Idiopathic pulmonary fibrosis is more common in smokers. The disease has a poor prognosis with median survival of 2 to 3 years. 

Diagnostic criteria include:

Major criteria

• exclusion of known cause of pulmonary fibrosis
• restrictive pattern in pulmonary function test
• bibasilar reticulation with minimal ground glass opacity
• negative bronchial lavage report for another disease

Minor criteria

• age >50 years
• dyspnea on exertion with insidious onset
• duration of illness>3 months
• Velcro Like respiratory crackles