Pulmonary presentations are among the most common reasons for emergency department visits by HIV-infected patients. —I2 Presenting complaints frequently are nonspecific and include cough, hemoptysis, shortness of breath, and chest pain. Emergency department evaluation should be directed toward determining the likely diagnosis, since early treatment may have a significant impact on morbidity and mortality rates. Appreciation of the epidemiologic characteristics and common findings associated with various pathogens can assist the emergency physician in arriving at an appropriate differential and working diagnosis, leading to sound treatment and disposition decisions.
The most common causes of pulmonary abnormalities in HIV-infected patients include community-acquired bacterial pneumonia, PCP, Mycobacterium tuberculosis (MTB), CMV, Cryptococcus neoformans, Histoplasma capsulatum, and neoplasms.
In addition to the history and physical examination, evaluation of patients with pulmonary complaints may be assisted by pulse oximetric analysis, arterial blood-gas determination, sputum culture, Gram staining, acid-fast staining, blood culture, and chest x-ray. Pulmonary radiographic findings are helpful in determining likely causes (T.a.b!e...,.1..3.9.-.6). Admission should be considered for patients with new-onset pulmonary symptoms, especially those with hypoxia. Decisions regarding patients with known pulmonary involvement are based on comparison to baseline status, the effectiveness of ongoing or previous treatment, and the individual's ability to obtain outpatient follow-up. Specific symptoms are discussed below with selected common causes.
TABLE 139-6 Chest Radiographic Abnormalities: Differential Diagnosis in AIDS Patients
Despite substantial decreases in the incidence of PCP due to effective prophylaxis, it continues to be the most common opportunistic infection among AIDS patients.
Approximately 70 percent of HIV-infected patients will acquire PCP at some time during their illness, and PCP is often the initial opportunistic infection that establishes the diagnosis of AIDS. This disease is the most frequent serious complication of HIV infection in the United States and the most common identifiable cause of death in patients with AIDS. The classic presenting symptoms of PCP are fever, cough (typically nonproductive), and shortness of breath (progressing from being present only with exertion to being present at rest).
Symptoms are often insidious and accompanied by fatigue. Chest x-rays most often show diffuse interstitial infiltrates ( T§b]e.,..139!,-,6). Although typical radiographic findings occur in up to 80 percent of cases, negative x-rays are reported in 15 to 20 percent of patients with PCP. 13 In patients with nondiagnostic x-ray findings and signs and symptoms suggestive of PCP, further testing should be pursued. The lactate dehydrogenase (LDH) level is elevated in patients with PCP, but the test for LDH has relatively low sensitivity and specificity, making its use in the emergency department impractical. Arterial blood-gas analysis usually demonstrates hypoxemia and an increase in the alveolar-arterial (A-a) gradient. (Early PCP should be suspected if a patient demonstrates a decrease in pulse oximetric values with exercise.) Presumptive diagnosis of PCP is often assumed in the emergency department if there is hypoxia without any other explanation. Inpatient diagnostic testing may include bronchoscopy with lavage, biopsy, and culture or examination of induced sputum by indirect immunofluorescence using monoclonal antibodies.
Initial therapy for PCP is trimethoprim-sulfamethoxazole (TMP-SMX) TMP 15 mg/kg/day and SMX 75 mg/kg/day) either orally or intravenously for 3 weeks in two or three divided doses [typical oral dosage 2 double strength (DS) tid]. Adverse reactions (most commonly rash, fever, and neutropenia) occur in up to 65 percent of AIDS patients. Pentamidine isothionate 4 mg/kg/day is one of a number of effective alternative agents. Steroid therapy should be instituted for patients with a Pa o2 less than 70 mmHg or an alveolar-arterial gradient greater than 35.14 The usual regimen is oral prednisone 40 mg bid for 5 days, then 40 mg qd for 5 days, and then 20 mg qd for an additional 11 days. Seventy percent of patients will have reinfection within 18 months. Prophylactic therapy is an important step in preventing reinfection and has also been shown to reduce the risk of developing bacterial pneumonia; oral TMP-SMX 1 DS qd is the preferred agent. Prophylaxis is also recommended in all patients with CD4 counts below 200 cells/pL. Repeat infections may be less responsive to therapy.
The incidence of Mtb is increasing, particularly among the homeless, institutionalized, immigrant, and intravenous-drug-using populations. Reactivation of prior infection is common, and there is a much greater risk of direct progression of disease from recently acquired infection. The incidence of tuberculosis (TB) in the AIDS population is estimated to be 200 to 500 times that in the general population. 15 Prevalence studies demonstrate significant regional variations, attributed to both the demographic characteristics of the populations and the efficacy of local public health control measures.
Clinical manifestations of TB in HIV infection vary significantly according to the severity of immunosuppression. Whereas PCP does not occur until the CD4 count is approximately 200 cells/pL, TB frequently occurs in patients with CD4 counts of 200 to 500 cells/pL. Classic pulmonary manifestations include cough with hemoptysis, night sweats, prolonged fevers, weight loss, and anorexia. With worsening immunosuppression, atypical and extrapulmonary manifestations are more common. Frequent sites of dissemination are peripheral lymph nodes, bone marrow, and the urogenital system. Classic upper lobe involvement and cavitary lesions are less common, particularly among late-stage AIDS patients.13 Negative purified protein derivative (PPD) TB test results are frequent among AIDS patients due to immunosuppression. Definitive diagnosis may be made by stain and culture of sputum, although in some cases bronchoscopy with biopsy may be required.
In the emergency department, physicians should maintain a high index of suspicion for TB among HIV-infected patients with pulmonary symptoms due to the high rates of person-to-person transmission. Immediate isolation should be instituted until the diagnosis is ruled out. Specific procedures for ruling out TB vary by region and site and have been found to be inadequate in some emergency departments.16 Any patient identified as high risk based on clinical presentation should be placed in isolation, with the decision for further isolation based on results of chest x-ray and detailed historical and clinical information. Current treatment guidelines recommend a four-drug initial empiric therapy (T§b.!e...1„39z5). Multidrug-resistant TB remains an issue of concern and should increase the awareness of the need for early isolation. All HIV-infected patients with positive PPD test results should receive prophylaxis with isoniazid for 1 year.
Nonopportunistic bacterial pneumonias are the most common pulmonary infections in HIV-infected patients. Common pathogens include Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus aureus. Productive cough, leukocytosis, and the presence of a focal infiltrate suggest bacterial pneumonia, especially in those with earlier-stage disease. The response to empiric therapy tends to be good; a specific diagnosis can be established by Gram staining and culture.
Patients with severe immunosuppression are predisposed to disseminated fungal infections, such as C. neoformans and Aspergillus fumigatus. Other noninfectious disorders of the lung seen in HIV-infected patients include neoplasms (e.g., Kaposi's sarcoma) and lymphocytic interstitial pneumonitis. CMV or Mycobacterium avium complex are unlikely unless the CD4 count drops below 50 cells/pL.
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