What is Desquamative Interstitial Pneumonia?
Cigarette smoking is linked to chronic obstructive pulmonary disease (COPD), bronchogenic carcinoma (a type of lung cancer), and other specific types of lung disease that affect the tissue and spaces around the lung’s air sacs (or interstitium).
There are specific lung conditions known as Smoking-Related Interstitial Lung Disease (SR- ILD) which relates to cigarette smoking. These include Pulmonary Langerhans cell histiocytosis (PLCH), Respiratory-bronchiolitis-associated interstitial lung disease (RB-ILD), and Desquamative interstitial pneumonia (DIP).
The 2013 statement from the American Thoracic Society and the European Respiratory Society classified RB-ILD and DIP as conditions causing inflammation and scarring in the lung due to smoking (also known as smoking-related idiopathic interstitial pneumonia or SR-IIP). However, RB-ILD and DIP are different and not stages of the same condition. They have unique symptoms, imaging features, tissue changes, responses to treatment, and outlooks.
When looking at the tissue under a microscope, DIP is marked by the buildup of scavenger cells (known as macrophages) in the tiny air sacs of the lungs, followed by inflammation and scarring of the surrounding spaces.
What Causes Desquamative Interstitial Pneumonia?
While it’s mostly linked to smoking, with about 90% of cases found in smokers, DIP (Desquamative Interstitial Pneumonia) has also been related to other exposures and health conditions. This includes:
* smoking marijuana
* exposure to metals like copper, beryllium – common amongst some professionals like tool grinders, aluminum welders, machinists, workers in tire manufacturing, etc.
* exposure to fire extinguisher powder and diesel fumes at work
* working with nylon filaments in the textile industry
* taking certain medications such as sirolimus, nitrofurantoin, tocainide, and sulfasalazine
* having autoimmune diseases like scleroderma and rheumatoid arthritis
Furthermore, repeated bouts of DIP can occur after a lung transplant.
There are also certain infectious diseases, like Aspergillus, Hepatitis C, and Cytomegalovirus as well as metabolic diseases like Gaucher disease, which can be associated with DIP.
Interestingly, adult-onset DIP hasn’t been connected with any known genetic defects. Yet, when children get DIP, it’s linked to a specific genetic change in surfactant proteins B and C that cause these proteins to function badly. DIP is generally more serious in children due to this reason.
Risk Factors and Frequency for Desquamative Interstitial Pneumonia
In 1965, the condition we now know as desquamative interstitial pneumonia was first described by Liebow and colleagues. At that time, they misinterpreted certain cells in the lung’s air spaces for ones that had peeled off from the lung’s lining. Thus, they named it ‘desquamative interstitial pneumonia’. Later, it was found out that the cells are actually macrophages present within the air spaces.
The same researchers initially didn’t mention the disease’s connection with smoking. It wasn’t until 1978 that Carrington and his team highlighted this link. The disease mostly affects people aged between 40 to 60 years, with twice as many men than women being diagnosed. Most of the affected people, 60% to 87%, are smokers. Despite this, other research from Craig and Tubbs and their respective teams indicates that 40% of people in their study groups with the disease were nonsmokers.
Signs and Symptoms of Desquamative Interstitial Pneumonia
Smoking-related interstitial pneumonia often shares similar clinical signs and histopathological features. To properly diagnose a specific form of this disease, called SR-ILD, a combination of clinical, radiological, and pathological evaluations is often necessary over time. This aids in guiding appropriate treatment.
Typically, individuals exposed to cigarette smoke, recreational drugs via inhalation, or certain occupational hazards present with symptoms like a dry cough and breathlessness during exercise. It’s most commonly seen in individuals between 40 and 60 years of age, with males being more frequently diagnosed. This is likely due to their increased exposure.
Interestingly, fewer than 10% of patients show no symptoms at the time of diagnosis. However, when symptoms do occur, they are generally nonspecific. They most commonly include:
- Shortness of breath during physical activity (90% of patients)
- Persistent cough with or without sputum production (about 70% and 40% respectively)
- Very rare cases of coughing up blood
In about half the patients, physical examination reveals clubbed fingers (a change in the shape of your fingers and nails), and a certain type of crackling sound heard in the lungs during inhalation.
Testing for Desquamative Interstitial Pneumonia
Tests of your bloodstream may show an increase in specific white blood cells, called neutrophils and eosinophils. Lung function tests for this condition typically reveal a restriction in airflow and a decreased ability to transfer oxygen and carbon dioxide, which differs from the blockages commonly seen in a condition called respiratory bronchiolitis.
A chest x-ray might show a pattern of small lumps and netlike regions, primarily in the lower part of the lungs. However, this is not always the case, and the images may appear quite normal or nonspecific. In fact, normal-looking x-rays have been reported in about 3% to 22% of confirmed cases.
The preferred imaging technique is a high-resolution chest CT scan. This typically shows a consistent pattern of hazy looking areas, primarily in the lower parts of both lungs. These hazy areas are not accompanied by a honeycomb appearance, which sets it apart from some other lung conditions. As the disease progresses, different features like cysts might appear, but fibrosis, or scarring, isn’t as common as in other lung diseases.
