Restrictive lung disease | Respiratory system | Pathology

Restrictive lung diseases, on the other hand, are caused by decreased lung volumes, without any obstruction to airflow, due to pathology in the lung parenchyma, chest wall or pleura. It is seen in interstitial lung disease, morbid obesity, scoliosis, kyphosis, ankylosing spondylitis and neuromuscular disorders like Guillain-Barre syndrome, myasthenia gravis, muscular dystrophy and ALS.

Categories of restrictive lung diseases

Chest wall disorders	Kyphoscoliosis, morbid obesity, pleural disorders
Lung parenchymal disorders	Interstitial lung diseases (pneumoconiosis, sarcoidosis, rheumatoid arthritis, collagen vascular diseases etc.)

Interstitial lung disease (ILD) encompasses more than 200 different disorders. Fibrosis is seen as a result of inflammation in ILD. What triggers the initial inflammation may not be always known but exposure to bleomycin, asbestos, silica, tobacco smoke, wood dust, mold, environmental allergens and autoimmune diseases predispose to ILD. Cytokines and proteases released by activated inflammatory cells and ROS damage the alveolar cells, which is followed by proliferation of type II pneumocytes and repair by fibrosis. The lung compliance is decreased while the recoil is increased. Clinical presentation is with gradually progressive dry cough, dyspnea, tachypnea, cyanosis and late inspiratory crackles and . On gross examination the lung is scarred and scattered cystic air spaces are seen as a “honeycombing” pattern. CxR shows diffuse bilateral reticulonodular opacities.

Common causes of Drug induced ILD

Amiodarone
Methotrexate
Nitrofurantoin
Rituximab
Bleomycin
ACE inhibitors
Busulfan
Cabergoline

Pneumoconiosis are a group of mostly occupational diseases that result from occupational exposure to inhaled dust that results in ILD. Inhaled particles <1 micrometer reach the alveoli and incite an inflammatory response in susceptible individuals.

Occupational exposure and corresponding pneumoconiosis

Occupational exposure	Type of pneumoconiosis
Coal dust	Coal worker’s pneumoconiosis, Caplan’s syndrome, progressive massive fibrosis
Silica	Silicosis, Caplan’s syndrome
Asbestos	Asbestosis
Beryllium	Berylliosis
Mouldy hay, grain	Farmer’s lung (Saccharopolyspora rectivirgula)
Molasses, sugarcane (bagasse)	Bagassosis (T.vulgaris)
Cotton, hemp, flax	Byssinosis, cotton worker’s lung
Bird droppings, feathers	Bird fancier’s lung
Silo-Filler’s disease	Exposure to NO2 gas in silo causes pulmonary edema

1) Coal worker’s pneumoconiosis (CWP): CWP develops in coal miners over 20-30 years of exposure. Alveolar macrophages and cytokines IL 1, TNF and PDGF are implicated in inflammation and fibrosis. Miners are at higher risk of TB and RA, but risk is the same as the general population for lung cancer. Presents with cough and black sputum, dyspnea, cor pulmonale. Two types are seen:

Simple CWP: scattered foci of dust-laden macrophages with surrounding dilated air spaces are seen, minimal fibrosis, mostly in upper zones. CxR shows round nodular opacities with occasional calcification.

Progressive massive fibrosis or complicated CWP: larger areas than above, necrotic areas, severe fibrosis obliterating the respiratory bronchiole and vessels, markedly dilated alveoli. CxR shows large opacities which may be surrounded by cystic spaces.

Caplan’s syndrome: Rheumatoid arthritis plus CWP or pneumoconiosis is Caplan’s syndrome; rheumatoid nodules seen in the lung, microscopically as firm nodules with inflammatory exudate of mononuclear cells and fibroblasts, cavitation and necrosis.

Anthracosis is a common finding in city dwellers that results from the deposition of anthracotic or carbon dust pigment in the lungs, from pollution and cigarette smoke. Pigmented macrophages called “dust cells” can be seen in alveoli, respiratory bronchioles and draining lymph nodes in anthracosis.