Interstitial lung disease is a group of diseases that affect the tissue and spaces (interstitial) around the air sacs (alveoli) in the lung. This is the place where oxygen that we breathe in is passed into the blood stream and carbon dioxide passes from the blood to the lungs to be breathed out. When these spaces are obstructed by inflammation, this exchange is impaired. When inflammation is untreated for too long, it can result in pulmonary fibrosis, in which the lungs are scarred causing serious breathing problems.
Except in inclusion body myositis, interstitial lung disease is the most common and serious complication of the inflammatory muscle diseases. Researchers estimate that 30-40% of myositis patients have some form of lung disease.
There is also a strong association between interstitial lung disease and antisynthetase antibodies. Of those patients who have interstitial lung disease, about 75% have anti-Jo-1 antibodies. Autoantibodies to MDA5 and PM-Scl (an antibody prevalent in polymyositis/systemic scleroderma overlap) are also associated with interstitial lung disease.
Symptoms can be variable, including shortness of breath, cough (usually a dry cough with no sputum), or no symptoms at all. Symptoms usually progress slowly, but respiratory distress can also occur quickly. Of those who have interstitial lung disease, the disease seems to be worse in African American patients versus Caucasian patients.
Interstitial lung disease can appear before muscle symptoms become apparent. In addition, the severity of muscle or skin disease is not necessarily an indication of the severity of lung disease. Muscle and skin symptoms may be mild or even nonexistent, but interstitial lung disease may be severe.
Diagnosis starts with a suspicion of lung involvement. The physician will listen to the breathing with a stethoscope, consider blood test results, and examine skin and muscle strength. Diagnosis typically requires additional tests, including the following:
Chest x-ray is the first step that can indicate abnormalities as well as how the disease is progressing.
Chest computerized tomography (CT) scan, especially a high-resolution CT (HRCT), is preferred as a way to detect interstitial lung disease, identify the severity of the disease, and distinguish between fibrotic disease and active inflammation in the lungs. Classic signs of ILD include ground glass opacities (a characteristic appearance that indicates inflammation in the air sacks), reduced lung volume, and bronchiectasis (enlargement of the airways).
Pulmonary function tests (PFTs) are a set of non-invasive tests in which the patient is asked to blow forcefully into a machine. PFTs measure how well the lungs take in and push air out and how efficiently they get oxygen into the blood.
Bronchoalveolar lavage is a procedure in which a tube is passed down the throat into the lungs and a sample of fluid withdrawn and tested. This may be done to rule out other causes of lung disease, such as infection.
Lung biopsy, in which a sample of lung tissue is removed for testing, may be done, if necessary.
Autoantibody blood tests can not only confirm a diagnosis of myositis, but the presence of an antisynthetase antibody can identify patients who are at risk for developing interstitial lung disease.
Treatment of interstitial lung disease is best when the plan of care is coordinated between the rheumatologist (who attends to the myositis side of the disease) and the pulmonologist (who attends to the lung disease). Ongoing care typically includes the following:
Antibiotics, including Bactrim DS, Dapsone, or Pentamadine, may be prescribed on a long-term basis to prevent infections in the lung.
Frequent pulmonary function tests (PFTs) to monitor disease progression or progress.
High resolution CT (HRCT) scans may be done to monitor disease progression or progress.
Echocardiograms or an ultrasound of the heart may be done to be sure there is no pulmonary hypertension.
Many patients need supplemental oxygen.
Other causes of breathing problems in myositis
While interstitial lung disease is by far the most common lung-related complication of myositis, other factors may also involve the chest and lungs that might make it difficult to breathe. These include the following:
Myositis can cause inflammation and weakness in the breathing muscles as well as the skeletal muscles, which makes breathing difficult or less effective.
Dysphagia (difficulty swallowing) can make the patient choke on food or fluids causing them to be aspirated (inhaled) into the lungs. This causes a chemical inflammation that can result in pneumonia.
Cardiovascular problems, especially congestive heart failure, can cause shortness of breath and other symptoms.
Pulmonary artery hypertension is a rare complication that involves increased pressure in the circulation between the heart and lung and causes the right side of the heart to become enlarged. This also can cause shortness of breath and other symptoms.
Additional information about cancer-associated myositis can be found in the Myositis Library section of this website.
Myositis and lung disease – video presentation by Dr. Dana Ascherman at the 2015 TMA Annual Patient Conference