Pneumonia

Pneumonia is an inflammation of the lungs. The term is almost always used to refer specifically to infections of the lungs caused by bacteria, viruses, fungi or other parasites; however, it can also refer to lung injury caused by physical or chemical irritants, in which case the term pneumonitis is used to differentiate the condition from infectious pneumonia. This article uses pneumonia only in the first sense, that of infection. Pneumonia may occur in people of all ages, although young children, the elderly, and immunocompromised patients are especially at risk. Antimicrobial drugs are often used to treat pneumonia.

Diagnosis

The differential diagnosis of pneumonia includes atelectasis, lung abscess, lung cancer, pulmonary embolism, and sepsis. To diagnose pneumonia, doctors rely on a patient's clinical history, findings from physical examination, and confirmatory scanning and pathology, typically including chest X-rays, blood tests, and sputum cultures. The chest X-ray is the usual standard for diagnosis in hospitals or clinics with access to X-ray facilities; however, in a community setting (general practice), doctors typically decide whether to start antibiotics for mild cases of pneumonia on the basis of a history and physical examination alone.

Related Topics:
Differential diagnosis - Atelectasis - Lung abscess - Lung cancer - Pulmonary embolism - Sepsis - Clinical history - Physical examination - General practice

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In nosocomial pneumonia (pneumonia that was acquired while the patient was in hospital for other treatment) and in immunocompromised patients, a clear diagnosis of pneumonia can be difficult; thus, a chest CT scan and/or other tests are often required to rule out causes such as pulmonary embolism). CT scanning may be useful when the symptoms and physical examination suggest several possible causes for the complaints (e.g., vasculitis, sarcoidosis, or lung cancer).

Related Topics:
CT scan - Pulmonary embolism - Vasculitis - Sarcoidosis - Lung cancer

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Physical examination

Apart from the history, the physical examination is an essential part of the doctor's overall assessment of the patient. Important features to note include whether the patient is breathless, able to speak in full sentences, uses accessory muscles of respiration, or has signs of reduced oxygenation (for example, blue, cyanotic lips, or unexplained mental confusion). If this overall assessment is poor, admission to hospital is usually advised, whatever else the examination reveals.

Related Topics:
History - Cyanotic

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The pulse rate, respiratory rate and temperature are measured. Feeling for the expansion movements of the chest wall (palpation) and tapping the chest wall (percussion) to find resonant and dull areas may provide clues to the underlying disease process affecting the patient's lungs. Finally, auscultation with a stethoscope allows the doctor to listen for any areas of the lung which have reduced air flow, crackles (crepitus or 'rhonchi') or the crunch-sound (pleural rub) of pleurisy.

Related Topics:
Pulse rate - Percussion - Resonant - Stethoscope - Crepitus - Pleural rub - Pleurisy

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Chest X-rays, sputum cultures and other tests

The history and clinical examination often indicate the likelihood of the presence of pneumonia, and what alternative conditions may need to be ruled out. Depending on the setting, the severity of a patient's condition, the reliability of the diagnosis, and local conventions of medical practice, a doctor may consider arranging for laboratory testing and/or imaging to confirm the initial clinical data. The tests may include cultures of sputum and blood, a chest X-ray, and blood tests.

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According to Harrison's Principles of Internal Medicine, "The usual standard for the diagnosis is chest radiography, which, however, is not 100% sensitive." In the proper clinical setting, an increase in opacity in one or more lung fields on a chest x-ray, indicating consolidation of the infection in that region, helps to confirm the diagnosis of pneumonia. In community settings, radiologic studies can often take up to a fortnight to be interpreted. Chest X-rays are therefore only used by doctors practising in the community to investigate patients who are failing to respond to treatment, or who have easy access to chest radiography, such as an outpatient clinic run by a hospital. This is very different from the approach taken in the emergency room of a hospital, where the X-ray film is available for immediate viewing and therefore typically forms part of the initial investigations. Chest X-rays are not always accurate, either: they may miss pneumonias that can be seen on high-resolution computed tomography scans; they will miss pneumonias in which radiological signs have not yet developed, and they may result in the misdiagnosis of pneumonia when some other condition, such as pulmonary fibrosis or congestive heart failure, is responsible for the radiographic opacity. Opacities in the lower lobes are difficult to differentiate from atelectasis.

Related Topics:
Harrison's Principles of Internal Medicine - Chest x-ray - Radiologic - Emergency room - High-resolution computed tomography - Pulmonary fibrosis - Congestive heart failure - Atelectasis

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Should a doctor have any specific concerns about the diagnosis, or should a patient fail to recover after a course of antibiotics, a culture of the patient's sputum is normally requested. However, because it generally takes at least two days for a full analysis, sputum cultures are usually used only to retrospectively confirm the sensitivity of an infection to the antibiotic that has already been started. If possible, the culture should be collected prior to the start of antibiotics. The possibility of tuberculosis should be considered when a cough has been present for several weeks, or fails to respond to standard antibiotics. Special testing for tuberculosis needs to be specifically requested of the laboratory, because the bacterium that causes tuberculosis (Mycobacterium tuberculosis) cannot identified through the normal culturing process.

Related Topics:
Culture - Sputum - Tuberculosis - Mycobacterium tuberculosis

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In the inpatient hospital setting, a blood sample is often routinely cultured to detect infection in the bloodstream (blood culture). As with sputum cultures, if the cultures grow bacteria, they can be identified and then tested to see which antibiotics will be most effective. Antimicrobial therapy can then be switched accordingly.

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Supportive diagnostic tests usually include a full blood count; this may show a raised white cell count (neutrophilia), indicating the presence of an infection or inflammation (however, in some immunocompromised patients, the white cell count may appear deceptively normal). Renal function may have deteriorated if there is sepsis. There may be hyponatremia (low sodium levels), often due to the secretion of antidiuretic hormone by lung tissue; this is thought to be more frequent in tuberculosis and Legionaires' disease. Specific serological assays for atypical pathogens (Mycoplasma, Legionella and Chlamydophila) are also available.

Related Topics:
Full blood count - Neutrophilia - Immunocompromise - Renal function - Sepsis - Hyponatremia - Antidiuretic hormone - Tuberculosis - Legionaires' disease - Serological

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In addition, there is now available a urine test for Legionella antigen.

Related Topics:
Urine - Antigen

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