Pulmonary fibrosis is a somewhat generic term that describes scarring in the lungs. Idiopathic pulmonary fibrosis (IPF) is a very specific term that describes a specific disease process that leads to progressive scarring in the lungs. During the evaluation of scarring in the lungs, your doctor considers a variety of diseases that can cause scarring in the lungs. Two of the most common are IPF and non-specific interstitial pneumonitis (NSIP). Both diseases cause cough and shortness of breath. Both diseases lead to abnormal CT scans of the lungs. However, there are some very important differences.
Symptoms of NSIP vs. IPF
Symptoms are not able to distinguish IPF from NSIP. In some cases, cough may be more prominent in IPF but this is not reliable. There is a broad overlap in ages for the two diseases. In general, both affect patients over 50 years of age. The physical exam may reveal prominent crackles in the lungs. IPF patients are more likely to have clubbing of the fingers.
Pulmonary function testing is similar with the two diseases as well. Even high resolution CT scans of the chest can have substantial overlap. However the high resolution CT chest often provides enough information to separate the two diseases. The classic pattern on CT scanning for NSIP is a diffuse haziness or “ground glass” that is found at the bases of the lungs. There is an absence of honeycomb change (thickened scarred areas that look like a honeycomb). In many patients the high resolution CT scan of the lungs provides enough information to confirm IPF or NSIP.
In some patients there is no way to distinguish IPF from NSIP without a lung biopsy. At present, the best type of lung biopsy is a VATS (video-assisted thoracoscopic surgery). This procedure involves using two ports or small holes in your chest and taking a couple of biopsies of the lung. Bronchoscopic lung biopsy (biopsy of the lung through a small camera advanced down your throat and then directed into the lungs) is still not very reliable in making a confident diagnosis due to the small size of the biopsies obtained. Click here to learn more about surgical lung biopsy in pulmonary fibrosis.
Why is it important to distinguish IPF from NSIP?
The treatments are entirely different. For IPF we have compelling data that immunosuppression (medicines that suppress your immune system don’t work). In fact a large study showed that patients treated with prednisone and azathioprine (a strong immunosuppressant) did worse than those not treated at all. On the other, the treatment for NSIP is usually prednisone and other immunosuppressants.
Do all patients with NSIP respond to treatment with prednisone or other immunosuppressants?
No. NSIP comes in two distinct types—cellular and fibrotic. Cellular NSIP generally responds well to treatment. Fibrotic NSIP is more difficult to treat.
At the present time we have no data suggesting any benefit to using IPF treatments in NSIP. However, studies are ongoing that are looking at this very question. As of November 2017, I do not favor the “off label” use of these medications for several reasons: 1) the medications have substantial side effects, 2) the use of an unproven medication in place of a medication with a track record of efficacy is not a good plan, 3) the high cost of the medications makes getting insurance approval difficult when used in an indication other than IPF.