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Definition
Numerous conditions make up the
group of disorders called interstitial lung disease. Most cause
progressive scarring of lung tissue that eventually affects your
ability to breathe and get enough oxygen into your bloodstream,
but beyond this, the disorders vary greatly.
Although most cases of interstitial
lung disease develop gradually, a few come on suddenly. Doctors
can pinpoint why some cases of interstitial lung disease occur,
but many have no known cause.
In all cases, lung scarring, once it
occurs, is generally irreversible. Medications occasionally can
slow the damage of interstitial lung disease, but many people
never regain full use of their lungs. Researchers hope that
newer drugs, many of them still experimental, may eventually
prove more effective in treating interstitial lung disease.
Symptoms
Despite the wide variety of
disorders classified as interstitial lung disease, the signs and
symptoms are often similar:
Because these problems are vague and
tend to develop gradually — often long after you have
irreversible lung damage — you may attribute them to aging, to
being overweight or out of shape, or to the residual effects of
an upper respiratory infection.
Symptoms tend to become
progressively worse, however, and eventually you may notice
you're getting out of breath during routine activities — getting
dressed, talking on the phone, even eating. At this point,
breathing problems become impossible to ignore.
Other, far less common signs and
symptoms of some types of interstitial lung disease include
wheezing, chest pain and clubbing of the fingers, a physical
sign that occurs when your fingertips painlessly enlarge and the
nails curve over the tops of your fingertips.
Causes
Each time you inhale, air travels to
your lungs through two major airways called bronchi. Inside your
lungs, the bronchi subdivide like the roots of a tree into
smaller airways (bronchioles) that finally end in clusters of
tiny air sacs (alveoli). Within the walls of the air sacs are
small blood vessels (capillaries) where oxygen is added to your
blood and carbon dioxide — a waste product of metabolism — is
removed.
In interstitial lung disease, the
walls of the air sacs may become inflamed, and the tissue (interstitium)
that lines and supports the sacs becomes increasingly thickened
and scarred. Normally, the air sacs are highly elastic,
expanding and contracting like small balloons with each breath.
But scarring (fibrosis) causes the thin, interstitial tissue to
become stiffer and thicker, making the air sacs less flexible.
Instead of being soft and elastic, scarred air sacs have the
texture of a stiff sponge, which makes it more difficult to
breathe and harder for oxygen to enter your bloodstream.
Scarring in interstitial lung
disease seems to occur when an injury to your lungs triggers an
abnormal healing response. Ordinarily, your body generates the
right amount of tissue to repair damage. But in interstitial
lung disease, the repair process goes awry, producing excess
scar tissue that increasingly interferes with lung function.
One
disorder, many causes
Because interstitial lung disease has a wide range of causes,
determining the reason for an initial injury to lung tissue can
be difficult. Some of the many possible precipitating factors
include:
-
Occupation and environmental
factors. Long-term exposure to a number of toxins or
pollutants can lead to serious lung damage. Workers who
routinely inhale silica dust (silicosis), asbestos fibers
(asbestosis) or hard metal dust are especially at risk of
debilitating lung disease. So are people exposed to certain
chemical fumes and ammonia or chlorine gases.
-
But chronic exposure to a wide range
of substances, many of them organic, also can damage your
lungs. Among these are grain dust, sugar cane, and dust from
bird and animal droppings. Other substances, such as moldy
hay, can be a problem when they cause a hypersensitivity
reaction in the lungs (hypersensitivity pneumonitis). Even
bacterial or fungal overgrowth in poorly maintained
humidifiers and hot tubs can cause lung damage.
-
Infections. These include viral
infections such as cytomegalovirus, a particular problem for
people with compromised immune systems; some bacterial
infections, including pneumonia; fungal infections such as
histoplasmosis; and parasitic infections.
-
Radiation. Some people who receive
radiation therapy for lung or breast cancer show signs of
lung damage long after their initial treatment. The severity
of the damage may depend on how much of the lung is exposed
to radiation, the total amount of radiation administered,
whether chemotherapy also is used and the presence of
underlying lung disease.
