Lung parenchyma has no power of regeneration. Hence, destructive lesions lead on to fibrosis. Fibrosis of the lung parenchyma may take three forms-replacement fibrosis focal fibrosis, and interstitial fibrosis.
Replacement fibrosis
In this form fibrous tissue is laid down over areas of lung destruction. The fibrosis is often localized and its extent depends on the extent of parenchymal destruction. Coarse causes consist of developed pulmonary tuberculosis, bronchiectasis, lung abscess, pulmonary infarcts, pneumonias, atelectasis, fungal infections, pleural diseases such as persisting pleural effusion and empyema, response to foreign materials such as lipoid pneumonia, and irradiation of the lung.
Foal fibrosis
This is seen in pneumoconiosis such as silicosis. The extent of fibrosis may vary from small nodular lesions to ample areas (progressive weighty fibrosis).
Interstitial fibrosis
This is the end supervene of interstitial lung disease. Interstitial fibrosis may supervene from persisting pulmonary edema (occurring in mitral stenosis), allergic alveolitis, connective tissue disorders such as progressive systemic sclerosis and rheumatoid disease, cryptogenic fibrosing alveolitis, radiation injury to the lung, sarcoidosis, asbestosis, and idiopathic pulmonary hemosiderosis. In this form, interstitial fibrosis and emphysematous changes coexist.
Clinical features
Replacement fibrosis: The most Coarse cause in is persisting pulmonary tuberculosis. The upper lobes are affected more frequently. The chest is asymmetrical with flattening of the affected side, drooping of the shoulder and diminution of movement. Trachea and mediastinal structures are pulled towards the same side, unless they were already fixed by pre-existing disease. The percussion note is diminished. Vocal fremitus and vocal resonance depend upon the severity of fibrosis. In ample fibrosis they are reduced. If a major bronchus lies subjacent to the fibrotic area the vocal fremitus and resonance are increased and breath sounds become bronchial. In ample fibrosis, especially fobrothorax, the breath sounds are considerably diminished. Adventitious sounds may be heard and these are variable. Symptoms and hemodynamic disturbances depend upon the extent of pulmonary lesions and the cause.
Replacement fibrosis has to be noteworthy from pulmonary collapse in which there may be ipsilateral shift of midline structures. Pulmonary collapse is commonly of shorter duration and the underlying cause may be evident.
Other forms of fibrosis: Since these are generalized, affecting both lungs, there is no marked shift of midline structures. The symptoms are those of ventilatory and diffusive defects predominantly characterized by dyspnea, cyanosis, frequwent respiratory infections, and persisting cor pulmonale. Physical exam may review gross clubbing, tachypnea, cyanosis, and diminished respiratory movements. Breath sounds are diminished. Diffuse rales (Crackles) which persist after coughing are characteristic. X-ray of the chest may show generalized loss of translucency and increased reticulation. Cardiac findings consist of right ventricular enlargement and hypertrophy, and lound pulmonic second sound indicating pulmonary hypertension.
Causes and prognosis
Replacement fibrosis does not commonly strengthen further. The course of the disease and longieivity depend on the extent of the lesion, occurrence of secondary infections and the improvement of cor pulmonale. In general, with uncostly care, localized fibrosis is compatible with prolonged survival. Diffuse interstitial fibrosis is progressive in most cases and life is needful shortened. Death is due to respiratory failure or cardiac failure.
Management
General measures consist of the avoidance of smoking, medicine of intercurrent infections, allowance of weight and respiratory exercises. Definite medicine for the underlying cause should be given, if there are signs of action of the disease. Diffuse interstitial fibrosis may riposte to corticosteroids or immunosuppressant drugs. But the results are not encouraging. Cardiac complications are treated suitably.
