Pneumonia and Pleurisy

WHAT IS PNEUMONIA?

Pneumonia is an inflammation of the lung, usually caused by infection. (Another term often used interchangeably with pneumonia is pneumonitis from "pneumo" meaning "of the lung" and "itis", "inflammation".) Pneumonia can also be due to causes other than infection, such as chemical irritants, radiation, aspiration of stomach contents, and so forth, In such cases the pneumonia or pneumonitis is qualified (radiation pneumonitis, chemical pneumonia, aspiration pneumonia, and so on). Unless so qualified in this chapter, "pneumonia" refers to the inflammation caused by infection.

Infection may occur in only a small part of the lung or may involve an entire lung or both lungs (so­called double pneumonia). The infecting organism grows in the lung tissue, causing the body to defend itself by mobilizing infection­fighting cells. In the process the patient develops symptoms such as chills, fever, cough, and general malaise.

These symptoms may range from very mild (often called "walking pneumonia" because the patient can walk around with it) to very severe and even fatal. Pneumonia can be caused by almost any type of organism, although a few specific viruses and bacteria are responsible for most cases, and can occur at any age.

One of the great medical advances has been the development of antibiotics for treating some of the pneumonias. Penicillin, erythromycin, and tetracycline are among the most useful. Despite this miracle group of drugs pneumonia remains a very important problem. In 1936, before the advent of antibiotics, pneumonia was the number one cause of death in the United States. Today pneumonia and influenza (a viral infection frequently complicated by pneumonia) are listed as the fifth leading cause of death.

Most pneumonia fatalities occur in elderly or debilitated patients, or in those who have compromised body defenses as may occur from chronic lung disease, cancer, or after kidney transplantation. However, pneumonia can also be fatal in young adults, particularly when due to organisms such as viruses that do not respond to antibiotics. Fortunately, most viral pneumonias are self­limiting and patients fully recover.

WHAT ARE THE INFECTIOUS CAUSES OF PNEUMONIA?

Pneumonia is caused by microscopic and submicroscopic organisms that infect the lung tissue. There are four main groups of organisms capable of causing this infection:

Bacteria: These are the relatively large organisms that can usually be seen under the microscope. They can invariably be killed or retarded with antibiotics; otherwise healthy patients who develop bacterial pneumonia respond favorably when given the appropriate antibiotic. One unusual bacterium has recently been shown to be responsible for Legionnaire's disease (discussed in a later section).

Bacteria­Like: Bacteria­like organisms fall somewhere between viruses and bacteria. They share features of both, and microbiologists do not all agree on their classification. One such organism, called mycoplasma, causes a characteristic pneumonia manifested by cough, chest pain, and a patchy infiltrate on the chest x­ray. Such lung infections are called "atypical pneumonia" to distinguish them from "typical" bacterial pneumonia. We now know that pneumonia of any particular cause can have either typical or atypical features, so the terminology is not very helpful.

Fortunately, the biochemical nature of mycoplasma and other bacteria­like organisms allows them to be destroyed or inhibited by antibiotics. Mycoplasma infections usually respond to either erythromycin or tetracycline; penicillin is ineffective.

Viruses: These are sub­microscopic organisms very different from the above two groups. They live only in cells and do not respond to antibiotics. However, the body makes a powerful anti­viral substance, interferon, that helps to control most viral infections. Viral infections are difficult to diagnose in the early stages, in part because the organisms cannot be seen with an ordinary microscope. On clinical grounds they cannot be separated from mycoplasma and other bacteria­like infections, and for this reason all patients with presumed viral pneumonia are still treated with antibiotics, usually erythromycin or tetracycline.

Miscellaneous: A large group of miscellaneous organisms may infect the lungs, including fungi, molds, parasites, and other unusual organisms that are not classified into one of the three groups above. This miscellaneous group usually infects only patients who are immuno­compromised­­whose natural immune system is depressed or compromised enough to allow unusual organisms to gain a foothold. Immune depression may occur either from an underlying disease or from treatment for the disease. Examples include kidney transplant patients who are receiving immunosuppressive agents to help prevent rejection of the kidney, cancer patients receiving drugs that depress the immune system while attacking cancer cells, and patients with blood disorders such as multiple myeloma that directly affect the body's immune system.

