A 63-year-old man comes to the office due to 3 months of increasing cough with occasional hemoptysis, night sweats, and unintentional weight loss. The patient recently emigrated from South Africa, where he had worked for many years in the gold mines. He has a history of silicosis that was diagnosed 10 years ago. Vital signs show a low-grade fever. Physical examination reveals diffuse, fine crackles with right upper lobe predominance. Chest x-ray shows diffuse, small nodules; hilar adenopathy with prominent calcifications; and a cavitary lung lesion in the right upper lobe. A sputum sample is sent for appropriate staining and culture. This patient's increased susceptibility to the current infection is best explained by which of the following factors?

Question

A 63-year-old man comes to the office due to 3 months of increasing cough with occasional hemoptysis, night sweats, and unintentional weight loss.  The patient recently emigrated from South Africa, where he had worked for many years in the gold mines.  He has a history of silicosis that was diagnosed 10 years ago.  Vital signs show a low-grade fever.  Physical examination reveals diffuse, fine crackles with right upper lobe predominance.  Chest x-ray shows diffuse, small nodules; hilar adenopathy with prominent calcifications; and a cavitary lung lesion in the right upper lobe.  A sputum sample is sent for appropriate staining and culture.  This patient's increased susceptibility to the current infection is best explained by which of the following factors?

Quizplus · Accepted Answer

This patient with a history of silicosis has developed hemoptysis, night sweats, weight loss, and a cavitary lung lesion in the upper lobe; this is highly suggestive of tuberculosis infection. Silicosis is an occupational lung disease that occurs after inhalation of crystalline silica and is characterized by multiple rounded nodules located in the upper lobes. Patients may also develop calcification of the rim of hilar lymph nodes (eggshell calcification). Silicosis is associated with increased risk of mycobacterial infections, particularly Mycobacterium tuberculosis, due to impaired macrophage function. It is thought that macrophage phagolysosomes are disrupted by internalized silica particles, leading to impaired phagocytosis and increased apoptosis. (Choice A) Although interstitial fibrosis can be caused by silicosis, fibrosis alone would not greatly predispose to mycobacterial infection. In fact, scarred areas of lung would be less accessible and may limit spread of microbial pathogens. (Choices B and D) Th2 cells are important for mediating humoral immunity and combating parasitic infections. However, humoral immunity does not play a major role in eliminating mycobacterial infections due to the intracellular survivability of these pathogens. (Choice E) Impaired mucociliary clearance, which occurs in patients with cystic fibrosis, can result in recurrent pulmonary infections due to impaired pathogen clearance. However, mucociliary clearance is not directly impaired by silicosis. Educational objective: In silicosis, internalized silica particles impair macrophage function by disrupting phagocytosis and promoting apoptosis. This increases the risk of mycobacteria infection (particularly M tuberculosis). __________ References: Silicosis. (http://www.ncbi.nlm.nih.gov/pubmed/22534002)

A 63-Year-Old Man Comes to the Office Due to 3