A 32-year-old woman comes to the office due to persistent cough and shortness of breath. She has had 3 episodes of pneumonia over the last 3 years. The patient had severe sinusitis a year ago and an episode of bloody diarrhea that required hospitalization 6 months ago. She usually responds to antibiotics but takes several days to clear the infection. No other family members have similar problems. The patient has not traveled outside of the United States. She does not use tobacco, alcohol, or illicit drugs and currently takes no medications. All of her immunizations are up to date. Blood pressure is 130/80 mm Hg and pulse is 90/min. BMI is 22 kg/m². Physical examination reveals fine crackles over the right lower lung field. No lower extremity edema is present. Neck palpation does not show any lymph node enlargement. Leukocyte count is 14,000/mm³. HIV testing is negative. Chest x-ray reveals a right lower lobe infiltrate. Which of the following is most likely to reveal the cause of this patient's underlying disease process?

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11ec25c8_d318_fe15_bc81_c5c10676fbc1_MD0003_00 This patient with evidence of acute pneumonia (cough, shortness of breath, leukocytosis, right lower lobe infiltrate) and recent history of recurrent pneumonia, sinusitis, and bloody diarrhea likely has common variable immunodeficiency (CVID). CVID is a collective diagnosis that includes a number of genetic defects resulting in impaired B cell differentiation and hypogammaglobulinemia. CVID is one of the most common primary immunodeficiencies in adults and is characterized mainly by increased susceptibility to bacterial infection. Recurrent respiratory infections (eg, pneumonia, sinusitis, otitis) and gastrointestinal infections (eg, Salmonella, Campylobacter) are common, and the latter may lead to episodes of bloody diarrhea. Chronic giardiasis may occur, but opportunistic infections (eg, Candida, Pneumocystis jirovecii) are rare. Other characteristics of CVID include concomitant autoimmune disease (eg, hemolytic anemia, rheumatoid arthritis, pernicious anemia), inflammatory bowel-like disease, granuloma development, and increased risk for non-Hodgkin lymphoma. Enteropathy (eg, sprue-like illness) is common, and affected patients may present with malabsorption and weight loss. Most cases of CVID are due to sporadic mutation, and family history of the disease is typically absent (as in this patient). The majority of patients are diagnosed in adulthood (age 20-45) due to a combination of variable presentation and diagnostic delay. Diagnosis is made by quantitative measurement of immunoglobulin levels (significantly reduced serum IgG with low levels of IgA and/or IgM) as well as by markedly reduced or absent immune response to vaccination. (Choice A) Low CD4+ lymphocyte counts occur in DiGeorge syndrome and HIV infection and create susceptibility to opportunistic infection. DiGeorge syndrome typically manifests shortly after birth, and this patient is HIV negative. (Choice B) Alpha-1 antitrypsin deficiency is an inherited disorder that leads to emphysema and liver damage but does not increase the risk of recurrent infections. (Choice C) Methacholine challenge is used to diagnose asthma, which is not characterized by recurrent bacterial respiratory infections. (Choice E) Sweat chloride test is used to diagnose cystic fibrosis (CF). Recurrent pneumonia and sinusitis can occur in CF; however, CF is often diagnosed prior to adulthood. In addition, although diarrhea and malabsorption may be seen (due to pancreatic insufficiency), bloody diarrhea would be unusual. Educational objective: Recurrent bacterial infections in an adult should raise suspicion for common variable immunodeficiency. Quantitative measurement of serum immunoglobulin levels is needed to establish the diagnosis. References: Clinical picture and treatment of 2212 patients with common variable immunodeficiency. (http://www.ncbi.nlm.nih.gov/pubmed/24582312)

A 32-Year-Old Woman Comes to the Office Due to Persistent