-
Drugs. Some drugs can damage the
interstitium of the lungs, especially chemotherapy drugs,
medications used to treat heart arrhythmias and other
cardiovascular problems, certain psychiatric medications,
and some antibiotics.
-
Other medical conditions.
Interstitial lung disease can occur with other disorders.
Often, those conditions don't directly attack the lungs, but
instead involve systemic processes that affect tissue
throughout the body. Among these are connective tissue
disorders and hematological diseases, including lupus,
scleroderma, rheumatoid arthritis, dermatomyositis,
polymyositis, Sjogren's syndrome and sarcoidosis.
Idiopathic
pulmonary fibrosis: When the cause isn't known
Although doctors can determine why some people develop
interstitial lung disease, in many cases the cause isn't known.
Disorders without a known cause are considered a subset of
interstitial lung disease and are grouped together under the
label idiopathic pulmonary fibrosis or idiopathicinterstitial
lung disease. Although the idiopathic diseases have certain
features in common, each also has unique characteristics.
Usual
interstitial pneumonitis is the most prevalent of the
idiopathic interstitial lung diseases. Because it's so common,
the terms "usual interstitial pneumonitis" and "idiopathic
pulmonary fibrosis" are often used interchangeably. Because
usual interstitial pneumonitis develops in patches, some areas
of the lungs are normal, others are inflamed and still others
are marked by scar tissue. The disease affects more men than
women and usually develops in people over 50.
Although the names are nearly
identical, pneumonitis is not the same as pneumonia. Pneumonitis
is lung inflammation without infection, whereas pneumonia is
lung inflammation that results from infection. In addition,
pneumonia is generally limited to one or two areas of the lungs,
but pneumonitis involves all five lobes — two in the left lung
and three in the right.
Other, less common types of
idiopathic pulmonary fibrosis include nonspecific interstitial
pneumonitis, bronchiolitis obliterans with organizing pneumonia
(BOOP), respiratory bronchiolitis-associated interstitial lung
disease, desquamative interstitial pneumonitis, lymphocytic
interstitial pneumonitis and acute interstitial pneumonitis.
Risk factors
Factors that may make you more
susceptible to interstitial lung disease include:
-
Age. Although infants and children
sometimes develop interstitial lung disease, the disorder is
much more likely to affect adults. Idiopathic forms of the
disease usually develop in adults over 50.
-
Your sex. Given the wide range of
disorders classified as interstitial lung disease, it's hard
to say definitively whether the disease affects one sex more
than the other. But there are a few notable exceptions.
Lymphangioleiomyomatosis (LAM), for example, a rare disorder
in which muscle cells invade and eventually obstruct the
airways and blood and lymph vessels in the lungs, affects
only women of childbearing age. And lung diseases resulting
from exposure to occupational toxins are much more common in
men than they are in women.
-
Exposure to occupational and
environmental toxins. If you work in mining, farming or
construction or for any reason are exposed to pollutants
known to damage your lungs, your risk of interstitial lung
disease greatly increases.
-
Radiation and chemotherapy. Having
radiation treatments to your chest or using some
chemotherapy drugs makes it more likely that you'll develop
lung disease.
-
Oxygen. Inhaling very high levels of
oxygen for more than 48 hours can harm the lungs — even
normal lungs — and can initially cause interstitial
pneumonitis. While physicians use the lowest flow of oxygen
necessary to maintain safe oxygen levels in the blood, if
very high levels of oxygen therapy must be continued for
several days to weeks, interstitial fibrosis can sometimes
occur.
Risk
factors for idiopathic interstitial lung disease
Researchers have identified certain factors that appear to
increase the risk of idiopathic lung disease, even though the
cause of the disorder isn't yet known.
-
Smoking. Some forms of interstitial
lung disease are more likely to occur in people with a
history of smoking, and active smoking may make the
condition worse. The risk seems to increase with the number
of years and the number of cigarettes smoked.
-
Genetic factors. One rare type of
idiopathic interstitial lung disease runs in families.
Called familial pulmonary fibrosis, it's similar to other
forms of the disease. Although research is being done on
familial pulmonary fibrosis, researchers haven't yet
identified the genes that may be involved.
