Annette Duck describes some of the characteristics of interstitial lung disease and how to differentiate this from asthma and COPD
Key learning points
- Many patients with interstitial lung disease (ILD) report initially being treated for chronic obstructive pulmonary disease (COPD) and asthma
- Consider ILD in those patients reporting breathlessness and cough who are unresponsive to inhaler therapy
- Spirometry is often normal in patients with early ILD
- Look out for other systemic features including clubbing, joint pains, Raynaud’s and fatigue
- Many patients with ILD present with a history of repeated chest infections in the absence of any respiratory diagnosis
- Check for inspiratory crackles on auscultation
- In suspected cases, always perform a chest X-ray
Interstitial lung disease (ILD), unlike asthma and COPD is a restrictive lung disease affecting the alveoli and interstitium.1 There have been over 200 different types of ILD reported in the medical literature so it is important to ensure a correct diagnosis if patients are to be treated appropriately.2 One of the most common types of ILD is idiopathic pulmonary fibrosis (IPF), which has a mean life expectancy of 2–4 years from diagnosis.1 Other ILDs such as sarcoidosis, hypersensitivity pneumonitis (also known as bird fancier’s or farmer’s lung) and non-specific pneumonitis are treatable if diagnosed early.
It is important to differentiate between IPF and other ILDs, and so in 2013 National Institute for Health and Care Excellence (NICE) recommended that patients suspected of having IPF should be referred to an ILD specialist centre for diagnosis and treatment recommendations.3
Until recently, there were no treatments for IPF, but now two drugs (pirfenidone4 and nintedanib5) have been licensed and have shown in clinical trials to slow down disease progression.
NICE has restricted prescribing of pirfenidone and nintedanib to specific ILD centres in England and specific prescribers in Scotland and Wales, so referral is mandatory if patients are to be given the opportunity of receiving these drugs for IPF.4,5
How to differentiate between asthma and COPD?
ILD is a restrictive lung disease causing stiffening and shrinkage of the lungs. Like COPD and asthma, ILD causes breathlessness, but only on exertion in the early stages. Breathlessness at rest is associated with advanced disease. Patients with ILD have problems getting air into their lungs rather than air out, as in COPD and asthma, which are obstructive lung diseases. In ILD the scarring makes the lungs stiff and less elastic. There are subtle differences that distinguish ILD from asthma and COPD and so it is important to take a good clinical history.
Like COPD, ILD occurs in the older age group, and although many patients may be current or ex-smokers, some have never smoked. Unlike COPD, ILD often has a more rapid onset and most patients will be able to identify a ‘beginning’ to their symptoms with comments such as: ‘It started with a cough’, ‘I found I was getting more breathless going up the stairs/hills’, ‘I’ve always been able to do everything, now I find I am getting breathless’.6 ILD patients will initially report breathlessness only on exertion. They will often state, that they are fine at rest and recover quickly.
Unlike patients with asthma, ILD patients are usually older (> 50 years), are not awoken at night with breathlessness and rarely in the early stages report coughing at night when they are resting. Cough is often reported as ‘a silly little dry cough’, ‘I cough when I do anything’, ‘when I get up, I have a hacking cough and once I bring up phlegm, I’m usually alright’.6 The cough is usually persistent and will sometimes be the first and only symptom.
Other features to check for include clubbing of the fingernails, evidence of rheumatic or inflammatory arthritis (or a history of inflammatory arthritis), fatigue or Raynaud’s, atypical skin rashes or tightness of the skin on the extremities, suggesting a connective tissue disease. It is also sensible to be aware of commonly used drugs that can induce ILD, including methotrexate, amiodarone and nitrofurantoin.
Getting the diagnosis right
Taking a thorough medical, work and leisure history initially can save a lot of time and anguish in the future. On auscultation, you may hear bilateral inspiratory (Velcro) crackles, particularly at the periphery and lung bases which might suggest IPF. A chest X-ray will usually confirm any ILD abnormality and recommend a high-resolution computed tomography (HRCT) scan and ILD specialist referral. Spirometry will often be normal in the early stages of ILD and even obstructed if the patient is a current or ex-smoker.3 Full lung function tests, including a diffusing capacity or transfer factor of the lung for carbon monoxide (DLCO or TLCO) test, will often show any early diffusion abnormality so referral to a respiratory physician is recommended in the first instance for anyone with a suspected ILD.
Early diagnosis enables better treatment in some cases of ILD and helps in planning for the future. If any doubt, seek specialist help if ILD is being considered.
This article was initiated and funded by Teva Respiratory. Teva have had no influence over content and the aforementioned trails. Topics and content have been selected and written by independent experts.