Pulmonary Alterations and Infectious Diseases

1. Consolidation
2. Red hepatization
3. Gray hepatization
4. Resolution

Viral Pneumonia and Influenza

Viral pneumonia, most commonly caused by Influenza, is often seasonal and tends to be self-limiting. However, it poses a significant risk for secondary complications. The virus can damage the ciliated epithelial cells that normally serve as a defense mechanism to sweep pathogens out of the airways. This damage provides an ideal environment for secondary bacterial infections to take hold. Common clinical manifestations include fever, chills, cough, dyspnea, and pleuritic chest pain.

Exam Tip: If a patient presents with a viral illness followed by a sudden worsening of symptoms and productive cough, suspect a secondary bacterial infection due to damaged mucociliary clearance.

Tuberculosis (TB)

Tuberculosis is caused by the acid-fast bacillus Mycobacterium tuberculosis. It is transmitted via airborne droplets and remains a leading cause of death from a curable infectious disease globally.

Pathophysiology: Granulomas and Necrosis

The body attempts to isolate the bacteria by forming granulomatous lesions, also known as tubercles. Within these lesions, a specific type of cell death called caseous necrosis occurs, resulting in a "cheeselike" material.

TB can exist in two states:

• Latent TB: The infection is contained within the tubercles; the patient is asymptomatic and not contagious.
• Active TB: The bacteria multiply, causing disease and symptoms such as fatigue, weight loss, night sweats, and a purulent cough.

Diagnosis

Diagnosis involves several methods, including sputum cultures, immunoassays, and chest radiographs. The tuberculin skin test (TST), or PPD, is frequently used; however, it is important to note that a positive TST cannot distinguish between a latent infection and active disease.

Abscess Formation and Cavitation

A lung abscess is a circumscribed area of suppuration (pus formation) and destruction of the lung parenchyma. This condition typically follows a period of consolidation, where the inflammation causes the alveoli to fill with fluid, pus, and microorganisms.

As the consolidated tissue undergoes necrosis, the abscess may empty into the bronchus. This process of emptying and the subsequent formation of a hole in the lung tissue is known as cavitation. The most common cause of abscess formation is aspiration. Patients often present with fever, chills, and the production of copious, often foul-smelling sputum.

Acute Bronchitis

Acute bronchitis is an acute inflammation of the bronchi, often occurring as a follow-up to a viral illness. While it shares several symptoms with pneumonia—such as cough and fever—it is clinically distinguished by the absence of pulmonary consolidation and chest infiltrates on imaging. The cough in acute bronchitis is often nonproductive and may occur in paroxysms (sudden outbursts), frequently aggravated by cold, dry, or dusty air.

Summary Table: Differential Diagnosis