Idiopathic pulmonary fibrosis is typically seen in older male smokers, with progressive basal and peripheral predominant reticular abnormalities, traction bronchiectasis and honeycombing consistent with usual interstitial pneumonia UIP.
Description
Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive fibrosing interstitial pneumonia of unknown cause, occurring primarily in older adults. It is a type of idiopathic interstitial pneumonia and the most common of the idiopathic interstitial pneumonias. IPF is characterised histologically by a usual interstitial pneumonia (UIP) pattern.
Pathogenesis
The pathogenesis of IPF is believed to involve repetitive micro-injuries to the alveolar epithelium, leading to aberrant wound healing and fibrosis. These processes are likely driven by a complex interplay of genetic predisposition, environmental factors (e.g., smoking), and ageing.
Subtypes
There are no recognised subtypes of IPF. However, the disease can manifest with different degrees of severity and progress at variable rates.
Epidemiology, Risk Factors & Associations
- IPF typically affects older adults (over 60 years) (85%).
- Males are affected more often than females.
- The disease is strongly associated with a history of smoking.
- There may be an association with certain genetic mutations, such as mutations in the MUC5B gene.
Clinical Features
Patients with IPF typically present with progressive dyspnoea and a non-productive cough. Other features can include:
- Bilateral inspiratory crackles (“Velcro” rales).
- Finger clubbing.
Complications
- Progressive respiratory failure and death.
- Acute exacerbations.
- Increased risk of lung cancer (3-20% of patients with IPF).
- Pulmonary hypertension.
Pathological Features
Histopathology
- Macroscopic: Lungs are typically firm and cobblestone in appearance due to subpleural fibrosis.
- Microscopic: UIP pattern, characterised by temporal and spatial heterogeneity of fibrosis, fibroblast foci, honeycombing, and normal lung interspersed with fibrotic areas.
Serology
- No specific serologic markers for IPF.
Biochemistry
- No specific biochemical markers for IPF.
Radiological Features
General Features
- Characteristically demonstrates reticular abnormalities, traction bronchiectasis and honeycombing with a predominantly basal and peripheral distribution.
- Honeycombing and reticulation may be more pronounced in the subpleural regions.
- Ground-glass opacities can be present but are less extensive than reticulation.
XR
- Coarse reticular interstitial markings predominantly in the lower lung fields.
- Volume loss and honeycombing in advanced disease.
CT
- Non-contrast: Reticular opacities, honeycombing, and traction bronchiectasis, predominantly in a subpleural and basal distribution.
Grading and Staging
There is no universally accepted staging system for IPF. The disease course can be highly variable, with some patients remaining stable for many years and others rapidly progressing to respiratory failure.
Diagnosis
Diagnosis of IPF requires a combination of clinical, radiologic, and if necessary, histopathologic findings. The characteristic radiologic pattern of UIP on HRCT can be diagnostic in the right clinical context, negating the need for a lung biopsy.
Differential Diagnosis
- Non-specific interstitial pneumonia (NSIP): Characterised by ground-glass opacities and a more symmetrical distribution than IPF. Subpleural sparing is a distinguishing feature. It typically lacks the honeycombing seen in IPF.
- Chronic hypersensitivity pneumonitis (HP): Predominantly a mid-upper lung disease with centrilobular nodules, ground-glass opacities, and mosaic attenuation. Honeycombing is less common and less extensive than in IPF. History of environmental exposure to certain allergens helps in diagnosis.
- Connective tissue disease-associated interstitial lung disease (CTD-ILD): Predominantly ground-glass opacities with a peribronchovascular distribution. Reticular pattern and honeycombing can be present but are less extensive than in IPF. Clinical features of connective tissue disease guide diagnosis.
- Sarcoidosis: Characterised by bilateral hilar lymphadenopathy, with upper and mid lung predominance. Reticular pattern or honeycombing is less common and less extensive than in IPF.
- Asbestosis: Asbestosis also presents with a lower lobe and subpleural predominant fibrotic process. Distinguishing features include pleural plaques, rounded atelectasis, and diffuse pleural thickening.
- Drug-induced interstitial lung disease (DILD): Depending on the causative agent, the pattern can vary from ground-glass opacities, nodules, to fibrosis. The history of drug exposure and symptom onset aids diagnosis.
Management
- Referral to a pulmonologist for further management and consideration for lung transplant in suitable candidates.
- Antifibrotic agents such as pirfenidone and nintedanib can be used to slow disease progression.