Pneumonia

Description

Alternative Names

Diagnosis

Diagnostic Difficulties in Community-Acquired Pneumonia (CAP). It is important to determine if the cause of CAP is a bacteria, atypical bacteria, or virus, since they require different treatments. In children, for example, S. pneumonia is the most common cause, but respiratory syncytial virus is also an important cause of pneumonia. Although symptoms may differ among these types, they often overlap and it is often impossible to identify the organism by symptoms alone. Nevertheless, in many cases of mild-to-moderate community-acquired pneumonia, the physician is able to diagnose and treat pneumonia based solely on a history and physical examination.

Diagnostic Difficulties in Hospital-Acquired Pneumonia (Nosocomial Pneumonia). Diagnosing pneumonia is particularly difficult in hospitalized patients (called nosocomial pneumonia) for a number of reasons, including the following:

• Many hospitalized patients have similar symptoms, including fever or signs of lung infiltration on x-rays.
• In hospitalized patients, sputum or blood tests often indicate the presence of bacteria or other organisms, but such agents do not necessarily indicate pneumonia.
• For a diagnosis of nosocomial pneumonia, physicians should be sure to rule out other conditions, using a chest x-ray, two sets of blood cultures, a urine analysis for Legionella, lung fluid sample, and possibly other tests for specific organisms.

Medical and Personal History

The patient's history is an important part of the diagnosis of pneumonia. The patient should be sure to report any of the following:

• Recent or chronic respiratory infection
• Exposure to people with pneumonia or other respiratory illnesses (such as tuberculosis)
• History of smoking
• Alcohol or drug abuse
• Recent travel
• Occupational risks

Physical Examination

Use of the Stethoscope. The most important diagnostic tool for pneumonia is the stethoscope. Sounds in the chest that may indicate pneumonia are the following:

• Rales (a bubbling or crackling sound). Rales on one side of the chest and rales heard while the patient is lying down are strongly suggestive of pneumonia.
• Rhonchi (abnormal rumblings indicating the presence of thick fluid).
• Percussion. The physician will also use a test called percussion, in which he or she taps the chest lightly. A dull thud instead of a healthy hollow-drum-like sound, indicates certain conditions that suggest pneumonia, including the following:
• Consolidation (a condition, in which the lung becomes firm and inelastic).
• Pleural effusion (fluid build-up in the space between the lungs and the lining around it).

Laboratory Tests for Diagnosing Infection and Identifying Bacterial Agents

Although antibiotics are available that can destroy a wide spectrum of organisms, it would be preferable to use an antibiotic that can target the specific microorganism causing the pneumonia. Researchers, then, are looking for laboratory tests that would identify the specific organism or virus causing the pneumonia. Unfortunately, people harbor many bacteria, and sputum and blood tests are not always effective in distinguishing between harmless and harmful microscopic agents.

In severe cases, physicians particularly need to use invasive diagnostic measures to identify the infecting agent.

Sputum Tests. A sputum sample coughed from the lungs will yield physical information that will help the physician determine severity. In addition, only a sputum sample will reveal the infecting organism.

Typically, The physician first asks the patient to cough as deeply as possible to produce an adequate sputum sample. (A shallow cough produces a sample that usually only contains normal mouth bacteria.) A person who is not able to cough sufficiently may be asked to inhale a saline spray that helps produce an adequate sputum sample. In some cases, a tube will be inserted through the nose down into the lower respiratory tract to induce a deeper cough.

The physician will check the sputum for the following indications:

• Presence of blood (an indication of infection).
• Color and consistency. If the sputum is opaque and colored yellow, green, or brown, then infection is likely. Clear, white, glistening sputum indicates no infection.

If a good sputum sample is available, it is sent to the laboratory for analysis. In the laboratory, the sample may be used as follows:

• A Gram stain is made, which may reveal the presence of bacteria and whether they are gram-negative or positive.
• A sputum culture may be performed, in which organisms are grown in the laboratory.