-
Gastroesophageal reflux disease (GERD).
Researchers are investigating a possible link between
idiopathic interstitial lung disease and gastroesophageal
reflux disease, which occurs when stomach acid or,
occasionally, bile salts back up into your esophagus.
When to seek medical advice
By the time signs and symptoms such
as breathlessness and cough appear, irreversible lung damage has
often already occurred. Nevertheless, it's important to see your
doctor at the first sign of breathing problems. Many conditions
other than interstitial lung disease can affect your lungs, and
getting an early and accurate diagnosis is important for proper
treatment.
Tests and diagnosis
Identifying and determining the
cause of interstitial lung disease can be extremely challenging.
An unusually large number of disorders fall into this broad
category. What's more, the distinction between interstitial lung
disorders with identifiable causes and those with no known cause
isn't always clear, and the nomenclature and classification
systems of both have historically been confusing and
controversial.
In addition, the signs and symptoms
of a wide range of medical conditions — among them chronic
obstructive pulmonary disease (COPD), heart failure and asthma —
can mimic interstitial lung disease, and doctors must rule these
out before making a definitive diagnosis.
To help cut through the confusion
and rule out other possible illnesses, doctors normally begin by
taking a comprehensive medical history, focusing especially on
occupational exposure to lung-damaging toxins, on medications
and on the presence of health problems commonly associated with
lung disorders.
But although a medical history and
physical exam can be useful in ruling out certain conditions,
they can't accurately diagnose interstitial lung disease.
Instead, doctors normally rely on tests such as:
-
Chest X-ray. Although this is often
the first test given in cases of suspected lung problems, a
chest X-ray isn't as effective as a CT scan in diagnosing
interstitial lung disease. It can, however, help eliminate
conditions that cause signs and symptoms similar to those of
interstitial lung disease, including emphysema and a
collapsed lobe of one of the lungs.
-
High-resolution computerized
tomography (HRCT) scan. Whereas a traditional chest X-ray
produces two-dimensional images of your lungs, a
computerized tomography scan uses an X-ray-sensing unit and
a large computer to create cross-sectional images that are
far more detailed. A high-resolution CT scan goes even
further, showing lung tissue in great detail and providing
more information than conventional CT scans do.
-
Pulmonary function tests (PFTs).
These noninvasive tests check how well your lungs function.
For the test, you're usually asked to blow into a simple
instrument called a spirometer, which measures how much air
your lungs can hold and the flow of air in and out of your
lungs. As scarring becomes worse, you're able to take less
air in and blow less out. This part of the test takes just a
few minutes. Full PFTs, which give far more information and
take longer, can measure the amount of gases exchanged
across the membrane between your alveolar wall and capillary
membrane.
-
Exercise tests. Because symptoms of
interstitial lung disease are worse when you're active, your
doctor may assess your lung function while you exercise,
usually on a stationary bike or treadmill. Although specific
tests vary, your blood pressure and blood oxygen levels are
usually monitored as the difficulty of the exercise
increases.
-
Bronchoscopy (transbronchial
biopsy). In many cases, interstitial lung disease can be
definitively diagnosed only by examining a small amount of
lung tissue (biopsy). In a transbronchial biopsy, your
doctor passes a flexible, fiber-optic tube (bronchoscope)
through your mouth into your lungs and removes one or more
tissue samples, each about the size of the head of a pin.
These are then examined in a laboratory. Bronchoscopy is
performed on an outpatient basis using local anesthetic.
-
Bronchoalveolar lavage. In this
procedure, your doctor injects salt water (saline) through a
bronchoscope into a section of your lung, and then
immediately suctions it out. The withdrawn solution contains
cells from the air sacs. Although bronchoalveolar lavage
samples a larger area of the lung than other procedures do,
it may not provide enough information to diagnose a specific
interstitial lung disease. Instead, doctors often use it to
check the progress of a lung disorder or to help determine
the best treatment.
