Interstitial lung disease (ILD) comprises of a group of several diseases of different causes but similar features. It is classified as either Primary (or idiopathic) and Secondary (Secondary to some other disease). Secondary ILD commonly occurs in patients with pre-existing diseases such as rheumatoid arthritis, systemic sclerosis, sarcoidosis and occupational disorders. Hypersensitivity pneumonitis is a group of common ILDs which occur on exposure to organic dusts which happens during farming, keeping birds, manufacturing cheese, air-conditioning etc. ILD can also develop following viral infections, administration of certain drugs, high-dose radiation and radiotherapy.
Primary or idiopathic ILD is the more serious type whose cause is not identifiable. Of various kinds of idiopathic ILDs, idiopathic pulmonary fibrosis (IPF) is most important. There are a few other types of idiopathic ILDs importantly, non-specific interstitial pneumonia (NSIP), organizing pneumonias (OP), desquamative interstitial pneumonia and acute interstitial pneumonia.
Other tests may be required for identification and exclusion of a secondary cause of ILD such as for rheumatoid arthritis, sarcoidosis, occupational disorder or hypersensitivity pneumonitis. Serological tests may be required for hypersensitivity pneumonias.
There is no efficacious therapy for ILDs. Treatment of IPF remains elusive. Patients and clinicians are faced with four options: (i) no treatment, (ii) corticosteroids and cytotoxic agents, (iii) anti-fibrotic drugs, (iv) other miscellaneous agents.
Based on the evidence available immunosuppression with corticosteroids and cytotoxic agents is not helpful for IPF. These drugs are helpful in secondary ILDs such as CTD associated ILD, sarcoidosis and some other forms of IIP (NSIP, COP and DIP). Pirfenidone is the one agent which may provide some benefit in IPF. It is an anti-fibrotic drug which is shown to decrease the decline in lung function parameters. Several other drugs are also employed, but not very useful in improving the condition.
Most patients with IPF continue to experience an inexorable progression to death, with lung transplantation being the only measure shown to prolong survival. Currently, lung transplantation has been associated with improved lung function, exercise capacity, quality of life, and survival in this group of patients. The treatment is available at very few centres in India and the cost is prohibitive. Most importantly, there is very limited availability of organs. Lungs for transplantation can be retrieved only from a brain-dead individual with fully informed consent of the family following compliance of all the requisite legal and medical guidelines.
Thus, the primary objectives of treatment in IPF are essentially to provide symptomatic relief of symptoms, oxygen therapy for desaturation and pulmonary rehabilitation. One also needs to treat the complications which occur either secondary to the disease per se, or the toxicity of drugs.
Most forms of ILDs are progressive in nature. There is no permanent cure. Patient’s condition is likely to deteriorate with time. IPF is the worst form of ILD which carries a poor prognosis with an average survival of 3-5 years. Other ILDs have variable natural history which is modifiable with treatment.