Interstitial lung disease

Interstitial lung diseases.

Recognition: in areas of high tuberculosis prevalence, nearly every patient with dyspnoea or a cough and an abnormal CXR gets diagnosed as having either active TB, or if the sputum is negative, ‘old’ TB. This very convenient dichotomy retains credibility because it is so often correct, but it creates an unfortunate situation for those patients with potentially remediable alternative causes for their symptoms. Most patients with some form of diffuse parenchymal disease warrant further investigation if they are AFB negative and have no background history of TB, unless disease is so far advanced that specific therapy is unlikely to change outcome.

Many clinicians find the list of potential causes very long (nearly 200 entities) and there is a natural tendency to shy away from taking things further. The advent of high resolution CT scan has transformed this field – a combination of a decent history, examination, a few blood tests and a CT take you a long way to making a reasoned diagnosis. If you are stuck, having this information to present to a respiratory physician as a preliminary to bronchoscopy is valuable.

Specific pointers:

• Sputum production is relatively rare in most of these diseases, although a dry cough is common.
• Ask about extra-pulmonary symptoms such as arthritis, dysphagia and skin rashes or lumps.
• Take a history about occupation and hobbies.
• When examining the patient check for clubbing, arthritis, and skin rashes or adenopathy. The fine inspiratory crackles of fibrosing alveolitis are characteristic, especially in the presence of clubbing.

Blood tests may be helpful but can be quite expensive so proceed in series – there is usually no hurry. It is silly to get back a whole bunch of normal but gloriously expensive results when you have already reached a diagnosis from some relatively straightforward test (e.g. finding profound eosinophilia on the FBC). Often a high resolution CT scan will be the initial investigation of choice, and is sometimes diagnostic. Consider:

• FBC with differential, including eosinophil count (pulmonary eosinophilic syndromes).
• HIV – makes infections a likely cause.
• Serum IgE (drug reactions and worm infestations).
• ANCA (Wegener’s and other vasculitides).
• ANF and C3/C4 (collagen vascular diseases).
• A SACE is often requested but can be confusing as it is not that specific for sarcoidosis.

Some relatively common conditions (simply to differentiate them from the real rarities!)

• Pneumoconioses (asbestosis, silicosis, coal)
• Infections – CMV, Toxo, Pneumocystis, Ascaris.
• Malignancy – lymphoma, alveolar cell carcinoma
• Allergic reaction to drugs (methotrexate, sulphasalazine, NSAIDS, hydralazine, anticonvulsants, etc)
• Extrinsic allergic alveolitis
• Associated with collagen vascular diseases such as SLE, RA, systemic sclerosis and polymyositis
• Sarcoidosis
• Wegener’s granulomatosis
• Fibrosing alveolitis
• Interstitial pneumonias – usually requires CT or bronchoscopy or both for diagnosis
• Suppurative lung disease.

Interstitial pneumonias

There is a conflation of terminologies and diagnostic routes with pathological classifications not always being followed by distinct clinical courses. Broadly, there are those with chronic fibrosis – usual interstitial pneumonia (UIP) and non-specific interstitial pneumonia (NSIP), those that may be smoking related ( DIP or desquamative interstitial pneumonia, and respiratory bronchiolitis-interstitial lung disease or RB-ILD) and those with more acute presentations (acute interstitial pneumonia or AIP, and cryptogenic organizing pneumonia, or COP)¹

NSIP and UIP differ in that NSIP is a more uniform disease with micronodules, whereas UIP is more patchy with more honeycombing, peripheral predominance, and traction bronchiectasis.²,³

Therapy is directed at identifying causes (collagen-vascular diseases, medications) and targeting what can be addressed there; in discussion with a pulmonogist, use of corticosteroids and some other immunosuppressive agents may be indicated for the lung disease on its own.

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1. Travis WD, et al. An official American Thoracic Society/European Respiratory Society statement: Update of the international multidisciplinary classification of the idiopathic interstitial pneumonias. American Journal of Respiratory and Critical Care Medicine. 2013; 188:733 ↩

2. Raghu G, Collard HR, Egan JJ, et al. An official ATS/ERS/JRS/ALAT statement: idiopathic pulmonary fibrosis: evidence-based guidelines for diagnosis and management. Am J Respir Crit Care Med. 2011;183:788-824 ↩

3. Ebner L, Christodoulidis S, Stathopoulou T, Geiser T, Stalder O, Limacher A, et al. (2020) Meta-analysis of the radiological and clinical features of Usual Interstitial Pneumonia (UIP) and Nonspecific Interstitial Pneumonia (NSIP). PLoS ONE 15(1): e0226084. https://doi.org/10.1371/journal.pone.0226084 ↩

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