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Pneumonia

Definition: pulmonary inflammation
German: Lungenentzündung

1 Definition

A pneumonia is defined as the inflammation of the tissue of the lung. Possible causes for pneumonia are bacteria, viruses, fungi, aspiration of gastric juice, parasites, toxins (eg. by inhaling caustic gases), and other factors.

2 Classification

2.1 ...according to pathological aspects

According to clinical-pathological aspects, pneumonias are classified as

2.1.1 Alveolar pneumonia

In alveolar pneumonia, the inflammation takes place within the alveolar cells. You can further divide it into two subtypes:

  • Bronchial pneumonia: Bronchial pneumonia is a multifocal pneumonia where the inflammation of different foci of bronchial tube infections spread to the tissue of the lung. The inflammation can affect one or several pulmonary lobules, and mostly occurs in multiple pulmonary lobes at a time. A bronchial pneumonia can develop by endobronchial, peribronchial or hematogenic spread.
  • Lobar pneumonia: An entire pulmonary lobe is affected by the inflammation. This form is characterized by a disease progress in typical stages, and, as opposed to a bronchial pneumonia, it's fixed to a certain area. You can further differentiate it according to the site of infection:
    • Inferior lobar pneumonia
    • Intermediate lobar pneumonia
    • Superior lobar pneumonia

2.1.2 Interstitial pneumonia

Interstitial pneumonia does not affect the alveoles, but the interstitium, i.e. the thin layer of connective tissue between the alveoles and the blood vessels. The causes - as far as they can be identified - can vary. Among others, you need to consider infections and inhalation toxicants (eg. cigarette smoke).

Infection-caused interstitial pneumonia mostly develops by the pathogen being ingested by the alveolar macrophages and carried off to the supporting tissue.

Interstitial pneumonia can be further divided according to their disease progress:

An interstitial pneumonia whose causes are unknown is called idiopathic interstitial pneumonia (IIP). It also comprises, among others, the desquamative interstitial pneumonia (DIP) being found in smokers, and the lymphoid interstitial pneumonia (LIP).

2.2 ...according to etiology

As per the place of contagion, respectively the occurrence, of the pneumonia, you can differentiate between

  • community-acquired pneumonia (CAP): acquired outside of medical institutions
  • healthcare-associated pneumonia (HAP): Disease caused by microorganisms which is associated by chronological connection with a stay in a medical institution (eg. a hospital)
    • Pneumonia acquired in a hospital is also called "hospital-acquired pneumonia"
    • Another subgroup is the "ventilator associated pneumonia" (VAP)

2.3 ...according to surrounding circumstances

According to the circumstances surrounding its occurrence, pneumonia is divided into

2.4 ...according to clinical progression

  • typical pneumonia (= alveolar pneumonia)
  • atypical pneumonia (= interstitial pneumonia)

3 Predisposition

Factors that favor the development of pneumonia are cigarette smoking, aspiration, condition after splenectomy, age above 60 years, age below 1 year, pre-existing viral infections of the airways (bronchitis), and treatment with immunosuppressants.

4 Pathogens

The knowledge of the spectrum of pathogens causing pneumonia is important to the attending physician, since in the course of pneumonia therapy, the induction of a calculated antibiotic treatment before final pathogen diagnosis might become necessary.

The various forms of pneumonia differ regarding their pathogenic agents, which are stated in summary below.

4.1 Community-acquired pneumonia

Frequent pathogens of community-acquired pneumonia are:

4.2 Healthcare-associated pneumonia

In community-acquired forms of alveolar pneumonia, streptococcus pneumoniae is by far the most common pathogen. Mycoplasma pneumoniae is the most common pathogen in community-acquired interstitial pneumonia.

In healthcare-associated pneumonia, knowledge of the spectrum of pathogens prevailing in the respective hospital is useful.

In newborns, chlamydia trachomatis serotypes D-K and B-streptococci (eg. streptococcus agalactiae) are common pathogenic agents of pneumonia. Children are frequently affected by Respiratory Syncitial Virus. In children and adolescents, pneumonia caused by mycoplasma pneumoniae and haemophilus influenzae are relatively common compared to other age groups.

In patients on artificial ventilation, gramnegative rod-shaped bacteria such as pseudomonas aeroginosa are frequently causes of pneumonia.

In aspiration pneumonia, anaerobic bacteria often contribute to the cause.

5 Clinical presentation

The inflammatory exsudate that collects in the alveoles leads to a limitated lung function with resulting shortness of breath. The respiratory rate increases, the patient suffers from fever and cough. In alveolar pneumonia, the cough is usually productive. In contrast to that, a dry cough is characteristic for interstitial pneumonia.

During auscultation, you typically can hear wet rales. In lobar pneumonia, during auscultation, you can hear the characteristic bronchial respiration. During percussion, the resonance over the affected lobe is notably reduced. Whereas, the vocal fremitus and bronchphony are amplified.

When, in addition to that, the pleura is inflamed, too (pleuritis), the patient suffers from pain changing in intensity depending on the position of respiration. Typically, the patient takes a relieving posture, with the body inclined to the affected side and shallow breathing.

If the pneumonia is not showing the typical symptoms of pneumonia in auscultation and percussion, you call it an atypical pneumonia.

6 Diagnostics

Alongside taking the medical history and a physical exam, you have a variety of methods available for diagnostics.

For the isolation and identification of the pathogen, you can take sputum, blood cultures, pleural punctates, bronchial secretions and serological exams from the blood and urine. In complex cases, taking a biopsy sample might become necessary.

An X-ray of the chest can bring clarity regarding existing opacities, coin lesions and atelectasis.

Laboratory medicine exams contribute to securing the diagnosis.

The severity of a community-acquired pneumonia can be estimated using the CRB-65-index.

6.1 DD: typical versus atypical pneumonia

alveolar (bacterial) pneumonia

interstitial (viral) pneumonia

acute onset subacute onset
previously healthyprior history of cold disease
fever > 38,5°C, chillsfever < 38,5°C, slowly increasing
leucocytosis with left shift, CRP and ESR increaselymphocytosis, CRP and ESR within reference range
productive coughdry cough
lobular and/or lobar infiltrations in chest X-ray, particularly in the basal regioninterstitial and/or lobular infiltrations, flat frosted glass-like opacity
frequently with pleuritisrarely with pleuritis
rales, in lobar affliction additionally resonance reductionvery discrete rales, or unsuspicious in auscultation
sensation of being severely ill, tachypnea, tachycardiaweaker sensation of being ill

6.2 Diagnostic clues

Circumstances to be investigated when taking the clinical history can direct suspicion to a certain pathogen:

7 Therapy

General therapeutic measures against pneumonia are:

For the therapy of pneumonia caused by bacteria, it's advisable to use antibiotics. For that, it is important to induce broad-spectrum calculated chemotherapy with the potentially most effective antibiotics on the basis of the pathogen to be expected. In cases of lack of improvement of the patientís condition, therapy can be changed. Upon detection of the pathogen, you can go back to an antibiotic with a smaller efficacy spectrum, if possible.

In (1) and (2), you can find sources with further information on the therapy of bacterial pneumonia in general, and on healthcare-associated pneumonia in particular (in German).

Viral pneumonia cannot be treated sufficiently with the existing virostatics. Therefore, therapy comprises symptomatic treatment of the inflammation alongside the general measures.

The use of antibiotics in viral pneumonia is reasonable for the treatment or prevention of a bacterial superinfection. However, you can take a wait-and-see approach in purely viral forms under control of laboratory inflammation parameters (blood cell count, ESR, CRP).

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