HOW IS PNEUMONIA DIAGNOSED?

Doctors generally go through four steps to make the diagnosis. As in any disease, the diagnosis must first be suspected before it can be made. This is not usually difficult. In fact patients will often suspect the diagnosis even before consulting a physician, because of symptoms different from any flu or cold ever experienced. High fever, chills, chest pain, and coughing up dark or foul­smelling sputum are often present in pneumonia and should always make one suspect the diagnosis. By using a stethoscope the physician can hear a "noisy" chest as air goes in and out of the inflamed passages.

In step two the physician confirms the diagnosis by chest x­ray. The chest x­ray is an invaluable test for both diagnosing and following patients with pneumonia, since it shows the extent of the disease as well as any subsequent progression or relapse. Figures 1 through 4 show some typical x­ray presentations or pneumonia.

In step three the physician attempts to find the cause. This involves ordering certain tests to help determine which organism is responsible for the infection. Such tests may include a microscopic examination of the sputum, a culture of the sputum, a count of the white blood cells (it goes up in pneumonia), and cultures of the blood to see if the pneumonia organisms have invaded the blood stream. Other tests may be ordered depending on the extent of the pneumonia, degree of symptoms, and past history of the patient.

Finally, step four is to treat with antibiotics. Rapid recovery helps to confirm the diagnosis and type of pneumonia even though the specific organism may not have been identified.

Figure 1. X-ray involving part of the right lung. The dark area is the pneumonia. Lobar pneumonia results from infection with a bacterial organism and can involve any part of either lung.

Figure 2. X­ray appearance of bilateral (double) bronchopneumonia, also due to bacterial infection.

Figure 3. Extensive broncho­pneumonia with pleural effusion.

Figure 4. Patchy viral pneumonia.

CAN TREATMENT BEGIN BEFORE THE CAUSE IS CONFIRMED?

Yes. In fact this is the rule for most pneumonias. Commonly the presence of pneumonia is confirmed (step one and two) and tests are ordered to diagnose the infecting organism (step three). The white blood cell count, rapidly obtainable, may help distinguish viral from bacterial cause since it tends to be higher when bacteria are the culprit. A sputum exam under the microscope takes only a few minutes and may give a clue as to which specific bacterium, if any, is responsible. More specific information may be obtained from culturing (growing) the organism from the sputum or a blood sample, but this takes one or more days.

Meanwhile, the patient is ill and will likely get worse waiting for culture results. For this reason, an antibiotic is begun soon after the diagnosis (but not the specific cause) is confirmed. The choice of antibiotic is based on the organism most likely responsible, as determined from the patient's history, chest X­ray appearance, sputum examination, white blood cell count, and so forth. For most pneumonias the choice of antibiotic is not medically difficult and treatment should not be delayed.

WHAT IS LOBAR PNEUMONIA?

This is pneumonia confined to one specific "lobe," or part of the lung. The lungs are normally divided into five lobes, three for the right and two for the left lung. These are clearly defined by landmarks on the chest x­ray, so lobar pneumonia is easily diagnosed. An example of lobar pneumonia is shown in Figure 1.

Lobar pneumonia is probably the most common type of pneumonia seen. It is usually caused by a specific organism, streptococcus pneumoniae, also referred to as the "pneumococcus."

Pneumococcal pneumonia is something of a paradox. The responsible organism is exquisitely sensitive to penicillin and patient response is often dramatic. Yet this same bacterium is responsible for thousands of pneumonia deaths each year in this country. The reason appears to be due to inadequate "host defenses" in many patients. For any antibiotic to work, the body must mobilize its own response to the infecting organism. This natural response is in part the increased white blood cells seen in most infections. Without this and other normal host defenses even the best antibiotics are of no use. Although penicillin is very effective in otherwise healthy people, certain patient groups have lowered defenses. They are more susceptible to severe pneumonia and more likely to show decreased antibiotic responsiveness. Such groups include very elderly patients, those with severe and chronic underlying disease (heart, lung or kidney failure), and patients with sickle cell disease, an inherited blood disorder that interferes with the body's natural response to the infecting pneumococcus.