-
Video-assisted thoracoscopic
surgery. When less invasive tests don't yield a specific
diagnosis, a thoracic surgeon may perform a surgical lung
biopsy. In this procedure, a flexible tube with a camera
(endoscope) is inserted through a small incision between
your ribs, allowing the surgeon to view your lungs on a
video monitor. Surgical instruments are then inserted
through another incision, and the surgeon removes
thumbnail-sized tissue samples from two or three sites in
your lungs.
Because video-assisted thoracoscopic
surgery allows a surgeon to make small incisions in your chest
wall rather than a long cut between your ribs, you're likely to
have less pain and to heal more quickly than you are with
traditional open lung surgery. Risks of the procedure include
infection, bleeding, an air leak in the lung wall and pneumonia.
Complications
Scar tissue formation in your lungs
can lead to a series of increasingly serious complications,
including:
-
Low blood oxygen levels (hypoxemia).
Because interstitial lung disease reduces the amount of
oxygen you take in and the amount that enters your
bloodstream, you're likely to develop lower than normal
blood oxygen levels. Lack of oxygen can disrupt your body's
basic functioning, and severely low levels can be
life-threatening.
-
High blood pressure in your lungs
(pulmonary hypertension). Unlike systemic high blood
pressure, this condition affects only the arteries in your
lungs. It begins when the smallest arteries and capillaries
are compressed and obliterated by scar tissue, causing
increased resistance to blood flow in your lungs. This in
turn raises pressure within the pulmonary arteries.
Pulmonary hypertension is a serious illness that becomes
progressively worse and that eventually may prove fatal.
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Right-sided heart failure (cor
pulmonale). This serious condition occurs when your heart's
lower right chamber (right ventricle) — which is less
muscular than is the left — has to pump harder than usual to
move blood through obstructed pulmonary arteries. Initially,
your heart tries to compensate for the increased workload by
thickening its walls and dilating the chamber of the right
ventricle to increase the amount of blood it can hold. But
this measure works only temporarily, and eventually the
right ventricle fails from the extra strain.
-
Respiratory failure. Often in the
end stage of chronic lung disease, respiratory failure
occurs when blood levels of oxygen become dangerously low
or, as in the case of emphysema, carbon dioxide levels
become excessively high. Severely low blood oxygen can lead
to heart arrhythmias and unconsciousness, and high carbon
dioxide levels to sleepiness and confusion. Eventually,
respiratory failure may prove fatal.
Treatments and drugs
Interstitial lung disease caused by
toxins or drugs can sometimes be reversed when you're no longer
exposed to those substances. But in people for whom this isn't
the case, the outlook is less promising. That's because the drug
therapies that are currently available can have serious side
effects and often aren't effective. Treatments for interstitial
lung disease include:
-
Corticosteroid drugs. Although these
anti-inflammatory drugs are the initial treatment of choice,
they help a minority of people with interstitial lung
disease. Those most likely to benefit have a nonidiopathic
disorder and reversible changes in their lungs.
Corticosteroids seldom improve lung function in people with
idiopathic pulmonary fibrosis, and when they do, the
benefits are usually temporary.
-
In general, you take corticosteroids
for several months until symptoms improve and then you
slowly taper off the medication. If your symptoms return,
your doctor may recommend further corticosteroid therapy or
an immunosuppressive drug such as azathioprine. Taken for
long periods of time or in large doses, corticosteroids can
cause a number of side effects, including glaucoma, bone
loss, high blood sugar levels leading to diabetes, poor
wound healing and increased susceptibility to infection.
-
Cytotoxic drugs. Azathioprine, which
is normally used to prevent organ rejection after a
transplant, and the anti-cancer drug cyclophosphamide may be
used to treat interstitial lung disease. The drugs are
prescribed when corticosteroids fail to improve symptoms or,
increasingly, as a first-line treatment in combination with
steroids. Cytotoxic drugs can cause severe side effects,
including reduced production of red blood cells and an
increased risk of infection and certain cancers.
-
Anti-fibrotics. These drugs — such
as bosentan, colchicine, interferon gamma-1b, penicillamine
and pirfenidone — are sometimes used to help reduce the
development of scar tissue. In clinical studies, they showed
promise for slowing the progression of lung damage without
suppressing the immune system, but real-world results have
generally been disappointing.
