Interstitial lung disease

Idiopathic pulmonary fibrosis is a chronic, progressive fibrosing lung disease of unknown cause defined by a usual interstitial pneumonia (UIP) pattern, presenting with progressive dyspnea, dry cough, bibasilar Velcro crackles, and clubbing in older smokers. A definite UIP pattern on high-resolution CT confirms the diagnosis without biopsy; management centers on antifibrotic therapy (pirfenidone or nintedanib), oxygen, and early lung transplant referral, since corticosteroids are not indicated and median survival is 3 to 5 years.

Hypersensitivity pneumonitis is a mixed type III/IV immune reaction to repeated inhalation of an organic antigen in a sensitized host, producing noncaseating granulomas and bronchiolocentric inflammation. Removal of the offending antigen is the essential first step in treatment; glucocorticoids are added for significant hypoxemia or symptom burden, and unremitting exposure can progress to fibrotic lung disease indistinguishable from idiopathic pulmonary fibrosis.

Sarcoidosis is a multisystem granulomatous disease of unknown cause defined by noncaseating granulomas, most commonly involving the lungs and hilar lymph nodes. Most patients are asymptomatic or have a self-limited course staged by chest radiograph; symptomatic organ-threatening disease is treated with systemic glucocorticoids, with methotrexate or another steroid-sparing agent added for glucocorticoid-refractory or glucocorticoid-intolerant disease.

Rheumatoid arthritis is a chronic systemic autoimmune disease causing symmetric small-joint polyarthritis of the hands and feet that spares the distal interphalangeal joints, with morning stiffness over an hour. Diagnosis combines the ACR/EULAR classification criteria with rheumatoid factor, anti-CCP antibody, and radiographs. Treat-to-target management anchors on methotrexate, escalating to a biologic or targeted synthetic disease-modifying antirheumatic drug when remission is not reached.

Dermatomyositis is a complement-mediated inflammatory myopathy causing symmetric proximal weakness with pathognomonic skin findings, heliotrope rash and Gottron papules, that separate it from polymyositis. It carries a 3- to 12-fold increased malignancy risk and a distinct interstitial lung disease burden that drive workup and therapy. First-line treatment is high-dose prednisone with an early steroid-sparing agent.

Polymyositis is an idiopathic inflammatory myopathy causing symmetric, subacute proximal muscle weakness with no rash, driven by endomysial CD8-positive T-cell invasion of non-necrotic, MHC class I-expressing muscle fibers. It is a diagnosis of exclusion confirmed by muscle biopsy, and first-line treatment is high-dose prednisone with a steroid-sparing agent such as methotrexate or azathioprine started concurrently.

Sjogren syndrome is a systemic autoimmune exocrinopathy in which lymphocytic infiltration of the lacrimal and salivary glands causes keratoconjunctivitis sicca and xerostomia, occurring alone (primary) or alongside another rheumatologic disease such as rheumatoid arthritis or lupus (secondary). Diagnosis combines the anti-Ro (SSA) and anti-La (SSB) antibody panel, objective dryness testing, and labial salivary gland biopsy under the 2016 ACR/EULAR classification criteria. Management centers on sicca-directed therapy, pilocarpine or cevimeline for xerostomia and topical cyclosporine for keratoconjunctivitis, with hydroxychloroquine or immunosuppression for extraglandular disease.

Silicosis is a fibrotic occupational lung disease caused by inhaling crystalline silica dust, producing upper-zone nodular opacities and progressive dyspnea in exposed workers. Diagnosis rests on a compatible exposure history plus a characteristic imaging pattern. No agent reverses the fibrosis, so management is supportive: exposure cessation, oxygen for hypoxemia, vaccination, isoniazid prophylaxis for latent tuberculosis, and transplant evaluation for advanced disease.

Pulmonary hypertension is a resting mean pulmonary artery pressure of 20 mmHg or greater on right heart catheterization, classified into five WHO groups by mechanism. Diagnosis requires screening echocardiography followed by confirmatory right heart catheterization, and management is group-specific, with PAH-targeted vasodilator therapy reserved for group 1 disease.

Cor pulmonale is right ventricular structural and functional impairment caused by group 3 pulmonary hypertension from chronic lung disease or hypoxemia. Diagnosis rests on echocardiographic screening confirmed by right heart catheterization, and management centers on treating the underlying lung disease, correcting hypoxemia, and cautious diuresis.

GERD is retrograde reflux of gastric contents into the esophagus causing heartburn and regurgitation, diagnosed clinically and confirmed by response to an empiric PPI trial, with endoscopy reserved for alarm features or refractory symptoms. Management proceeds from lifestyle measures through an 8-week once-daily PPI trial, dose escalation or agent switch for partial response, and fundoplication for medication-refractory or regurgitation-predominant disease.

Lung cancer is the leading cause of cancer death worldwide, split into non-small cell lung cancer (NSCLC, 80% of cases: adenocarcinoma, squamous cell, large cell) and small cell lung cancer (SCLC, 10-15%), both driven overwhelmingly by cigarette smoking. Diagnosis requires tissue histopathology, staging drives treatment (TNM staging for NSCLC, limited versus extensive stage for SCLC), and management ranges from lobectomy in early-stage disease through concurrent chemoradiation and consolidation immunotherapy in locally advanced disease to targeted tyrosine kinase inhibitors, immune checkpoint inhibitors, or platinum-based chemotherapy in metastatic disease.