Acute, rapidly progressive idiopathic pulmonary disease that often leads to fulminant respiratory failure and acute respiratory distress syndrome (ARDS).
- AIP can be distinguished clinically from other types of interstitial pneumonia by the rapid onset of respiratory failure in a patient without preexisting lung disease.
- Often preceded by a viral URTI
History:
Louis Hamman and Arnold Rich first described it in 1935 as a fulminating diffuse interstitial fibrosis of the lungs hence AIP is also known as Hamman-Rich syndrome. In 1986, Katzenstein introduced the term AIP differentiating it from the group of chronic interstitial pneumonia. The American Thoracic Society (ATS) and European Respiratory Society (ERS) classify AIP under major idiopathic interstitial pneumonia, compared to other rare or unclassified idiopathic interstitial pneumonia.
Classification
Interstitial lung disease (ILD):
Interstitial lung disease (ILD), sometimes called diffused parenchymal diseases is a group of diseases characterized by a combination of chronic inflammation within the lung, consisting of an accumulation of chronic inflammatory cells (predominantly lymphocytes and macrophages) and increased levels of numerous pro-inflammatory cytokines, chemokines, and cell surface molecules; and varying degrees of lung fibrosis.
Idiopathic interstitial pneumonia (IIP):
Chronic, progressive fibrosing interstitial pneumonia characterized by idiopathic origin, occurrence primarily in older adults, exclusively pulmonary involvement and pattern of Usual Interstitial Pneumonia (UIP) proven by histopathology and/or radiology
American Thoracic Society/European Respiratory Society (ATS/ERS) 2002 consensus classification statement:
Histopathologic classification separating the IIPs into seven clinicopathologic entities (in order of relative frequency)
- Idiopathic pulmonary fibrosis (IPF) (47-64%)
- Nonspecific interstitial pneumonia (NSIP) (14-36%)
- Respiratory bronchiolitis ILD(10-17%)
- Cryptogenic organizing pneumonia (4-12%)
- Acute interstitial pneumonia (AIP) (< 2%)
- Lymphoid interstitial pneumonia (LIP) (< 2%)
Clinical features
Usually present as viral-like prodrome followed with shortness of breath with cough, and fever, progress rapidly to acute respiratory distress.
- Hypoxia
- Tachypnea
- Bilateral diffuse crackles
Diagnosis
Chest X-ray:
- Bilateral air-space diffuse opacities (pattern similar to ARDS)
Echocardiography (ECG):
Needed to rule out underlying cardiomyopathy or valve dysfunction
High-Resolution Computed Tomography (HRCT):
Usually abnormal in the first 12 hours
- Ground-glass opacities
- Diffuse/patchy air space consolidation
- Traction bronchiectasis (indicate progression from the exudative phase to the proliferative fibrotic phase)
Lung biopsy:
- Early phase (exudative phase): Oedema in the interstitium and alveolus
- Late phase (organizing phase): Fibroblastic proliferation and type 2 cell hyperplasia
Differential diagnosis
- Other causes of interstitial pneumonia: Cryptogenic organizing pneumonia, acute eosinophilic pneumonia, and hypersensitivity pneumonitis
- Acute exacerbation of underlying interstitial lung disease or pulmonary exacerbation of a connective tissue disease
- Acute heart failure
- Infections
- Diffuse alveolar hemorrhage
- Drug-induced lung injury
- Radiation-induced lung injury
Management
There is no proven treatment in AIP.
Supportive care:
Management is largely based on supportive care
- Mechanical ventilation (low tidal volume ventilation and other advanced ventilator modalities such as those used in ARDS)
Broad-spectrum antibiotics:
Recommended initially until infectious etiology is excluded
Empiric steroid therapy
Extracorporeal membrane oxygenation (ECMO) and lung transplantation:
After failure of conventional therapies