However, in advanced stages, it has been reported that this disease can appear similar to another lung disease called NSIP. An interesting fact is that unlike many other lung diseases caused by inhaling harmful substances, the hazy areas are more common in the lower parts of the lungs in this condition.
Surprisingly, a study revealed that only 59% of diagnoses based on this type of scan were confirmed when a tissue sample was examined, underscoring the importance of a consensus amongst clinicians, radiologists, and pathologists.
While a surgical lung biopsy is still considered the most reliable way to diagnose this condition, doctors have found that a biopsy acquired through a bronchoscope may not always provide a representative tissue sample. As a result, they have started to explore less invasive procedures, such as transbronchial cryobiopsy, which provides a larger sample.
Lastly, it’s important to note that studies have found considerable similarities between this condition and another called RB-ILD, as features of both can present in different sections of the biopsy. However, the overall appearance on scans and the lung function test results are noticeably different between these two conditions.
Treatment Options for Desquamative Interstitial Pneumonia
Quitting smoking is the most crucial step a patient can take after being diagnosed. Also, if the illness is connected to certain occupational exposures, avoiding those triggers can help prevent the condition from worsening.
The most effective treatment currently known involves the use of corticosteroids, a type of medication, over several months. Alongside these, doctors often use drugs that suppress the immune system, such as azathioprine, to treat the illness. Many patients can maintain their current health status or improve with this treatment, some even achieving full recovery.
However, studies show that about a quarter of patients might continue to get worse, even with corticosteroid treatment, developing a severe lung condition called pulmonary fibrosis. For these cases, some reports suggest that a medication known as clarithromycin may be successful.
There are also isolated cases where other treatments, such as azathioprine and cyclophosphamide, have been used to treat severe breathing problems caused by this condition. For severe cases, where the lung disease has caused low oxygen levels or high blood pressure in the lungs, a lung transplant may be considered. However, there have been reports of the condition returning in people after having a lung transplant.
What else can Desquamative Interstitial Pneumonia be?
Other diseases that are connected to smoking and affect the lungs’ intricate network of tissues (also known as interstitial pneumonia) exist. These include illnesses like respiratory bronchiolitis-interstitial lung disease.
There are also multiple other kinds of lung conditions, called idiopathic interstitial pneumonias, where the cause isn’t known. Some examples include:
- Idiopathic pulmonary fibrosis: a lung disease that results in lung scarring
- Idiopathic nonspecific interstitial pneumonia: a lung disorder causing inflammation and scarring in the lung tissue
- Cryptogenic organizing pneumonia: a rare type of pneumonia causing inflammation and scarring in the lung’s small airways and air sacs
- Acute interstitial pneumonia, previously known as Hamman-Rich syndrome: a severe lung disease causing rapid inflammation and lung failure
- Idiopathic lymphoid interstitial pneumonia: a rare lung condition causing inflammation in the lung tissues
- Idiopathic pleuroparenchymal fibroelastosis: a rare, progressive lung disease causing fibrosis in the upper lung lobes
- Amiodarone toxicity: lung damage caused by amiodarone, a medication used for irregular heartbeats
What to expect with Desquamative Interstitial Pneumonia
The overall survival rate for patients ten years after diagnosis ranges from 70% to 88%.
The death rate of DIP, a disease, can vary from 6% to 28%. Research has shown that despite some cases of spontaneous improvement, two-thirds of patients with DIP see their disease progress if not treated. In one particular study, it was found that 25% of patients still had their disease get worse despite undergoing therapy with a type of medication called corticosteroids.
There are not many studies that have followed DIP patients over time to see how the disease progresses. Of the few studies conducted, one showed that the symptoms in current smokers, such as ground glass changes, emphysema, and centrilobular nodules, increased in 28% to 42%, 26% to 40%, and 33% to 35% of the individuals, respectively, over a period of 5.5 years on average.
In a smaller study involving 14 patients who were monitored for changes in the appearance of their DIP through radiological methods, an increase in cysts and a new appearance of “honeycombing” was observed in 35% of the individuals. These individuals were receiving systemic corticosteroid therapy. The ten-year survival rates for DIP are around 70%.
Also, one’s chances of survival decrease if they continue to smoke. Similarly, children with DIP, especially those with ABCA3 mutations, tend to have a more difficult prognosis.
Possible Complications When Diagnosed with Desquamative Interstitial Pneumonia
Acute interstitial pneumonitis (an inflammatory lung disease) and diffuse alveolar hemorrhage (bleeding into the lungs) are serious complications that can occur in the early stages of the disease. Some cases of these complications have been noted following diagnostic surgeries that use video-assisted thoracoscopic technology.
Some experts have noticed that DIP (desquamative interstitial pneumonia) can turn into a fibrotic form of NSIP (non-specific interstitial pneumonia), especially in its advanced stages. This is based mostly on similar features observed in tissue samples. However, the prognosis (or likely course) of this group of diseases appears to be better than NSIP or UIP (usual interstitial pneumonia).