Mycoplasmal Pneumonia Workup

Updated: Aug 11, 2016
  • Author: Michael Joseph Bono, MD, FACEP; Chief Editor: Ryland P Byrd, Jr, MD  more...
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Workup

Approach Considerations

Laboratory tests are generally of limited benefit in mycoplasmal pneumonia, as they tend to be nonspecific or within the normal range. For example, elevated erythrocyte sedimentation rates (ESR) may be present but are nonspecific. The white blood cell (WBC) count is generally not helpful in this condition because results may be normal or elevated, and, although hemolytic anemia has been described, it is rare.

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Radiography

Chest radiographic findings vary, but abnormalities are usually more striking than the findings upon physical examination. Bronchopneumonia often appears as patchy consolidation and involves a single lower lobe, although lobar consolidation is rare. Distribution of the infiltrates can be unilateral or bilateral. Platelike atelectasis is noted as thin, flat areas of collapsed lung and is often seen on a lateral image of the chest. Pleural effusions develop in less than 20% of patients; when present, they can be seen on lateral decubitus films.

Reticulonodular or interstitial infiltrates, primarily in the lower lobes, may resemble other diseases with granulomatous pathology, such as tuberculosis, mycoses, and sarcoidosis; hilar adenopathy is sometimes mistaken for malignancy.

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CT Scanning

High-resolution computed tomography (CT) scans of the chest are more sensitive than chest radiography in elucidating lung disease. [22] CT findings include a tree-in-bud pattern, centrilobular nodular opacities, patchy distribution, ground glass opacities, consolidation, and pleural effusion in 15-20%.

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Sputum Culture

Sputum Gram stains and cultures are usually not helpful because M pneumoniae lacks a cell wall and cannot be stained. M pneumoniae is difficult to culture, requires special culture media, and needs 7-21 days to grow. Routine culturing is successful in only 40-90% of cases and does not provide information to guide patient management. Rapid pharyngeal culture for M pneumoniae has shown promising results. [23]

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Serology

Serum cold agglutination is a nonspecific test for M pneumoniae, but findings are positive in only 50-70% of patients after 7-10 days of infection. Cold agglutinin tests can be obtained from diagnostic laboratories. A negative result does not exclude infection, and this test may be affected by cross-reactions with other pathogens, such as adenovirus, Epstein-Barr virus, and measles viruses. A quick bedside test can be performed by partially filling a purple-top tube with blood and placing it in ice. A positive finding is one in which "grains of sand" appear on the glass portion of the tube.

Serology tests that demonstrate a 4-fold or greater increase or decrease in paired sera titers or a single titer greater than or equal to 1:32 supports the diagnosis of mycoplasmal pneumonia. Serologic tests include complement fixation, enzyme-linked immunoassay, and indirect hemagglutination. All of these have acceptable sensitivity and specificity.

Optimized serodiagnosis of M pneumoniae using a new set of antigens has shown comparable sensitivity to positive real-time polymerase chain reaction (PCR) results. [24]

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Polymerase Chain Reaction

Polymerase chain reaction (PCR) has been shown to accurately diagnose atypical pneumonia and is becoming the criterion standard confirmatory test for M pneumoniae. [25, 26] This test has been used for epidemiologic studies but is not currently used in most clinical settings. Real-time PCR is a promising test that allows detection of M pneumoniae DNA in all phases of infection, including early periods when the serum may be negative for antibody. [27, 28]

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DNA Probes

A radiolabeled DNA probe detects M pneumoniae ribosomal RNA in respiratory secretions with 90% sensitivity.

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Eosinophil Cationic Protein

The role of eosinophil cationic protein (ECP) has been studied in M pneumoniae infection and asthma, in which ECP levels have been found to be increased. [29] This protein may play a role in damage to the respiratory epithelium and accelerated hypersensitivity in the respiratory system, although more studies are required.

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