What is acute interstitial pneumonia?
Acute interstitial pneumonia, or AIP, is a rare and rapidly progressive form of interstitial lung disease. It was first described as Hamman-Rich syndrome. Over days to a few weeks, the lining of the air sacs is injured, fluid and inflammatory material fill the lungs, and scarring may follow. Under the microscope the lungs show diffuse alveolar damage, the same pattern seen in acute respiratory distress syndrome (ARDS).
What distinguishes AIP is that no cause can be found: there is no infection, injury, drug, connective tissue disease or pre-existing lung fibrosis to explain it. It usually affects previously healthy adults and is a serious illness that most often requires intensive care.
Symptoms
Many patients first have a flu-like illness, followed by rapid deterioration:
- Fever, muscle aches and tiredness: often in the days before breathing becomes difficult.
- Dry cough.
- Breathlessness: progressing over days to breathlessness at rest.
- Low oxygen levels: often needing high levels of oxygen or a ventilator.
The illness usually develops over less than three weeks from the first symptoms.
Causes and risk factors
By definition, the cause of AIP is unknown. It is not linked to smoking in a consistent way and is not infectious. It affects men and women equally and can occur at any adult age.
Because AIP is a diagnosis of exclusion, the main work in the early stages is to search for treatable causes of the same lung injury pattern, including:
- Severe infections, including bacterial, viral, fungal and Pneumocystis pneumonia.
- Drug reactions and inhaled toxins.
- Connective tissue diseases and vasculitis.
- Acute eosinophilic pneumonia, which responds very well to steroids.
- A sudden worsening of previously unrecognised lung fibrosis.
- Heart failure causing fluid in the lungs.
How AIP is diagnosed
Diagnosis is made by a multidisciplinary team combining clinical, radiological and, where safe, pathological information.
| Test | What it shows |
|---|---|
| High-resolution CT of the chest | Widespread hazy and dense shadowing, and later, airway distortion and early scarring |
| Bronchoscopy with lavage | Exclusion of infection, eosinophilic pneumonia and lung bleeding |
| Blood and sputum cultures, viral tests | Infectious causes |
| Autoimmune antibody panel | Connective tissue disease or vasculitis |
| Echocardiogram and BNP | Heart failure as an alternative cause |
| Lung biopsy (selected cases) | Diffuse alveolar damage, confirming the pattern when the diagnosis remains uncertain |
Lung biopsy carries real risk in critically ill patients and is only undertaken when the result is likely to change treatment.
Treatment
Intensive care support
The cornerstone of treatment is supportive care in an intensive care unit. Most patients need mechanical ventilation using lung-protective settings, careful fluid management, prone positioning when oxygen levels are very low, and prevention of complications such as infection and clots. In carefully selected patients, extracorporeal membrane oxygenation (ECMO) may be used to support the body while the lungs recover.
Medicines
High-dose corticosteroids are commonly given, although the evidence of benefit in AIP is limited. Broad-spectrum antibiotics are usually given until infection has been excluded. Other immunosuppressive drugs have been tried, but no treatment has been proven effective in trials because the disease is so rare.
Lung transplantation
For suitable patients who do not recover, referral to a lung transplant centre may be discussed.
Outlook and recovery
AIP is a serious illness and a considerable proportion of patients do not survive, even with full intensive care. Families are kept informed openly about progress at each stage. Among those who survive, some recover near-normal lung function, while others are left with lasting scarring and reduced exercise capacity. Recurrence has been reported. Survivors are followed up with lung function tests, CT scans and pulmonary rehabilitation to rebuild strength and stamina.
When to seek urgent care
Seek emergency care immediately for breathlessness that worsens over hours or days, breathlessness at rest, low oxygen readings on a pulse oximeter, blue lips or fingertips, confusion or drowsiness. After recovery from AIP, any new fever or worsening breathing should be reported promptly.
Frequently asked questions
Is acute interstitial pneumonia the same as ARDS?
AIP looks the same as acute respiratory distress syndrome on scans and under the microscope. The difference is that ARDS has an identifiable cause, such as severe infection or injury, whereas in AIP no cause can be found.
Is it contagious?
No. AIP is not an infection and cannot be passed to family members or visitors.
Why are so many tests being done?
AIP is diagnosed only after other causes have been excluded. Many of these alternatives, such as infection or eosinophilic pneumonia, have specific treatments, so it is important to look for them thoroughly.
Can the lungs recover?
Some survivors regain near-normal lung function over months. Others have permanent scarring and need ongoing follow-up and rehabilitation.
Do steroids cure AIP?
Steroids are commonly used, but there is no strong evidence that they change the outcome in AIP. Supportive intensive care remains the main treatment.
What happens after discharge from hospital?
Survivors are reviewed in clinic with lung function tests and CT scans to measure recovery and look for scarring. Pulmonary rehabilitation helps rebuild muscle strength and stamina, and home oxygen is provided if oxygen levels remain low. Any new fever or breathlessness should be reported promptly.
Related conditions and procedures
Consult Dr. Gogineni Ratnakara Rao
Apollo Hospitals, Financial District: Monday to Saturday, 8:30 AM to 5:00 PM. Anything in Lung Clinic, Chanda Nagar: Monday to Saturday (Thursday closed), 6:00 PM to 9:00 PM.