A 58-year-old man comes to the emergency department due to a week of fever, chills, and cough productive of foul-smelling sputum. He has also had night sweats, anorexia, and fatigue. The patient has no other medical conditions and takes no medications. He has unstable housing and often sleeps in doorways or at shelters. The patient smokes cigarettes and drinks alcohol but does not use injection drugs. Temperature is 39.5 C (103.1 F), blood pressure is 110/70 mm Hg, and pulse is 120/min. The patient appears ill and disheveled with poor dentition. Lung auscultation reveals right-sided crackles. Leukocyte count is 18,000/mm³, and serum sodium is 128 mEq/L. Chest imaging findings are shown in the image below: Which of the following is the most likely cause of this patient's current condition?

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11ec25c8_d88b_7dfa_bc81_adc1d13a078b_MD0003_00 This patient's alcohol use, foul-smelling sputum, fever, leukocytosis, and cavitary infiltrate with air-fluid level likely indicates lung abscess. Most cases are caused by the aspiration of oropharyngeal anaerobic bacteria (eg, Peptostreptococcus, Fusobacterium) in the setting of dysphagia or impaired consciousness (eg, due to alcohol abuse or seizures). Those with poor dentition or gingival disease are at greatest risk. Because anaerobic bacteria grow slowly, manifestations generally arise over 1-2 weeks. Common symptoms include fever, night sweats, weight loss, and cough with foul-smelling sputum. Although the mechanism is unclear, pulmonary infections (eg, pneumonia, lung abscess) and malignancies often cause mild hyponatremia due to the syndrome of inappropriate antidiuretic hormone secretion (SIADH). Chest x-ray and CT scan typically reveal cavitary infiltrates, often with air-fluid levels in the superior lower lobe or posterior upper lobe (sections that are dependent with recumbency). cavitary infiltrates Anaerobic bacteria are difficult to isolate on culture. Therefore, patients with suspicious symptoms generally receive empiric antibiotics with an agent that has good pulmonary penetration and efficacy against obligate and facultative anaerobes. Ampicillin-sulbactam is considered first-line therapy. Clindamycin is reserved for those with beta-lactam allergy due to high risk of subsequent Clostridioides (formerly Clostridium) difficile infection. A prolonged course is indicated; surgical intervention (eg, pneumonectomy, lobectomy) may be required in the rare cases that do not improve with antibiotic therapy. (Choice B) Pulmonary aspergillosis is seen primarily in immunocompromised patients and presents with fever, pleuritic pain, and hemoptysis. Imaging typically reveals a fungus ball within a cavity or nodules with surrounding ground-glass infiltrates (ie, halo sign), not consolidation with cavitation. fungus ball within a cavity (Choice C) Small cell lung cancer can cause hyponatremia due to release of antidiuretic hormone but would not cause cavitary lesions; in addition, fever, leukocytosis, and a short duration of symptoms would be uncommon. Squamous cell carcinoma can cause cavitary lung lesions; however, air-fluid levels are uncommon and a short duration of systemic symptoms would be atypical. (Choice D) Aspiration of gastric contents can result in chemical pneumonitis. Symptoms typically arise within hours (not a week) and include significant dyspnea and minimal fever. (Choice E) Pulmonary tuberculosis can cause fever, night sweats, and cavitary lung lesions. However, symptoms typically occur over several weeks or months; air-fluid levels (seen in 20% of cases of pulmonary tuberculosis) are more common with lung abscess; and marked leukocytosis and foul-smelling sputum are more suggestive of lung abscess. Educational objective: Lung abscess is usually due to the aspiration of oropharyngeal anaerobic bacteria. Patients with dysphagia or episodes of impaired consciousness (eg, drug or alcohol abuse) are at high risk. Symptoms include subacute fever, night sweats, weight loss, and cough with putrid sputum. X-ray reveals cavitary infiltrates, often with air-fluid levels. References: Lung abscess: update on microbiology and management. (http://www.ncbi.nlm.nih.gov/pubmed/22248872)

A 58-Year-Old Man Comes to the Emergency Department Due to a Week