Diagnosis of Bronchitis

Pathogenesis and Main Clinical Syndromes

The development of acute bronchitis begins with the invasion of an infectious agent into the epithelium of the lower respiratory tract. In the overwhelming majority of cases, the culprits are viruses (influenza, parainfluenza, adenovirus, coronavirus, rhinovirus, RSV). Bacteria such as Mycoplasma pneumoniae, Chlamydia pneumoniae, or the causative agent of pertussis Bordetella pertussis are much less common.

Viral aggression leads to damage to the ciliated epithelium. A local inflammatory reaction develops: the mucous membrane swells, hyperemia occurs, and the glands begin to excessively produce mucus. All of this disrupts normal mucociliary clearance. Sputum stagnates, which reflexively triggers the main symptom of the disease — cough. In some patients (especially against the background of RSV or mycoplasma infection), bronchial hyperreactivity increases, leading to bronchospasm.

The clinical presentation features three main syndromes:

• Intoxication syndrome: manifests as generalized weakness, malaise, and possible subfebrile fever (fever is not present in all patients).
• Bronchial irritation syndrome: the patient complains of discomfort or pain behind the sternum occurring during coughing. The cough itself is usually dry and agonizing in the first few days, and then becomes productive, with the release of mucous or mucopurulent sputum.
• Bronchial obstruction syndrome: occurs with marked bronchial spasm. Clinically, it is manifested by dyspnea, difficult expiration, and the appearance of wheezing.

Upon physical examination, the physician hears harsh breathing. Against this background, various rales may be detected: dry (buzzing or whistling) or moist. The most important auscultatory sign is symmetry and the absence of localized (focal) changes in the lungs.

Diagnostic Workup and Criteria for Excluding Pneumonia

Since acute bronchitis is a diagnosis of exclusion, the main task of the physician at the examination stage is to ensure that the patient does not have a more serious pathology. A syndromic approach is used for this purpose.

Mandatory diagnostic methods:

1. Thorough history-taking with evaluation of risk factors (active or passive smoking, hypothermia, hazardous occupational exposure, immunosuppression).
2. Lung auscultation.
3. Chest radiography — performed to rule out focal or infiltrative changes. It is strictly indicated if there is clinical suspicion of pneumonia or if prescribed therapy brings no relief.

Additional studies are prescribed strictly according to indications. For example, a complete blood count may be needed to detect leukocytosis, indicating a secondary bacterial infection during a protracted course. Microbiological sputum examination is relevant if the disease lasts more than three weeks, as well as when pertussis or atypical flora is suspected. Spirometry is performed in cases where the physician suspects pronounced bronchial obstruction.

An experienced clinician can use simple clinical criteria to rule out pneumonia. Pulmonary parenchymal inflammation is considered highly unlikely if all of the following conditions are met:

• body temperature does not exceed 38°C;
• heart rate is normal (no tachycardia over 100 beats per minute);
• respiratory rate does not exceed 24 breaths per minute;
• auscultation reveals no crepitus and no localized rales.

Differential diagnosis

Completely different pathologies may lurk under the mask of an ordinary cough. During differential diagnosis, the following conditions must be considered:

• Bronchiectasis. The disease presents with the production of abundant purulent sputum and frequent relapses of bacterial respiratory infections. Auscultation reveals coarse dry rales of varying pitch and moist rales of various calibers. High-resolution computed tomography (HRCT) will clearly show thickened walls and expanded bronchial lumens.
• Tuberculosis. Can begin at absolutely any age. Its confirmation requires the detection of characteristic changes on radiography and microbiological identification of the pathogen. Epidemiological history (living in a region with a high prevalence of the disease) plays an important role.
• Bronchiolitis obliterans. Most commonly starts in young, non-smoking patients. Systemic connective tissue diseases or episodes of acute toxic gas poisoning may be found in the history. The main diagnostic marker is areas of decreased lung density visualized on HRCT during the expiratory phase.
• Heart failure. In this case, the patient has a history of cardiovascular risk factors. The diagnosis is confirmed by objective signs of cardiogenic congestion in the pulmonary or systemic circulation (chest radiography, elevated filling pressures on echocardiography). Laboratory tests reveal an increase in natriuretic peptide markers (BNP and NT-proBNP). Spirometry in such patients predominantly shows a restrictive rather than an obstructive pattern.

Class and exam questions

What else to study on this topic

• Pathogenetic mechanisms of impaired mucociliary clearance during viral invasion
• Indications for antibacterial therapy in protracted cough
• Drug classes for symptomatic treatment: mucolytics, antitussives, and bronchodilators
• Spirometry features in bronchial obstruction syndrome

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.