Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (578 page)

   Advanced cardiopulmonary exercise testing is the most accurate way to diagnose dyspnea. Many standard diagnostic tests for shortness of breath, including noninvasive cardiopulmonary testing, EKG, CT, and pulmonary function testing, provide inconclusive results or misdiagnosis.

   There are relatively few blood tests that are necessary in the initial evaluation of a patient with dyspnea. Hemoglobin and hematocrit to exclude anemia, and ABG measurements may be a value in managing severe underlying cardiopulmonary disease.
D
-Dimer is a component of the evaluation of patients with suspected PE. For patients with acute dyspnea, especially those who come to ER, BNP or NT-pro BNP may be useful for the evaluation of heart failure as the cause of dyspnea.

PULMONARY DISEASES ASSOCIATED WITH DYSPNEA

INFECTIOUS RESPIRATORY SYNDROMES ASSOCIATED WITH DYSPNEA

LOWER RESPIRATORY TRACT SYNDROMES

BRONCHIOLITIS

   Definition

Bronchiolitis is an inflammatory disease of the small airways and may be caused by a variety of infectious or noninfectious conditions. Infectious bronchiolitis is usually caused by viral pathogens and is primarily a disease of infants and young children.
Respiratory syncytial virus
(RSV) is the primary cause of bronchiolitis (approximately 75%), especially severe bronchiolitis that requires medical attention or hospitalization. Rhinovirus and other respiratory viral pathogens may causes bronchiolitis, including parainfluenza virus (type 3), human metapneumovirus, influenza virus, and adenovirus. Monoclonal antibody therapy or antiviral therapies may be considered for infants with severe RSV infection.

   Who Should Be Suspected?

   Bronchiolitis usually occurs in the fall and winter, during the peak times of circulation of seasonal respiratory viruses. The peak incidence is in children 2–6 months of age. Children with cardiac or pulmonary disease, immunodeficiency, and history of premature birth are at increased risk for serious disease.

   There may be nonspecific findings of viral respiratory infection, like rhinitis. The major clinical manifestation is air trapping due to expiratory obstruction. Wheezing is common.

   Infants present with an increased respiratory rate and obvious difficulty breathing marked by nasal flaring. Severely affected infants may be cyanotic. Fever is not a prominent feature.

   Diagnostic and Laboratory Findings

Diagnostic studies are not required for the management of most infants with clinical signs and symptoms of bronchiolitis; testing should be reserved for patients for whom results are likely to affect management decisions, like decisions regarding the need for antibiotic therapy.

Chest radiograph
: May be indicated to rule out pneumonia.

Core labs
: ABGs may be monitored in infants with severe disease. Core laboratory tests are usually normal, although fluid status must be monitored carefully because of the risk of dehydration due to tachypnea.

Molecular tests
: Commercially available assays, which include testing for a panel of respiratory viruses, are recommended for establishing a specific diagnosis. These assays show improved sensitivity and specificity compared to viral culture or antigen testing; they also enable detection of a broader range viruses.

Antigen detection
: Detection of specific antigen in nasopharyngeal secretions is available for several relevant viruses, like influenza viruses A and B, RSV, and human metapneumovirus. Assays based on DFA staining are useful for evaluation of specimen quality and have shown improved sensitivity compared to IFA assays. Because of the rapid turnaround time and reasonable specificity, antigen detection assays may be helpful in establishing a diagnosis. Infection cannot be ruled out by antigen assays because of their limited sensitivity and the limited scope of viruses tested.

Culture
: Most of the relevant viruses may be isolated by viral culture, but turnaround time is slow. Therefore, viral culture is usually not helpful for acute clinical management.

LEGIONELLA INFECTION (LEGIONNAIRES DISEASE)

   Definition

Legionella
species have been documented as a relatively common cause of communityacquired and nosocomial pneumonia. Infection is usually caused by
Legionella pneumophila
, a fastidious aerobic gram-negative bacillus, but several other species may also cause disease. Respiratory infections are the primary manifestation of legionellosis.

   Who Should Be Suspected?