A 43-year-old man with a history of active intravenous drug use comes to the emergency department with 2 weeks of malaise, dry cough, and increasing dyspnea on exertion. He admits to anorexia and a 5-kg (11-lb) weight loss over the past 3 weeks. About 2 hours ago, he felt sudden, sharp, right-sided chest pain and became acutely dyspneic. Pulse oximetry on ambulance arrival showed 80% on room air. The patient was started on 5 L O₂/min with notable improvement of saturation. He has known HIV and chronic hepatitis C infections but is not receiving any therapy. He smokes a pack of cigarettes daily and last sniffed heroin this morning.
His temperature is 37.2 C (99 F) , blood pressure is 136/88 mm Hg, pulse is 102/min, and respirations are 18/min. Pulse oximetry shows 94% on 4 L O₂/min. Examination shows a cachectic man in mild respiratory distress. The lymph nodes are not enlarged. There is a faint systolic murmur at the left sternal border and tachycardia. Decreased breath sounds are heard on the right with clear lungs on the left. There is hyperresonance to percussion on the right side of the chest. There is no peripheral edema or skin rashes.
Laboratory results are as follows:

Arterial blood gas analysis shows pH of 7.48, PCO₂ of 31 mm Hg, and PO₂ of 71 mm Hg.
Chest x-ray shows a 30% right-sided pneumothorax with bibasilar reticular opacities and a thin-walled cavitary lesion in the left upper lung field.
Which of the following is the most likely diagnosis?

Question

A 43-year-old man with a history of active intravenous drug use comes to the emergency department with 2 weeks of malaise, dry cough, and increasing dyspnea on exertion. He admits to anorexia and a 5-kg (11-lb) weight loss over the past 3 weeks. About 2 hours ago, he felt sudden, sharp, right-sided chest pain and became acutely dyspneic. Pulse oximetry on ambulance arrival showed 80% on room air. The patient was started on 5 L O₂/min with notable improvement of saturation. He has known HIV and chronic hepatitis C infections but is not receiving any therapy. He smokes a pack of cigarettes daily and last sniffed heroin this morning.
His temperature is 37.2 C (99 F) , blood pressure is 136/88 mm Hg, pulse is 102/min, and respirations are 18/min. Pulse oximetry shows 94% on 4 L O₂/min. Examination shows a cachectic man in mild respiratory distress. The lymph nodes are not enlarged. There is a faint systolic murmur at the left sternal border and tachycardia. Decreased breath sounds are heard on the right with clear lungs on the left. There is hyperresonance to percussion on the right side of the chest. There is no peripheral edema or skin rashes.
Laboratory results are as follows:

Arterial blood gas analysis shows pH of 7.48, PCO₂ of 31 mm Hg, and PO₂ of 71 mm Hg.
Chest x-ray shows a 30% right-sided pneumothorax with bibasilar reticular opacities and a thin-walled cavitary lesion in the left upper lung field.
Which of the following is the most likely diagnosis?

Quizplus · Accepted Answer

This patient with HIV likely has Pneumocystis jirovecii pneumonia (PCP) complicated by pneumothorax. A subacute course with dyspnea, dry cough, and fever is classic for PCP. Other symptoms include chest pain, malaise, weight loss, headache, night sweats, chills, and fatigue. Of AIDS patients with PCP, 6%-7% may be asymptomatic. Lack of fever (as in this patient) does not exclude PCP, although it does make a bacterial or mycobacterial source less likely. Nearly 90% of patients have lactate dehydrogenase (LDH) levels >50 U/L above baseline; an LDH >450 U/L is predictive of PCP rather than another pulmonary process. Arterial blood gas analysis usually shows hypoxemia, an increased alveolar-arterial oxygen gradient, and respiratory alkalosis. The most commonly described radiographic appearance in PCP is interstitial infiltrates (unilateral, bilateral, or diffuse), although a normal chest x-ray can be seen. Thin-walled cavitary lesions may be present. Spontaneous pneumothorax develops in approximately 5% of PCP patients. Pneumothorax is thought to develop primarily in the setting of rupture of cystic lesions that may be present in active disease or remaining from an earlier infection. (Choices A and E) Many of this patient's symptoms are also features of mycobacterial infection. However, the constellation of pneumothorax, LDH >450 U/L, relatively short duration of symptoms, lack of documented fevers, and thin-walled cavity on radiograph makes PCP more likely. (Choice C) Chronic necrotizing pulmonary aspergillosis is a subacute infection most commonly seen in patients with altered local defenses from pre-existing pulmonary disease or those with risk factors that alter systemic immune status. This infection is less likely given the lack of "fungus ball" appearance on chest x-ray and the likely only mild pre-existing pulmonary disease. (Choice D) Staphylococcal lung abscess can be seen in patients with septic emboli from endocarditis. This patient has a pneumothorax and not the multiple thick-walled cavities typical of septic emboli; he also has no fever or elevated white blood cell count. Educational objective: Nearly 90% of patients with Pneumocystis jirovecii pneumonia (PCP) will have lactic acid dehydrogenase levels >50 U/L above baseline; a level >450 U/L is predictive of PCP rather than another pulmonary process. The most commonly described radiographic appearance in PCP is diffuse interstitial infiltrates. Spontaneous pneumothorax develops in approximately 5% of patients. __________ References: HIV-associated opportunistic pneumonias. (http://www.ncbi.nlm.nih.gov/pubmed/19645867) HIV-associated Pneumocystis pneumonia. (http://www.ncbi.nlm.nih.gov/pubmed/21653531)

A 43-Year-Old Man with a History of Active Intravenous Drug