Idiopathic Pulmonary Fibrosis (IPF) differential diagnoses
Vincent Cottin discusses the diseases IPF is often confused with NSIP
IPF is mostly confused with NSIP (Nonspecific interstitial pneumonia) and this is especially NSIP in the context of connective tissue disease. Because the imaging between IPF and NSIP can be close on the imaging and the patients may have very similar features especially crackles on lung auscultation and suffer from dyspnoea on exertion and sometimes finger clubbing. But one of the clues is the age in general of the patient. It has been shown that if the patient is younger than 50 then the diagnosis of IPF is very unlikely even if you are in the context of idiopathic interstitial pneumonia and on the other hand if the patient is older than 70 especially if he is male, especially if he is a smoker then the diagnosis of IPF becomes very likely. And in-between if it is female, if she has Raynaud's phenomenon, if she is less than 50 then again it is more likely to be NSIP and especially in the setting of connective tissue disease.
The other differential diagnosis that is quite common but the frequency depends on the area where you live is hypersensitivity pneumonitis (HP). And this is a condition which is related to exposure, to organic antigens and sometimes it’s very easy to diagnose because you just ask to the patient if he has birds at home or what type of job he is doing and if he is mentioning, if he is a farmer or if he is working on cheese or on fungus and so on it might be easy to suspect this diagnosis but very often the exposure is much more hidden and difficult to suspect especially for example domestic fungus exposure or if he has a Jacuzzi at home or going to the Jacuzzi somewhere. And this really needs some careful and long discussion with the patient to evaluate all the possible exposures.
And on imaging, high per cent hypersensitivity pneumonitis may look like UIP. You have some forms with honeycombing, so this is very similar to IPF. You have some forms with the UIP on the pathology, so again this is a very similar pathology at least in some of the cases.
And also in common cases HP has on imaging some traction bronchiectasis, in addition, with reticulation and this may be very close to what you see in some possible UIP features of IPF.
Add-on to question 1:
Once we know it is idiopathic interstitial pneumonia we have to separate IPF from the non IPF diagnosis. In the non IPF diagnosis we again have six different conditions but really the important step is the difference between IPF and the other ones, especially non-specific interstitial pneumonia NSIP (Nonspecific interstitial pneumonia) because there is a major difference in the long-term prognosis and also in management and treatment between IPF and NSIP.