Restrictive lung disease is any condition in which the elasticity of the lungs has been compromised. When lungs are stiff and unable to expand and contract as usual, then normal respiratory function is not possible. Restrictive lung disease is a general term to describe conditions that cause this stiffening. People with restrictive lung disease cannot fully fill their lungs with air. Their lungs are restricted from fully expanding. Restrictive lung disease most often results from a condition causing stiffness in the lungs themselves. In other cases, stiffness of the chest wall, weak muscles, or damaged nerves may cause the restriction in lung expansion. Some conditions causing restrictive lung disease are: Interstitial lung disease, such as idiopathic pulmonary fibrosis Sarcoidosis Obesity, including obesity hypoventilation syndrome Scoliosis Neuromuscular disease, such as muscular dystrophy or amyotrophic lateral sclerosis (ALS) The symptoms of restrictive lung disease can increase or decrease on a day-to-day basis. It is important to ask a qualified physician about the implications of symptoms that come and go. Restrictive lung disease is unlikely to go away, and usually gets worse without treatment. Even with treatment, the illness is not usually completely reversible.