Blood Tests. Blood tests may be used for the following:

• White blood cell count. High levels indicate infection.
• Blood cultures. They may be performed for detecting the specific organism causing the pneumonia, but are not often helpful in distinguishing harmful from harmless organisms. They are accurate in only 10% to 30% of cases, and their use should generally be limited to severe cases.
• Detection of antibodies to S. pneumoniae. Researchers are using specialized techniques to detect antibodies to S. pneumoniae (immune factors that target specific foreign invaders), but it is not clear if they are accurate.
• Polymerase Chain Reaction. In some difficult cases, a polymerase chain reaction (PCR) may be performed. A PCR is able to make multiple copies of the genetic material (the RNA) of a virus or bacteria to the point where it is detectable.

Urine Tests. A urine test (NOW) can detect S. pneumonia within 15 minutes. It may identify up to 77% of pneumonia cases and may rule out the infection in 98% of patients who do not have S. pneumonia. It may not be very useful in diagnosing S. pneumoniae as a cause of pneumonia in children, since the organism is so common anyway in this population, whether they have pneumonia or not.

Laboratory Tests for Less Common Organisms

If uncommon organisms, such as Legionella, Mycoplasma, and Chlamydia organisms, are strongly suspected more advanced laboratory tests may be used:

• Specialized techniques can detect antibodies to the organisms in blood samples, but these antibodies, such as those responding to Mycoplasma or Chlamydia, are not present early enough in the course of pneumonia to permit prompt diagnosis and treatment.
• A test performed on whole blood samples that uses a technique called polymerase chain reaction (PCR) is useful for identifying certain atypical strains, including Mycoplasma and Chlamydiapneumoniae and possibly Haemophilus influenzae type b, but it is expensive.
• A urine test can be used to diagnose some cases of Legionnaire's disease.
• Specialized tests called DNA probes are being developed to detect these organisms in respiratory secretions.
• In addition, special stains and cultures are required to detect fungal infections.

Chest X-Rays and Other Imaging Techniques

X-Rays. A chest x-ray is nearly always taken to confirm a diagnosis of pneumonia. It may reveal the following:

• White areas in the lung called infiltrates, which indicate infection.
• Complications of pneumonia, including pleural effusions (fluid around the lungs) and abscesses.

Other Imaging Tests. Computed tomography (CT) scans or magnetic resonance imaging (MRI) scans may be useful in some circumstances, such as the following:

• If x-ray results are unclear.
• When patients do not respond to antibiotics.
• When patients have complications.
• When patients have other serious health problems.

These more sophisticated imaging techniques can help detect the presence of tissue damage, abscesses, and enlarged lymph nodes. They can also detect some tumors that block bronchial tubes. No imaging technique can determine the actual organism causing the infection.

Invasive Diagnostic Procedures

Invasive diagnostic procedures may be required in the following circumstances:

• When patients have life-threatening complications.
• When patients have failed standard treatments for no known reason.
• When AIDS or other immune problems are present.

Each of the procedures has potentially serious complications and is not used under ordinary conditions to diagnose pneumonia.

Thoracentesis. If a doctor detects pleural effusion on either the physical exam or on imaging studies and suspects that empyema (pus) is present, thoracentesis is performed:

• Fluid in the pleura is withdrawn using a long thin needle inserted between the ribs.
• The fluid is then sent to the lab for multiple tests.

Complications of this procedure are rare, but include collapsed lung, bleeding, and introduction of infection.

Bronchoscopy. A bronchoscopy employs the following:

• The patient is given a local anesthetic, supplementary oxygen, and sedatives.
• The physician inserts a fiberoptic tube into the lower respiratory tract through the nose or mouth.
• The tube acts like a telescope into the body, allowing the physician to view the windpipe and major airways for pus, abnormal mucus, or other problems.
• The doctor removes specimens for analysis and can also treat the patient by removing any foreign bodies or infected tissue encountered during the process.

Bronchoalveolar lavage (BAL) may be employed with bronchoscopy. This involves injecting high amounts of saline through the bronchoscope into the lung and then immediately suctioning the fluid back, which is then analyzed in the laboratory. Studies find BAL to be an effective method for detecting specific infection-causing organisms.

The procedure is usually very safe, but complications can occur. They include allergic reactions to the sedatives or anesthetics, asthma attacks in susceptible patients, and bleeding. Fever may follow the procedure.

