Solitary pulmonary nodule

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.

Tuberculosis, caused by Mycobacterium tuberculosis, remains a leading global cause of infectious death and presents as latent infection, primary/secondary pulmonary disease, or extrapulmonary and disseminated (miliary) disease. Diagnosis rests on AFB smear, NAAT, and mycobacterial culture (the gold standard), and drug-susceptible active disease is treated with a four-drug regimen (isoniazid, rifampin, pyrazinamide, ethambutol) for 2 months followed by isoniazid plus rifampin for 4 to 7 months.

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.

Histoplasma capsulatum is an endemic dimorphic fungus, acquired by inhalation of conidia in the Mississippi and Ohio River valleys and other endemic regions, that most often causes asymptomatic or mild pulmonary infection but can disseminate in immunosuppressed hosts; diagnosis rests on the Histoplasma urinary antigen assay and treatment is itraconazole for mild to moderate disease or liposomal amphotericin B followed by itraconazole for severe or disseminated infection.

Granulomatosis with polyangiitis (GPA) is an antineutrophil cytoplasmic antibody (ANCA)-associated necrotizing granulomatous vasculitis of the upper airway, lower airway, and kidney, most often with cytoplasmic ANCA (c-ANCA) targeting proteinase 3 (PR3). Diagnosis rests on the clinical triad, ANCA serology, and tissue biopsy showing pauci-immune vasculitis, and treatment begins with high-dose glucocorticoids plus rituximab or cyclophosphamide for organ-threatening disease, followed by rituximab or azathioprine maintenance.

Eosinophilic granulomatosis with polyangiitis (EGPA) is the rarest antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis, defined by a three-phase course of late-onset asthma and rhinosinusitis, then peripheral and tissue eosinophilia, then small- and medium-vessel vasculitis with mononeuritis multiplex. ANCA is positive in only 40 to 60 percent of patients, cardiac involvement drives most mortality, and treatment is glucocorticoids alone for non-organ-threatening disease, glucocorticoids plus cyclophosphamide or rituximab for organ-threatening disease, and mepolizumab as steroid-sparing therapy.

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.

Chronic obstructive pulmonary disease is a persistent, usually progressive airflow obstruction driven mainly by cigarette smoke, confirmed by a postbronchodilator FEV1/forced vital capacity (FVC) ratio below 0.70 and staged by GOLD spirometric grade plus symptom/exacerbation group. Maintenance management is a stepwise ladder of smoking cessation, long-acting bronchodilators, add-on inhaled glucocorticoid, roflumilast, or azithromycin for frequent exacerbators, long-term oxygen for resting hypoxemia, and vaccination, with acute exacerbations managed as a separate protocol.

Invasive aspergillosis is an angioinvasive mold infection of neutropenic and immunosuppressed hosts that begins in the respiratory tract and disseminates hematogenously, diagnosed with CT, galactomannan, and biopsy, and treated first-line with voriconazole.