A condition which may develop in both LUNGS (interstitial pulmonary fibrosis) or in part of one lung. Scarring and thickening of lung tissues occur as a consequence of previous lung inflammation, which may have been caused by previous PNEUMONIA, TUBERCULOSIS, an idiosyncratic reaction to medication or a connective tissue disorder but many cases have no known cause (‘idiopathic’). Symptoms include cough and breathlessness and diagnosis is confirmed with a chest X-ray. The patient's underlying condition should be treated, but the damage already done to lung tissue is usually irreversible. (See also ALVEOLITIS.) Some patients may benefit from a drug, pirfenidone, recently approved for use in Europe. Others may be recommended for lung transplantation.