What is desquamative interstitial pneumonia?
Desquamative interstitial pneumonia, or DIP, is a rare form of interstitial lung disease. In DIP the air sacs become filled with large numbers of pigmented macrophages, the scavenger cells of the lung, together with mild inflammation and thickening of the lung tissue. The name comes from an early belief that these cells were shed (desquamated) lining cells.
The great majority of patients are current or former cigarette smokers, and DIP is grouped with the smoking-related interstitial lung diseases, alongside respiratory bronchiolitis-associated interstitial lung disease and pulmonary Langerhans cell histiocytosis. Compared with idiopathic pulmonary fibrosis, DIP has a much better outlook, particularly when smoking stops.
Symptoms
Symptoms usually develop gradually over weeks to months:
- Breathlessness: initially on exertion, such as climbing stairs.
- Dry cough: persistent and troublesome.
- Fatigue and weight loss.
- Finger clubbing: rounding of the fingertips, seen in some patients.
Fine crackles may be heard at the lung bases. Symptoms are often attributed to smoker's cough or COPD, delaying diagnosis.
Causes and risk factors
Cigarette smoking is by far the most important cause. DIP usually affects adults between their thirties and fifties and is more common in men. Less often it is linked to:
- Passive smoking and other inhaled exposures, including marijuana smoke and some occupational dusts.
- Certain medicines.
- Connective tissue diseases such as rheumatoid arthritis or scleroderma.
- Rare inherited surfactant gene abnormalities, particularly in children, who are managed jointly with paediatric pulmonology.
In a minority of patients no cause is identified.
How DIP is diagnosed
Diagnosis is made by a multidisciplinary discussion combining the history, imaging, lung function and, often, tissue samples.
| Test | What it shows |
|---|---|
| High-resolution CT of the chest | Hazy ground-glass shadowing, mainly in the lower and outer lungs, sometimes with small cysts |
| Spirometry and lung volumes | A restrictive pattern, sometimes combined with obstruction from smoking |
| Gas transfer (DLCO) | Reduced oxygen transfer, often the most sensitive abnormality |
| Six-minute walk test | Exercise capacity and oxygen levels on exertion |
| Bronchoscopy with lavage | Pigmented macrophages, and exclusion of infection and other conditions |
| Lung biopsy | Confirms the DIP pattern when CT findings are not conclusive. Cryobiopsy or surgical biopsy may be used |
Blood tests for autoimmune disease are performed to look for an underlying connective tissue disorder.
Treatment
Stopping smoking
Complete smoking cessation is the single most important treatment. Many patients stabilise or improve after stopping. Structured support, including counselling and nicotine replacement or other cessation medicines, improves the chance of success. Exposure to second-hand smoke and other inhaled irritants should also be avoided.
Corticosteroids
Oral corticosteroids are used for patients with significant symptoms or impaired lung function, or who do not improve after stopping smoking. Many respond well. Other immunosuppressive drugs are occasionally considered for steroid-dependent disease, and treatment is coordinated with rheumatology when a connective tissue disease is present.
Supportive care
Vaccinations, pulmonary rehabilitation and oxygen therapy where needed support recovery. Coexisting COPD is treated in its own right.
Outlook and follow-up
The outlook for DIP is generally good, and most patients survive long term, especially after quitting smoking. A minority have progressive disease with increasing fibrosis despite treatment, and these patients are monitored closely and assessed for antifibrotic therapy or transplant referral as appropriate. Follow-up includes lung function tests and periodic CT scans. Relapse can occur, particularly if smoking resumes. Patients who remain smoke-free and attend regular review usually maintain stable lung function and can return to normal work and daily activities.
When to seek urgent care
Seek urgent medical attention for breathlessness at rest or that worsens over a few days, low oxygen readings on a pulse oximeter, chest pain, coughing up blood, high fever, or blue lips or fingertips. Sudden chest pain with breathlessness may indicate a collapsed lung, particularly in patients with lung cysts.
Frequently asked questions
Will stopping smoking cure DIP?
Stopping smoking is the most important step, and many patients improve or stabilise after quitting. Some also need steroid treatment. Continued smoking makes progression and relapse more likely.
Is DIP the same as pulmonary fibrosis?
DIP is a type of interstitial lung disease, but it is different from idiopathic pulmonary fibrosis. It is mostly inflammatory, responds to treatment and has a much better outlook, although a minority of patients develop fibrosis.
Can non-smokers get DIP?
Yes, although it is uncommon. DIP in non-smokers may be linked to other inhaled exposures, medicines, connective tissue diseases or, in children, inherited surfactant abnormalities.
Do I need a lung biopsy?
Not always. When the CT scan, smoking history and other tests fit well, the diagnosis can sometimes be made without biopsy. A biopsy is advised when the picture is uncertain.
Is it safe to use e-cigarettes instead of smoking?
Vaping is not recommended as a safe alternative for people with lung disease. The aim is to stop all inhaled smoke and vapour, with support from approved cessation treatments.
How long does treatment take?
Improvement after stopping smoking and starting steroids usually occurs over weeks to months. Steroids are reduced gradually once lung function and the CT scan improve, and follow-up continues for several years to detect any relapse or progression.
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.