Section 6.2: Restrictive & Interstitial Lung Diseases

Restrictive and Interstitial Lung Diseases: Diagnosis, Staging, and Management

Restrictive lung diseases are characterized by a reduction in total lung capacity (TLC < 80% predicted). On spirometry, they present with a normal or elevated forced expiratory volume in one second to forced vital capacity ratio (FEV1/FVC >= 0.70, often > 0.80) and a symmetrical reduction in both FEV1 and FVC. The diffusing capacity of the lung for carbon monoxide (DLCO) is crucial to differentiate intrinsic parenchymal pathologies (characterized by a low DLCO due to alveolar-capillary membrane thickening) from extrinsic chest wall or neuromuscular disorders (characterized by a normal or elevated DLCO because the lung tissue itself is healthy).

Idiopathic Pulmonary Fibrosis (IPF)

Idiopathic pulmonary fibrosis is a chronic, progressive, fibrosing interstitial pneumonia of unknown etiology that occurs primarily in older adults (typically males > 60 years old) with a history of cigarette smoking. Patients present with insidious, progressive exertional dyspnea and a chronic, nonproductive cough. Physical examination characteristically reveals dry, velcro-like end-inspiratory crackles at both lung bases and digital clubbing.

The diagnostic modality of choice is high-resolution computed tomography (HRCT) of the chest. A diagnosis of IPF requires the identification of a Usual Interstitial Pulmonary (UIP) pattern on HRCT. The key radiographic features of a UIP pattern include subpleural and basal-predominant reticular abnormalities, traction bronchiectasis (representing airway dilation from surrounding parenchymal traction), and honeycombing (clusters of cystic air spaces with thick walls). If the clinical presentation and HRCT findings are classic for a UIP pattern, a surgical lung biopsy is unnecessary and contraindicated due to procedural risks. When HRCT findings are indeterminate, a surgical lung biopsy may be performed, showing spatial and temporal heterogeneity: areas of dense collagenous fibrosis and honeycombing alternating with fibroblastic foci (representing active fibrogenesis) and normal lung tissue.

Management: There is no cure for IPF, and the primary goal is slowing disease progression.

• Antifibrotic Therapy: Nintedanib (a multi-tyrosine kinase inhibitor) and pirfenidone (an inhibitor of transforming growth factor-beta [TGF-b]) are first-line agents proven to slow the rate of decline in forced vital capacity (FVC).
• Avoid Immunosuppression: Systemic corticosteroids and immunosuppressive agents (such as azithromycin or azathioprine) are contraindicated for routine use, as clinical trials (specifically the PANTHER-IPF trial) demonstrated increased mortality and hospitalization with their use.
• Definitive Treatment: Lung transplantation is the only curative intervention and must be discussed early in the disease course. Supportive care includes supplemental oxygen for hypoxemia, pulmonary rehabilitation, and treatment of gastroesophageal reflux disease (GERD), which is highly prevalent and associated with microaspiration-induced fibrosis progression.

Sarcoidosis: Diagnosis and Staging

Sarcoidosis is a systemic inflammatory disease of unknown etiology characterized by the accumulation of noncaseating granulomas in affected organs, most commonly the lungs and intrathoracic lymph nodes. It occurs more frequently in young adults, with a higher prevalence and severity in African American females.

Clinical presentations range from asymptomatic incidental findings to severe multiorgan disease. Extrapulmonary manifestations are common and clinically significant:

• Skin: Erythema nodosum (painful, erythematous nodules on the shins, representing a reactive panniculitis associated with a favorable prognosis) and lupus pernio (violaceous, indurated plaques on the nose, cheeks, and ears, associated with chronic disease).
• Eyes: Anterior or posterior uveitis, which can lead to blindness and requires screening.
• Nervous System: Facial nerve (cranial nerve VII) palsy is the most common neurological manifestation.
• Heart: Cardiac sarcoidosis can present with complete heart block, ventricular arrhythmias, congestive heart failure, or sudden cardiac death.
• Heerfordt Syndrome: A specific manifestation consisting of uveitis, parotid gland swelling, facial palsy, and fever.
• Lofgren Syndrome: An acute presentation characterized by the triad of bilateral hilar adenopathy, erythema nodosum, and migratory polyarthritis, accompanied by fever.

