eMedicine Specialties > Emergency Medicine > Pulmonary

Pneumonia, Mycoplasma: Differential Diagnoses & Workup

Author: Michael J Bono, MD, FACEP, Professor of Emergency Medicine, Associate Director of Emergency Medicine Residency Program, Department of Emergency Medicine, Eastern Virginia Medical School
Contributor Information and Disclosures

Updated: Aug 5, 2008

Differential Diagnoses

Pediatrics, Pneumonia
Pneumonia, Aspiration
Pneumonia, Bacterial
Pneumonia, Empyema and Abscess
Pneumonia, Immunocompromised
Pneumonia, Viral

Other Problems to Be Considered

Chlamydia pneumoniae
Legionella pneumophila
Chlamydia psittaci
Chlamydia trachomatis
Coxiella burnetii (Q fever)

Workup

Laboratory Studies

  • The WBC count generally is not helpful, since results may be normal or elevated. Hemolytic anemia has been described, but it is rare.
  • Sputum Gram stains and cultures usually are not helpful, since M pneumoniae lacks a cell wall and cannot be stained. 
  • Elevated erythrocyte sedimentation rates may be present but are nonspecific.

Imaging Studies

  • Radiographic findings are variable, but abnormalities are usually more striking than the findings on physical examination. 
    • Bronchopneumonia often involves a single lower lobe. Lobar consolidation is rare.
    • Platelike atelectasis is noted as thin, flat areas of collapsed lung and often is seen on a lateral image of the chest.
    • Reticulonodular or interstitial infiltrates, primarily in the lower lobes, may resemble other diseases with granulomatous pathology, such as tuberculosis, mycoses, and sarcoidosis. 
    • Hilar adenopathy sometimes is mistaken for malignancy.
    • Pleural effusions develop in fewer than 20% of patients; when present, they can be seen on lateral decubitus films.
  • High-resolution CT scans of the chest are more sensitive than chest radiography in elucidating lung disease.

Other Tests

  • M pneumoniae is difficult to culture and requires 7-21 days to grow; culturing is successful in only 40-90% of cases and does not provide information to guide patient management.
  • 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
    • Serum cold agglutination is a nonspecific test for M pneumoniae, but findings are positive in 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, 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.
    • Other serological tests include complement fixation, enzyme-linked immunoassay, and indirect hemagglutination. All of these have acceptable sensitivity and specificity.
  • Polymerase chain reaction
    • Polymerase chain reaction (PCR) has been shown to accurately diagnose atypical pneumonia and has been used for epidemiologic studies, but it is currently not 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.
    • A radiolabeled DNA probe detects M pneumoniae ribosomal RNA in respiratory secretions with 90% sensitivity.
    • Eosinophil cationic protein (ECP) has been studied in M pneumoniae infection and asthma and may show some promise. ECP measures damage to the respiratory epithelium.

More on Pneumonia, Mycoplasma

Overview: Pneumonia, Mycoplasma
Differential Diagnoses & Workup: Pneumonia, Mycoplasma
Treatment & Medication: Pneumonia, Mycoplasma
Follow-up: Pneumonia, Mycoplasma
References
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Further Reading

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Keywords

mycoplasma pneumonia, mycoplasmal pneumonia, Mycoplasma pneumoniae, M pneumoniae, CAP, community-acquired pneumonia, atypical pneumonia, sore chest, tracheal tenderness, dry cough, bullous myringitis, pharyngeal erythema, scratchy sore throat

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Contributor Information and Disclosures

Author

Michael J Bono, MD, FACEP, Professor of Emergency Medicine, Associate Director of Emergency Medicine Residency Program, Department of Emergency Medicine, Eastern Virginia Medical School
Michael J Bono, MD, FACEP is a member of the following medical societies: Alpha Omega Alpha, American College of Emergency Physicians, American Heart Association, Medical Society of Virginia, and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.

Medical Editor

Joseph A Salomone III, MD, EMS Medical Director, Kansas City, Missouri; Associate Professor and Staff Physician, Truman Medical Centers/UMKC School of Medicine
Joseph A Salomone III, MD is a member of the following medical societies: American Academy of Emergency Medicine, National Association of EMS Physicians, and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: eMedicine Salary Employment

Managing Editor

Paul Blackburn, DO, FACOEP, FACEP, Program Director, Department of Emergency Medicine, Maricopa Medical Center; Assistant Professor, Department of Surgery, University of Arizona
Paul Blackburn, DO, FACOEP, FACEP is a member of the following medical societies: American College of Emergency Physicians, American College of Osteopathic Emergency Physicians, American Medical Association, and Arizona Medical Association
Disclosure: Nothing to disclose.

CME Editor

John D Halamka, MD, MS, Associate Professor of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center; Chief Information Officer, CareGroup Healthcare System and Harvard Medical School; Attending Physician, Division of Emergency Medicine, Beth Israel Deaconess Medical Center
John D Halamka, MD, MS is a member of the following medical societies: American College of Emergency Physicians, American Medical Informatics Association, Phi Beta Kappa, and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.

Chief Editor

Robert E O'Connor, MD, MPH, Professor and Chair, Department of Emergency Medicine, University of Virginia Health System
Robert E O'Connor, MD, MPH is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, American College of Physician Executives, American Heart Association, American Medical Association, Medical Society of Delaware, National Association of EMS Physicians, Society for Academic Emergency Medicine, and Wilderness Medical Society
Disclosure: Nothing to disclose.

 
 
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