Lung Biopsy. In very severe cases of pneumonia or when the diagnosis is unclear, particularly in patients with damaged immune systems, a lung biopsy may be required. Biopsies can be performed in one of two ways:

A Lung Tap. This procedure typically uses a needle inserted between the ribs to draw fluid out of the lung for analysis. It is known by a number of names including lung aspiration, lung puncture, thoracic puncture, transthoracic needle aspiration, percutaneous needle aspiration, and needle aspiration. It is a very old procedure that is not done often any more, particularly in children, since it is invasive and poses a slight risk for collapsed lung. Some experts argue, however, that a lung tap offers a more accurate solution than other methods for identifying bacteria and the risk it poses is slight. Given the increase in resistant bacteria, they believe its use should be reappraised in young people.

Ruling Out Other Disorders that Cause Coughing or the Affect the Lung

Common Causes of Persistent Coughing. Over 30 million people seek medical help each year for persistent coughing, which is nearly always temporary and harmless when other symptoms, such as fever, are not present. Roughly, the first four most common causes of persistent coughing are asthma, postnasal drip, gastroesophageal reflux disease (GERD, a cause of heartburn), and chronic bronchitis. Other obvious common causes of chronic cough include heavy smoking or the use of heart drugs known as ACE inhibitors.

Acute Bronchitis. Acute bronchitis is an infection in the passages that carry air from the throat to the lung causing a cough that produces phlegm. It is almost always caused by a virus and usually resolves on its own within a few days. (In some cases, acute bronchitis caused by a cold can last for several weeks, and some physicians believe that a cough should not be considered to be chronic until it persists for eight weeks.)

Chronic Bronchitis. Chronic bronchitis causes shortness of breath and is often accompanied by infection, mucus production, and coughing, but it is a long-term and irreversible condition. The same microbes that cause pneumonia can cause chronic bronchitis, and symptoms of the two disorders are often similar. They include fatigue, coughing, fever, and production of sputum. There are significant differences between chronic bronchitis and pneumonia:

• Patients with bronchitis are less likely to have wheezing, shortness of breath, chills, very high fevers, and other signs of severe illness.
• Those with pneumonia usually cough up heavy sputum, which is also more likely to contain blood.
• X-rays of patients with bronchitis are unlikely to show fluid or consolidation in the lung.

Asthma. In asthma, the cough is accompanied by wheezing and occurs mostly at night or during activity. Fever is rarely present (unless the patient also has an infection). Asthmatic symptoms from occupational causes can cause persistent coughing, which is usually worse during the work week. Tests called the methacholine inhalation challenge and pulmonary function studies may be effective in diagnosing asthma.

Anthrax. Because of current terrorist concerns, it is important to differentiate between anthrax and community-acquired pneumonia. According to one study, people with inhalation anthrax are more likely to have rapid heart rate and less likely to have headache, nasal symptoms, and muscle aches than those with pneumonia. Laboratory studies with anthrax also show high hematocrit and low albumin and sodium levels. Certain chest x-ray findings also raise the likelihood of anthrax.

Other Disorders that Affect the Lung. Many conditions mimic pneumonia, particularly in hospitalized patients. Some include the following:

• Tuberculosis.
• Bronchial asthma.
• Bronchiectasis (irreversible widening of the airways, usually associated with birth defects, chronic sinus or bronchial infection, or blockage).
• Atelectasis (collapse of lung tissue).
• Heart failure. (If heart failure affects the left side of the heart, fluid-build up can occur in the lungs and cause persistent cough, shortness of breath, and wheezing. In such cases, symptoms are usually worse at night.)
• Severe allergic reactions, such as to drugs.
• Adult respiratory distress syndrome (ARDS).
• Lung cancer.
• Interstitial pulmonary fibrosis (a non-infectious inflammation of the lung is marked by progressive damage and scarring). It can occur from a number of conditions, including chemicals, injury, autoimmune disease, and cancer. The cause is often unknown.

Ruling Out Causes in Children. Important causes of coughing in children at different ages include:

• Asthma.
• Physical abnormalities in infants under 18 months.
• Sinusitis in children 18 months to six years.
• Psychologic causes in older children and adolescents.