Diagnostic Approach:

1. Biopsy: Demonstration of noncaseating granulomas on tissue biopsy (typically obtained via transbronchial needle aspiration [TBNA] during bronchoscopy) is the diagnostic standard. Alternative biopsy sites include accessible skin lesions (excluding erythema nodosum, which is non-granulomatous) or palpable lymph nodes. Infections (such as tuberculosis and histoplasmosis) must be excluded with negative acid-fast bacilli and fungal stains/cultures.
2. Lofgren Syndrome Exception: Biopsy is not required if the patient presents with the complete, classic triad of Lofgren syndrome, as the diagnostic specificity is greater than 95%.
3. Laboratory Findings: Elevated serum calcium and urinary calcium (due to autonomous production of 1-alpha-hydroxylase by alveolar macrophages, which converts vitamin D to its active form, 1,25-dihydroxyvitamin D). Elevated angiotensin-converting enzyme (ACE) levels are common but lack sensitivity and specificity.
4. Radiographic Staging (Scadding Scale):
   • Stage I: Bilateral hilar adenopathy (BHA) alone.
   • Stage II: BHA plus parenchymal infiltrates.
   • Stage III: Parenchymal infiltrates without BHA.
   • Stage IV: Pulmonary fibrosis (honeycombing) and architectural distortion.

Treatment: Asymptomatic Stage I or mild Stage II sarcoidosis does not require therapy, as spontaneous resolution occurs in up to 80% of patients. Treatment with systemic corticosteroids (oral prednisone) is indicated for patients with disabling respiratory symptoms, progressive loss of lung function, or significant extrapulmonary organ involvement (cardiac, neurologic, ocular, renal, or persistent hypercalcemia). Second-line agents include methotrexate, azathioprine, and TNF-alpha antagonists (infliximab).

Hypersensitivity Pneumonitis

Hypersensitivity pneumonitis (HP) is an immunologically mediated inflammatory disease of the lung parenchyma and terminal airways caused by repeated inhalation of organic dusts or occupational antigens. It involves a combination of Type III (immune complex-mediated) and Type IV (cell-mediated) hypersensitivity reactions. Common antigens include:

• Thermophilic actinomycetes: Found in moldy hay (Farmer’s lung) or compost.
• Avian proteins: Found in bird droppings or feathers (Bird fancier’s lung).
• Fungal spores: Found in contaminated humidifiers (Humidifier lung).

Clinical Subtypes:

• Acute HP: Presents 4-8 hours after intense antigen exposure with abrupt onset of fever, chills, nonproductive cough, dyspnea, and bilateral bibasilar crackles. It resolves spontaneously within 12-48 hours upon removal from the source.
• Chronic/Fibrotic HP: Results from low-grade, continuous antigen exposure over months to years, presenting with progressive exertional dyspnea, fatigue, weight loss, and digital clubbing.

Diagnostics: Chest HRCT demonstrates centrilobular ground-glass nodules, mosaic attenuation (representing air trapping on expiratory views), and in chronic stages, upper-lobe predominant fibrosis. Bronchoalveolar lavage (BAL) is highly specific, showing a marked lymphocytosis (often > 50% lymphocytes) with a decreased CD4/CD8 ratio (typically < 1.0). Serum precipitating IgG antibodies confirm exposure but do not prove active disease.

Management: Complete antigen avoidance is the single most critical intervention. For acute flares or progressive chronic disease, systemic corticosteroids are utilized to accelerate clinical improvement, though they do not alter the long-term fibrotic prognosis.

Pneumoconioses

Pneumoconioses are occupational lung diseases caused by the inhalation and tissue reaction to inorganic mineral dusts:

1. Silicosis: Inhalation of free crystalline silica dust (sandblasting, stone cutting, mining). HRCT shows small, nodular opacities in the upper lobes and calcification of the rim of hilar lymph nodes (eggshell calcifications). Silicosis impairs macrophage function by disrupting lysosomes after phagocytosis of silica particles, rendering the patient highly susceptible to intracellular pathogens. All patients with silicosis must be screened for tuberculosis (latent or active) using an interferon-gamma release assay (IGRA) or a tuberculin skin test (TST).
2. Coal Worker’s Pneumoconiosis (CWP): Inhalation of coal dust, leading to coal macules in the upper lobes. Caplan syndrome refers to the co-occurrence of CWP (or silicosis) and rheumatoid arthritis, presenting with rapidly expanding peripheral lung nodules.
3. Asbestosis: Inhalation of asbestos fibers (shipbuilding, construction, insulation work). Clinically presents 20-30 years after exposure with lower-lobe predominant interstitial fibrosis. Radiography shows pleural plaques (well-demarcated, calcified plaques along the bilateral lower chest wall and diaphragm). Ferruginous bodies (asbestos fibers coated with iron-protein complexes) are seen on histology. Complications include bronchogenic carcinoma (the most common malignancy in exposed individuals, with a highly synergistic risk in smokers) and malignant pleural mesothelioma (a rare but highly specific tumor of the pleura).
4. Berylliosis: Beryllium exposure (aerospace, electronics manufacturing). Presents with noncaseating granulomas and hilar adenopathy, mimicking sarcoidosis. Diagnosed by the Beryllium Lymphocyte Proliferation Test (BeLPT). Responds to corticosteroids.