A 34-year-old woman comes to the hospital after a day of sudden onset fever, chest tightness, dyspnea, and dry cough. The patient has been hospitalized twice in the past 3 months with similar symptoms. Both times she received antibiotic treatment for pneumonia and the symptoms resolved within 1-2 days. She does not use tobacco, alcohol, or illicit drugs. She has no known drug allergies. Temperature is 37.9 C (100 F), blood pressure is 128/80 mm Hg, pulse is 92/min, and respirations are 20/min. Pulse oximetry is 90% on room air. BMI is 29 kg/m². The patient is in mild respiratory distress. Examination shows normal jugular venous pressure, no lymphadenopathy, and normal heart sounds. Diffuse fine crackles are heard throughout both lung fields. Leukocytes are 11,200/mm³. CT scan of the chest reveals a bilateral micronodular interstitial pattern. Blood cultures are negative. Which of the following is the most likely diagnosis?

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11ec25c8_d4b4_856f_bc81_99d9b516e1a1_MD0003_00 This patient with recurrent, short-lived episodes of sudden-onset fever, nonproductive cough, and dyspnea most likely has hypersensitivity pneumonitis (HP), an exaggerated immunologic response to an inhaled antigen (eg, mold, bacteria, animal protein). The condition can have variable presentation (eg, acute or chronic) that likely depends on the dose and chronicity of antigen exposure. Acute HP classically presents with recurrent episodes of abrupt-onset fever, nonproductive cough, dyspnea, and fatigue that coincide with intermittent high-dose antigen exposure (eg, developing within hours of exposure). Hypoxemia is common and fine crackles are present on lung auscultation. Leukocytosis is also often present. Chest x-ray may be normal or can reveal scattered micronodular interstitial opacities that typically resolve between episodes. The condition is often mistaken for bacterial pneumonia and is treated with antibiotics; however, acute HP self-resolves within several hours to days after removal of antigen exposure. Long-term management requires consistent avoidance of the offending antigen, which can often but not always be identified with a detailed occupational/exposure history (eg, farming, textile). (Choice A) Patients with complement deficiency are susceptible to recurrent infections with encapsulated bacteria (eg, Streptococcus pneumoniae); however, such infections are often severe and unlikely to resolve within only a few days, even with antibiotics. (Choice B) Granulomatosis with polyangiitis is a small vessel vasculitis that primarily affects the respiratory tracts and kidneys. Although it can present with dyspnea and cough, it also commonly affects the upper respiratory tracts (eg, nasal crusting) and typically follows a more progressive course with systemic manifestations (eg, weight loss, fatigue). In addition, episodic disease flares require immunosuppression (eg, glucocorticoids) and would not resolve within 1-2 days with antibiotics. (Choice D) Idiopathic pulmonary fibrosis (IPF) presents with gradually progressive dyspnea, cough, fatigue, and weight loss (closely mimicking the presentation of chronic, but not acute, HP). Intermittent, short-lived episodes would be unusual. In addition, IPF typically affects patients age >50. (Choice E) Influenza pneumonia can present with symptoms and chest x-ray findings similar to acute HP. However, recurrent disease that presents abruptly and resolves within 1-2 days is not consistent with influenza, in which symptoms commonly take 2 weeks to resolve. Educational objective: Acute hypersensitivity pneumonitis classically presents with recurrent episodes of abrupt-onset fever, dyspnea, nonproductive cough, and fatigue that coincide with intermittent exposure to an inhaled antigen. The condition is often mistaken for bacterial pneumonia but self-resolves within a few days after removal of antigen exposure. References: Hypersensitivity pneumonitis. (http://www.ncbi.nlm.nih.gov/pubmed/29763093)

A 34-Year-Old Woman Comes to the Hospital After a Day