A 35-year-old man comes to the office due to 3 months of persistent cough and shortness of breath with exertion. The patient was treated for sinusitis 3 times and pneumonia twice in the past 2 years; symptoms improved after antibiotic therapy but recurred quickly thereafter. He has never smoked cigarettes and takes no medications. Temperature is 37 C (98.6 F), blood pressure is 110/78 mm Hg, pulse is 86/min, and respirations are 15/min. BMI is 23 kg/m². The oropharynx is clear. There is no lymphadenopathy or hepatosplenomegaly. Complete blood count, serum electrolytes, and renal function tests are normal. HIV testing is negative. CT scans reveal mucosal thickening of the paranasal sinuses and fibrosis at bilateral lung bases. What is the best next step in management of this patient?

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Explanation: 11ec25c8_d129_fed4_bc81_4f19257087ed_MD0003_00 This patient has recurrent sinopulmonary infections and chronic lung disease, findings suggestive of an immunoglobulin deficiency disorder. Symptom onset in young adulthood (age 20-40) is characteristic of common variable immunodeficiency (CVID), a primary humoral immunodeficiency in which antibody production is decreased because B cells cannot differentiate into plasma cells. The most common initial manifestations of CVID include acute and chronic rhinosinusitis, as seen on this patient's imaging. Patients may subsequently develop progressive cough and dyspnea due to restrictive or obstructive lung disease. Mechanisms for chronic lung disease include the following: Immune-mediated interstitial lung disease resulting in pulmonary fibrosis and scarring Bronchiectasis (ie, dilated, thickened airways) due to frequent infection and inflammation Other manifestations can include chronic gastrointestinal illness, autoimmune disorders, and atopic disease. The next step in evaluation of a humoral immunodeficiency is a quantitative immunoglobulin panel. Patients with CVID have low IgG in combination with low IgM and/or IgA. Antibody response to vaccines is also low in CVID, but leukocyte count is generally normal. Treatment is immunoglobulin replacement therapy and management of chronic lung disease. (Choice A) Bronchoalveolar lavage can be used to diagnose a primary lung disease (eg, pneumonia, malignancy). The presence of concomitant, chronic sinus disease in this patient makes an underlying immunodeficiency more likely. (Choice B) Flow cytometry may be considered in an infant or toddler with low immunoglobulin levels concerning for X-linked agammaglobulinemia, which is characterized by markedly low B cells. This patient's age makes this diagnosis unlikely. Flow cytometry is not required for the diagnosis of CVID but typically reveals normal B and T lymphocytes. (Choice C) Alpha-1 antitrypsin deficiency is characterized by tissue damage in the lungs and liver. The sinuses are not involved, and CT scan would reveal emphysematous changes (eg, large air spaces) rather than fibrosis in the lower lungs. (Choice E) Sputum culture for acid-fast bacilli is diagnostic for Mycobacterium tuberculosis, which can cause chronic pulmonary infection but very rarely affects the sinuses. Classic x-ray findings of pulmonary tuberculosis include consolidation, cavitation, hilar adenopathy, and pleural effusions. Educational objective: Recurrent sinopulmonary infections and evidence of chronic lung disease (eg, bronchiectasis, fibrosis/scarring) in a young adult are suspicious for an underlying immunoglobulin deficiency such as common variable immunodeficiency. References: CT screening for pulmonary pathology in common variable immunodeficiency disorders and the correlation with clinical and immunological parameters. (http://www.ncbi.nlm.nih.gov/pubmed/24952009) Common variable immunodeficiency-associated granulomatous and interstitial lung disease. (http://www.ncbi.nlm.nih.gov/pubmed/23880700)

A 35-Year-Old Man Comes to the Office Due to 3