Pulmonary complications of HIV infection

Pneumocystis jirovecii pneumonia is a subacute, often hypoxic pneumonia in patients with CD4 counts below 200/mcL or comparable immunosuppression, diagnosed by organism visualization on induced sputum or bronchoalveolar lavage and treated with 21 days of high-dose trimethoprim-sulfamethoxazole plus adjunctive steroids when hypoxic.

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.

Community-acquired pneumonia is a lower respiratory tract infection acquired outside the hospital that is diagnosed by a compatible clinical syndrome plus a new infiltrate on chest imaging, risk-stratified with CURB-65 or the Pneumonia Severity Index to guide site of care, and treated with empiric antibiotics chosen by site of care and comorbidity, escalating to cover MRSA or Pseudomonas aeruginosa when risk factors are present.

Cryptococcal meningoencephalitis is the most common cause of fungal meningitis worldwide, driven by CNS dissemination of inhaled Cryptococcus in an immunosuppressed host, typically HIV with a CD4 count under 50; treatment is induction amphotericin B plus flucytosine, consolidation and maintenance fluconazole, and aggressive lowering of elevated intracranial pressure.

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.

Kaposi sarcoma is a human herpesvirus 8-associated vascular malignancy that presents as violaceous macules, papules, plaques, or tumors of the skin, mouth, gastrointestinal tract, or lungs, most often in HIV-associated, transplant-related, or classic elderly disease. Diagnosis is confirmed by biopsy. Every patient with HIV-associated Kaposi sarcoma starts or optimizes antiretroviral therapy, with liposomal doxorubicin 20 mg/m2 intravenously every 21 days added for extensive or visceral disease.

Non-Hodgkin lymphoma is a heterogeneous group of B-cell (about 85%) and T-cell lymphoid malignancies that spread noncontiguously and often involve extranodal sites, ranging from indolent follicular lymphoma to aggressive diffuse large B-cell lymphoma to highly aggressive Burkitt lymphoma. Diagnosis requires excisional or core biopsy with flow cytometry and cytogenetics, Ann Arbor staging with PET-CT, and treatment is subtype-specific, from observation to R-CHOP to intensive Burkitt regimens with aggressive tumor lysis and CNS prophylaxis.

Cytomegalovirus is a ubiquitous herpesvirus that is usually asymptomatic or causes a heterophile-negative mononucleosis-like illness in healthy hosts, but reactivates to cause retinitis, colitis, pneumonitis, or encephalitis in transplant recipients and patients with AIDS; treatment is systemic ganciclovir or valganciclovir, with foscarnet and cidofovir reserved for resistance or intolerance.

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.

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.

Opportunistic infection prophylaxis in HIV is a CD4-stratified framework: Pneumocystis prophylaxis at CD4 <200/mcL, Toxoplasma prophylaxis at CD4 <100/mcL in seropositive patients, and MAC prophylaxis at CD4 <50/mcL, each with a defined drug, dose, and CD4-recovery threshold for stopping. Antiretroviral therapy, started regardless of CD4 count, is the definitive prevention strategy and can make primary MAC prophylaxis unnecessary when started promptly.

HIV produces a CD4-count-stratified spectrum of GI disease, from candida, HSV, and CMV esophagitis to protozoal and mycobacterial diarrhea below CD4 100 and 50, AIDS cholangiopathy, and the AIDS-defining malignancies Kaposi sarcoma and non-Hodgkin lymphoma. Diagnosis matches the presenting syndrome and CD4 count to a syndrome-specific confirmatory test, and antiretroviral therapy is the cornerstone of management for nearly every entity in this spectrum.

HIV infection produces cytopenias, coagulation abnormalities, and B-cell lymphomas through mechanisms that shift with CD4 count, from immune-mediated peripheral destruction and drug toxicity at higher CD4 counts to opportunistic marrow infiltration and aggressive lymphoma once CD4 falls below 100-50/mcL. Antiretroviral therapy is the single most effective intervention across nearly all of these complications, and management otherwise follows the specific cytopenia or malignancy identified after excluding drug causes, nutritional deficiency, and coinfection.