rely on mnemonics like “A TEA SHOP”, a clever acronym covering many of the common causes of interstitial lung diseases (ILDs) that result in pulmonary fibrosis.
Why Is It Important to Know the Causes of Pulmonary Fibrosis?
Understanding the underlying etiology is the cornerstone of pulmonary medicine, especially since:
- Some causes are reversible or preventable.
- Others require targeted immunosuppressive therapy.
- Accurate diagnosis affects prognosis and survival.
- Misdiagnosis could lead to treatment failure or iatrogenic harm.
Mnemonic Decoded: A TEA SHOP
Each letter in A TEA SHOP represents a key cause of pulmonary fibrosis. Let's explore each one in clinical detail.
A – ABPA (Allergic Bronchopulmonary Aspergillosis)
ABPA is a hypersensitivity reaction to the fungus Aspergillus fumigatus, primarily affecting patients with asthma or cystic fibrosis.
Key Features:
- Central bronchiectasis on CT
- Elevated IgE levels (>1000 IU/mL)
- Eosinophilia
- Positive Aspergillus skin test
Mechanism:
- Chronic allergic inflammation → fibrosis over time
Treat with corticosteroids and antifungals like itraconazole.
T – Tuberculosis (TB)
Chronic or improperly treated pulmonary tuberculosis can lead to fibrotic changes, especially in the upper lobes.
Clinical Signs:
- History of TB
- Cavitary lesions or calcifications on CXR
- Positive sputum AFB or GeneXpert
Mechanism:
- Healing by fibrosis post granulomatous inflammation
Anti-TB therapy must be optimized, and long-term follow-up for fibrosis is essential.
E – Extrinsic Allergic Alveolitis (Hypersensitivity Pneumonitis)
Also known as Hypersensitivity Pneumonitis (HP), this is an immune-mediated reaction to inhaled environmental antigens.
Examples:
- Farmer’s lung (moldy hay)
- Bird fancier’s lung (avian proteins)
- Humidifier lung
Imaging:
- Ground-glass opacities and centrilobular nodules on HRCT
Pathophysiology:
- Repeated exposure causes interstitial inflammation → fibrosis
Elimination of exposure and corticosteroids are key.
A – Ankylosing Spondylitis
This seronegative spondyloarthropathy not only affects the spine but also causes upper lobe pulmonary fibrosis in rare advanced cases.
Clinical Signs:
- Young male with chronic back pain
- HLA-B27 positive
- Bamboo spine on X-ray
Important to screen for restrictive lung disease in advanced disease.
S – Sarcoidosis
Sarcoidosis is a multisystem granulomatous disorder of unknown origin, often affecting the lungs.
Clinical Clues:
- Bilateral hilar lymphadenopathy
- Non-caseating granulomas
- Elevated serum ACE levels
- Skin lesions (erythema nodosum)
Stages of Pulmonary Involvement:
- Stage 1: Hilar adenopathy
- Stage 2: Adenopathy + parenchymal involvement
- Stage 3: Parenchymal only
- Stage 4: Fibrosis
Treat with corticosteroids in symptomatic patients or progressive fibrosis.
H – Histiocytosis (Langerhans Cell Histiocytosis)
This rare cause of pulmonary fibrosis is strongly associated with young adult smokers.
Features:
- Nodules and cysts on HRCT (upper lobe predominant)
- Spontaneous pneumothorax
- CD1a+ Langerhans cells in biopsy
Pathogenesis:
- Abnormal proliferation of dendritic cells → fibrosis
Smoking cessation is vital; steroids may help in early stages.
O – Occupational Lung Disease (Silicosis, Berylliosis)
Repeated exposure to certain occupational dusts and chemicals can lead to pulmonary fibrosis.
Common Culprits:
- Silicosis: Sandblasting, mining
- Berylliosis: Aerospace, electronics
- Asbestosis: Shipyard work, construction
Hallmarks:
- Silicotic nodules, pleural plaques
- Restrictive pattern on spirometry
- Risk of malignancy (e.g., mesothelioma in asbestosis)
Prevention via PPE and exposure control is key.
