A 54-year-old man comes to the emergency department due to fevers, shaking chills, and cough productive of copious sputum. He began having fever, cough, and sharp chest pains 10 days ago and was prescribed oral antibiotics by his primary care physician after a chest x-ray revealed a right lower lobe infiltrate. The patient has not been taking the medication as advised, and his symptoms have progressively worsened. Temperature is 39 C (102.2 F), blood pressure is 114/62 mm Hg, and pulse is 116/min. Physical examination reveals crackles in the right lower lung. Repeat chest x-ray reveals a round density with an air-fluid level in the lower lobe of the right lung. Which of the following is the most important contributor to the observed lung lesion in this patient?

Question

A 54-year-old man comes to the emergency department due to fevers, shaking chills, and cough productive of copious sputum.  He began having fever, cough, and sharp chest pains 10 days ago and was prescribed oral antibiotics by his primary care physician after a chest x-ray revealed a right lower lobe infiltrate.  The patient has not been taking the medication as advised, and his symptoms have progressively worsened.  Temperature is 39 C (102.2 F), blood pressure is 114/62 mm Hg, and pulse is 116/min.  Physical examination reveals crackles in the right lower lung.  Repeat chest x-ray reveals a round density with an air-fluid level in the lower lobe of the right lung.  Which of the following is the most important contributor to the observed lung lesion in this patient?

Quizplus · Accepted Answer

Lung abscess is a necrotic infection of the pulmonary parenchyma that usually presents with several days of fever, cough productive of copious sputum (often foul-smelling), and chest x-ray evidence of cavitation with air-fluid level. Most cases are due to aspiration of anaerobic bacteria from the oropharynx, but lung abscess can also develop in the setting of untreated pneumonia. Neutrophils are the key player in the formation of lung abscess. They are recruited from the systemic circulation by chemokines and are subsequently activated by microbial molecules (eg, lipopolysaccharide, peptidoglycan, bacterial DNA) and opsonizing factors (eg, IgG, complement) to phagocytize and destroy the pathogenic bacteria. Activated neutrophils also release cytotoxic granules (lysosomes) containing myeloperoxidase and other digestive enzymes that destroy extracellular bacteria and recruit additional immune components to the area. However, these enzymes also cause significant damage to the pulmonary parenchyma and can result in liquefying necrosis of lung tissue and (potentially) lung abscess. (Choices A and B) Dendritic and other antigen-presenting cells release interleukin-12, which stimulates differentiation of Th1 helper cells and production of interferon-gamma by T-cells. Interferon-gamma activates macrophages, leading to the development of mature phagolysosomes capable of destroying phagocytosed bacteria. Macrophages are particularly important for the elimination of certain intracellular infections such as Mycobacterium tuberculosis. Although tuberculosis can be associated with pulmonary cavitation, the cavitations usually form in the upper lobes and generally take months to develop. (Choice D) Major basic protein is the predominant component of eosinophilic granules and plays a crucial role in the elimination of parasites. Lung abscess formation is primarily mediated by neutrophils, not eosinophils. (Choice E) Transforming growth factor-beta is secreted by inflammatory cells and results in the recruitment of fibroblasts and the deposition of connective tissue. This cytokine contributes to scar formation after injury and plays a role in the fibrosis seen with chronic inflammation. Educational objective: Abscess formation is largely driven by neutrophil recruitment and activation leading to the release of cytotoxic granules that kill bacteria but also cause liquefying necrosis of surrounding tissue. __________ References: The multifaceted function of neutrophils. (http://www.ncbi.nlm.nih.gov/pubmed/24050624)

A 54-Year-Old Man Comes to the Emergency Department Due to Fevers