-
Antioxidants. Oxidation is a natural
process that leads to cell and tissue damage. The process
may play a role in the development of scarring in the lungs
(pulmonary fibrosis). One trial of the antioxidant
acetylcysteine found modest improvements in lung function in
people with idiopathic pulmonary fibrosis, though no
significant changes were seen in mortality rates.
-
Oxygen therapy. Depending on the
severity of your symptoms and your activity level, your
doctor may recommend oxygen therapy. Although oxygen can't
stop lung damage, it can make breathing and exercise easier
and prevent or lessen complications from low blood oxygen
levels. Oxygen therapy may also improve your sleep and sense
of well-being. It can also reduce blood pressure in the
right side of your heart.
-
You're most likely to receive oxygen
therapy when you sleep or exercise, although some people may
use oxygen therapy around the clock. Children with
interstitial lung disease also are likely to need oxygen
therapy.
-
Pulmonary rehabilitation. This is a
formal program for people with chronic lung disease that
includes, but goes far beyond, medical management. The aim
of pulmonary rehabilitation is not only to treat a disease
or even improve daily functioning, but also to help people
with pulmonary fibrosis live full, satisfying lives. To that
end, pulmonary rehabilitation programs focus on exercise, on
teaching you how to breathe more efficiently, on education,
and on emotional support and nutritional counseling.
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Most often, this multifaceted
approach requires a team of health care providers that may
include a doctor, nurse, rehabilitation specialist,
dietitian and social worker. Programs can vary widely,
however. Your doctor can usually tell you about pulmonary
rehabilitation programs in your area. Or contact the
American Lung Association at 800-LUNGUSA, or 800-586-4872,
for more information.
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Lung transplantation. This may be an
option for people with severe interstitial lung disease who
aren't likely to benefit from other treatment options.
In order to be considered for a
transplant, you must agree to quit smoking if you smoke, be
healthy enough to undergo surgery and post-transplant
treatments, be willing and able to follow the medical program
outlined by the rehabilitation and transplant team, and have the
patience and emotional strength and support to undergo the wait
for a donor organ. The last is particularly important because
donor organs are in short supply.
In general, single-lung transplants
are more successful in people with interstitial lung disease
than double-lung transplants are.
Lifestyle and home remedies
Being involved in your own treatment
and staying as healthy as possible are essential to living with
interstitial lung disease. For that reason, it's important to:
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Stop smoking. A strong association
exists between smoking and idiopathic interstitial lung
disease, the most severe and potentially lethal of the
disorders. Talk to your doctor about options for quitting,
including smoking cessation programs, which use a variety of
proven techniques to help people quit.
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Exercise regularly. Exercise is a
double-edged sword for people with lung disease; it requires
an increased intake of oxygen, and it makes symptoms worse.
At the same time, exercise is essential for maintaining lung
function, for reducing stress, and for maintaining overall
health and well-being.
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If you're already exercising, don't
stop. And if you're not currently physically active,
consider starting with a moderate workout, such as riding a
stationary bike or walking.
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If you've been prescribed oxygen for
regular use, be sure to use it when you exercise. You might
also ask your doctor for a referral to an exercise
physiologist, who can design an exercise program
specifically for you.
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Eat well. People with lung disease
may lose weight both because it's uncomfortable to eat and
because of the extra energy it takes to breathe. Yet a
nutritionally rich diet that contains adequate calories is
essential. The type of food you eat, the time of day and the
size of portions can all play a role in getting the
nourishment you need.
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Because it's often easier to breathe
when your stomach isn't completely full, you may want to eat
smaller meals throughout the day rather than two or three
large ones. You might also try choosing lighter fare, such
as fruit and salads, rather than rich or fatty foods, which
take more energy to digest. A dietitian can give you further
guidelines for healthy eating.
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Enroll in a pulmonary rehabilitation
program. These programs vary widely, but in general they
focus on improving your ability to exercise and carry out
normal activities, managing shortness of breath with
breathing techniques, improving your appetite and
nutritional status, dealing with the difficult psychological
aspects of living with lung disease, and improving overall
quality of life.
By Mayo Clinic Staff
July 10, 2007
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