P – Pneumoconiosis (Coal Worker’s Pneumoconiosis)
Coal workers’ pneumoconiosis (CWP) is a classic example of pneumoconiosis, a group of lung diseases caused by inhaling inorganic dust.
Subtypes:
- Simple CWP: Minimal symptoms
- Complicated (Progressive Massive Fibrosis): Severe disability
Diagnosis:
- Occupational history
- CXR showing small nodules (upper lobes)
Preventive workplace measures and surveillance are essential.
Summary Table: “A TEA SHOP” Mnemonic for Pulmonary Fibrosis Causes
| Mnemonic | Cause | Key Features |
|---|---|---|
| A | ABPA | IgE ↑, asthma, bronchiectasis |
| T | Tuberculosis | Upper lobe scarring, AFB + |
| E | Extrinsic Allergic Alveolitis | Bird fancier’s lung, farmer’s lung |
| A | Ankylosing Spondylitis | HLA-B27+, upper lobe fibrosis |
| S | Sarcoidosis | Non-caseating granulomas, ACE↑ |
| H | Histiocytosis | Smokers, cystic lung disease |
| O | Occupational (Silicosis, Berylliosis) | Exposure-based, restrictive pattern |
| P | Pneumoconiosis | Coal worker’s, progressive fibrosis |
Diagnostic Approach to Pulmonary Fibrosis
To differentiate between these causes, a structured workup is essential:
| Investigation | Purpose |
|---|---|
| HRCT Chest | Pattern recognition: ground glass, honeycombing, nodules |
| PFTs | Restrictive pattern: ↓ TLC, ↓ DLCO |
| BAL/Biopsy | Identify specific inflammatory or fibrotic patterns |
| Serologic tests | ANA, RF, anti-CCP, ACE, IgE |
| Occupational history | Critical in suspected pneumoconiosis or EAA |
| Exposure history | Pets, birds, molds, farms |
Clinical Presentation of Pulmonary Fibrosis
| Symptom | Explanation |
|---|---|
| Dyspnea on exertion | Most common early symptom |
| Dry cough | Irritative, non-productive |
| Fatigue | Due to hypoxia |
| Clubbing | Seen in chronic cases |
| Bibasilar crackles | “Velcro-like” on auscultation |
Types of Interstitial Lung Diseases That Cause Fibrosis
Pulmonary fibrosis is part of a broader group known as Interstitial Lung Diseases (ILDs), classified as:
- Idiopathic Interstitial Pneumonias (e.g., IPF)
- Granulomatous ILDs (e.g., Sarcoidosis)
- Drug-induced (e.g., amiodarone, methotrexate)
- Connective tissue disease-related
- Hypersensitivity Pneumonitis (EAA)
Treatment Principles of Pulmonary Fibrosis
| Treatment Option | Indication |
|---|---|
| Corticosteroids | Sarcoidosis, ABPA, HP |
| Antifungals | ABPA (itraconazole) |
| Immunosuppressants | Autoimmune ILDs (methotrexate, azathioprine) |
| Antifibrotic agents | IPF (nintedanib, pirfenidone) |
| Oxygen therapy | In advanced cases |
| Lung transplantation | End-stage disease |
Frequently Asked Questions (FAQ)
What is the most common cause of pulmonary fibrosis?
Idiopathic Pulmonary Fibrosis (IPF) is the most common, but among secondary causes, occupational exposure and hypersensitivity pneumonitis are prominent.
Can pulmonary fibrosis be reversed?
Most fibrotic changes are irreversible, but progression can be slowed with early diagnosis, exposure cessation, and medication.
Is pulmonary fibrosis the same as COPD?
No. Pulmonary fibrosis is a restrictive lung disease, whereas COPD is obstructive. Their pathophysiology, treatment, and prognosis differ.
How is ABPA different from asthma?
ABPA occurs in asthmatics but is marked by fungal sensitization, central bronchiectasis, and high IgE levels, requiring antifungal therapy along with steroids.
Can sarcoidosis mimic pulmonary fibrosis?
Yes. Advanced sarcoidosis (stage IV) may present with fibrotic lung disease, often requiring differentiation from other ILDs via biopsy or imaging.
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