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Differential diagnosis of lung diseases

The basis of the differential diagnosis of lung diseases is the search for localized inflammatory changes. The presence of an inflammatory focus confirms pneumonia and helps differentiate it from ARVI, acute bronchitis, and bronchiolitis.

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PneumoniaThe key marker is localized physical and radiological changes.
ARVIAbsence of focal lesions, intoxication, and catarrhal symptoms.
Acute bronchitisScattered rales that change after coughing; hyperresonant (tympanic) percussion sound.
BronchiolitisSevere respiratory failure in children under 1 year of age without localized foci.
2 min readFor medical studentsUpdated 10.10.2026
Material prepared by WhiteCoat Pro editorial team based on platform study guidesPending instructor review

Principles of differential search

Differential diagnosis is based on excluding pathologies with similar respiratory symptoms but without localized changes in the lungs.

Acute bronchitis

  • Presents with moderate fever and a cough that transitions from dry to productive.
  • Dyspnea is usually absent.
  • Auscultation reveals harsh breath sounds and scattered moist rales that change character or disappear after the child coughs.
  • The percussion sound acquires a hyperresonant (box-like) tint.
  • Radiography shows diffuse changes: enhanced bronchovascular markings and decreased clarity of the root structures, without foci.

Acute respiratory viral infection (ARVI)

  • Intoxication and catarrhal symptoms come to the forefront.
  • The temperature may be high but usually subsides within the first 3 days.
  • The main difference is that there are no localized changes in the lungs upon percussion, auscultation, or imaging.

Features of bronchiolitis

Bronchiolitis most commonly affects infants in their first year of life.

  • In terms of intoxication severity, it closely resembles pneumonia.
  • Severe respiratory failure develops rapidly: marked dyspnea with involvement of accessory muscles, and cyanosis around the mouth or generalized.
  • Cor pulmonale (cor pulmonale) rapidly develops.
  • Percussion reveals a hyperresonant sound (sign of emphysema), while auscultation reveals diminished breath sounds and numerous scattered fine bubbling rales.
  • Despite the severe clinical picture, there are no localized infiltrative foci on the radiograph.
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Confirming pneumonia

To reliably diagnose pneumonia, it is necessary to find localized physical changes. For example, dullness on percussion and localized diminution of breath sounds in a specific area.

According to WHO, the "gold standard" of diagnostics is chest radiography. Detecting infiltrative changes on the image confirms the diagnosis and also reveals the nature and precise localization of the inflammation.

Indications for hospitalization

Pneumonia can be treated at home (as a "hospital at home" with daily monitoring), but in a number of cases, hospitalization is mandatory:

  • Age of the child under 1 year.
  • Severe or complicated course of the disease.
  • Burdened somatic status or poor premorbid background.
  • Inability to provide proper care and treatment at home.

Patients are referred to pulmonology departments. Wards are filled simultaneously (cyclical admission principle) to prevent cross-infection.

How to memorize

Pneumonia = Spot (focal shadow on imaging) + Dullness (localized). Bronchitis = Storm (diffuse rales everywhere).

Class and exam questions

What is the main difference between pneumonia and bronchitis?

In pneumonia, changes (rales, percussion dullness, focus on X-ray) are localized in a specific area. In bronchitis, changes are diffuse and scattered, and rales change after coughing.

How to distinguish bronchiolitis from pneumonia in an infant?

Bronchiolitis causes severe respiratory failure and an abundance of fine bubbling rales throughout the lungs against the background of a hyperresonant sound, but on X-ray, unlike pneumonia, there will be no infiltrative foci.

Does peak flowmetry serve as a diagnostic tool for lung foci?

No, peak flowmetry is used only for monitoring external respiration function (assessing peak expiratory flow).

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