IS THE PNEUMONIA VACCINE HELPFUL?

The pneumonia vaccine is pneumococcal vaccine, designed to prevent infection with the most virulent types of pneumococcus. There are over 70 serologic subtypes of this organism, but 14 of them account for most of the fatal cases of pneumococcal pneumonia. The vaccine contains killed strains of these 14 and is given to augment or enhance the body's natural response to infection from these pneumococcal subtypes. It is indicated mainly for the groups of patients mentioned in the [previous section] who are at increased risk and is not necessary for the general population. (See also Section K)

WHAT IS LEGIONNAIRE'S DISEASE?

In July 1976 a "new" disease made the headlines. It began with an outbreak among people attending an American Legion convention in Philadelphia. Many legionnaires staying at one particular hotel came down suddenly with a severe and fatal form of pneumonia. Despite extensive investigation and theorizing, the cause remained elusive throughout 1976. Was it due to water contamination? Air­borne virus? Poison? Would the cause ever be found? Legionnaire's Disease, as the condition is now called, was the medical enigma of 1976.

The answer came in late December, and announced in January 1977. Working at the Center for Disease Control in Atlanta, investigators discovered the culprit: a small bacterium. This unusual organism was officially named legionella pneumophila and has now been shown to be sensitive to erythromycin, an antibiotic available for many years. Erythromycin can cure Legionnaire's Disease. Had this been known in 1976, many lives might have been saved.

Even more remarkable is the fact that Legionnaire's Disease is not really new! Investigators have examined stored blood samples from previously undiagnosed outbreaks of pneumonia and found legionella pneumophila the cause in hundreds of cases – all occurring before 1976!

We now know that Legionnaire's Disease can be mild or severe. The first few days of illness may be very similar to the flu syndrome and diarrhea may be present. The x­ray appearance is extremely variable and of little help in separating Legionnaire's from other causes of pneumonia. Although it may take some time to confirm the diagnosis (depending on the test used), any patient suspected of having Legionnaire's Disease is immediately treated with erythromycin.

DO PATIENTS HAVE TO BE HOSPITALIZED WITH PNEUMONIA?

Not all pneumonia patients have to be hospitalized. The milder the symptoms and the younger the patient (excluding infants and small children), the less likely is the need for hospitalization. Generally the following groups of patients should be hospitalized:

• Anyone toxic or severely ill from pneumonia or anyone short of breath at rest.
• Anyone unable to take oral fluids or unable to receive adequate care at home.
• Any patient with a complicating illness, such as heart failure, chronic obstructive lung disease, or chronic renal disease.

WHAT IS PLEURISY?

Pleurisy refers to inflammation of the lining of the lung, the pleura (see also Section L). Pleurisy may be due to a variety of causes, most commonly a viral infection. However, any of the organisms that can cause pneumonia can also infect the pleura and lead to pleurisy. Pleurisy (another term is pleuritis) is often painful, in contrast to pneumonia which is not painful (unless the pleura are involved). This is because the lining of the lung is filled with nerve fibers that, when inflamed or stretched, cause pain. Since we normally stretch the pleura with quiet breathing, stretching of the inflamed nerve fibers is often unavoidable. It is common for patients suffering from pleurisy to take only shallow breaths, because deep breaths cause so much pain.

On the chest x­ray pleurisy may be accompanied by fluid around the lung, so­called pleural effusion (see Section L). Occasionally, bacterial infection in the pleural space can cause pus to form. This is called empyema and always has to be drained with a chest tube or by some other technique. Pleural space infected with bacteria may not have the characteristics of "pus," but still require tube drainage. Some physicians refer to any such infected fluid as an empyema or empyema­like.

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