ILD

ILD
Name	Interstitial Lung Disease
Synonyms	Diffuse Parenchymal Lung Disease
Field	Pulmonology, Rheumatology
Symptoms	Shortness of breath, Dry cough
Complications	Pulmonary hypertension, Respiratory failure
Duration	Chronic
Causes	Autoimmune disease, Occupational exposure, Drug reaction, Idiopathic
Risks	Smoking, Genetic predisposition, Environmental exposure
Diagnosis	High-resolution computed tomography, Pulmonary function test, Lung biopsy
Treatment	Corticosteroid, Immunosuppressive drug, Antifibrotic agent, Lung transplantation
Prognosis	Variable
Frequency	Variable by subtype

ILD. Interstitial lung disease represents a large, heterogeneous group of over 200 distinct disorders characterized by varying degrees of inflammation and fibrosis within the lung's interstitium. These conditions primarily affect the tissue and space surrounding the alveoli, leading to impaired gas exchange and progressive respiratory failure. The clinical course, underlying causes, and pathological findings can vary dramatically, making precise classification essential for effective management.

Definition and Classification

The term interstitial lung disease broadly encompasses a spectrum of disorders that cause scarring, or pulmonary fibrosis, of the lung parenchyma. A major classification divides these diseases into those with known causes and those that are idiopathic. The most common and severe idiopathic form is idiopathic pulmonary fibrosis, a relentlessly progressive condition with a distinct histopathological pattern of usual interstitial pneumonia. Other major categories include connective tissue disease-associated ILD, such as in rheumatoid arthritis or systemic sclerosis, and those related to occupational exposure like asbestosis or silicosis. Further classification relies on histopathological patterns observed via surgical lung biopsy, including nonspecific interstitial pneumonia and cryptogenic organizing pneumonia.

Causes and Risk Factors

Known causes of ILD are diverse and include chronic exposure to inorganic dusts like silica or beryllium, leading to pneumoconiosis. Numerous medications, such as chemotherapy agents like bleomycin and certain antiarrhythmic drugs like amiodarone, are well-documented culprits. A significant proportion of cases are associated with autoimmune and rheumatologic diseases, particularly systemic lupus erythematosus and Sjögren's syndrome. Environmental triggers, including exposure to mold or bird droppings causing hypersensitivity pneumonitis, are also important. Major risk factors include a history of cigarette smoking, certain genetic mutations like those in the MUC5B gene promoter, and possibly gastroesophageal reflux disease.

Signs and Symptoms

The clinical presentation of ILD is often insidious, with progressive exertional dyspnea being the most common and debilitating symptom. A persistent, non-productive dry cough is frequently reported and can be severe. Patients may exhibit bibasilar crackles on auscultation, often described as "Velcro-like" in quality. In advanced disease, signs of respiratory failure such as cyanosis and clubbing of the digits may develop. Systemic symptoms like fatigue, weight loss, and arthralgia are common, particularly when ILD is associated with an underlying connective tissue disease such as dermatomyositis.

Diagnosis

Diagnosis requires a multidisciplinary approach integrating clinical, radiological, and pathological data. High-resolution computed tomography of the chest is the cornerstone, revealing patterns like reticulation, honeycombing, and ground-glass opacity. Pulmonary function testing typically shows a restrictive ventilatory defect with reduced diffusing capacity for carbon monoxide. Serological testing for autoantibodies, including antinuclear antibody and rheumatoid factor, is crucial to identify associated autoimmune disease. In uncertain cases, obtaining tissue via bronchoscopy with transbronchial biopsy or surgical lung biopsy via video-assisted thoracoscopic surgery may be necessary for a definitive histopathological diagnosis.

Treatment and Management

Treatment strategies are highly dependent on the specific ILD diagnosis and underlying cause. For many inflammatory or autoimmune-related forms, first-line therapy often involves immunosuppression with prednisone combined with agents like azathioprine or mycophenolate mofetil. For idiopathic pulmonary fibrosis, antifibrotic drugs such as pirfenidone and nintedanib are approved to slow disease progression. Management of hypersensitivity pneumonitis centers on complete avoidance of the identified antigen. Supportive care includes pulmonary rehabilitation, supplemental oxygen therapy, and vaccination against influenza and Streptococcus pneumoniae. For eligible patients with advanced disease, referral for lung transplantation evaluation is critical.

Prognosis and Epidemiology

The prognosis of ILD varies immensely, ranging from stable, non-progressive forms to rapidly fatal conditions. Idiopathic pulmonary fibrosis carries a particularly poor prognosis, with a median survival of 3-5 years from diagnosis. Outcomes are generally better for forms like sarcoidosis or cryptogenic organizing pneumonia, which are often responsive to corticosteroid therapy. The overall incidence and prevalence are difficult to ascertain due to the diversity of disorders, but ILD as a group represents a significant cause of chronic respiratory morbidity. Epidemiological studies suggest increasing recognition, potentially due to improved diagnostic techniques like HRCT and an aging population.

Category:Respiratory diseases Category:Pulmonology