A 13-month-old boy is brought to the emergency department due to cough and increased work of breathing. The patient's parents immigrated to the United States when he was 6 months old. He has a history of recurrent otitis media, pneumonia, and thrush as well as chronic diarrhea and failure to thrive. On physical examination, he is tachypneic and has perioral cyanosis. A chest radiograph shows bilateral interstitial opacities. The patient is admitted to the hospital and undergoes bronchoscopy. Analysis of the bronchoalveolar lavage fluid reveals Pneumocystis jirovecii. Which of the following is the most likely underlying diagnosis?

Question

A 13-month-old boy is brought to the emergency department due to cough and increased work of breathing.  The patient's parents immigrated to the United States when he was 6 months old.  He has a history of recurrent otitis media, pneumonia, and thrush as well as chronic diarrhea and failure to thrive.  On physical examination, he is tachypneic and has perioral cyanosis.  A chest radiograph shows bilateral interstitial opacities.  The patient is admitted to the hospital and undergoes bronchoscopy.  Analysis of the bronchoalveolar lavage fluid reveals Pneumocystis jirovecii. Which of the following is the most likely underlying diagnosis?

Quizplus · Accepted Answer

11ec160b_37ba_7338_9249_fbce37dd3154_MD0001_00 Severe combined immunodeficiency (SCID) is a group of X-linked and autosomal recessive genetic disorders marked by the impaired development and activity of both T-lymphocytes and B-lymphocytes. Loss of T-lymphocyte activity results in deficient cell-mediated immunity, leading to recurrent viral, fungal, and opportunistic (eg, Pneumocystis jirovecii) infections. Because T-lymphocytes are required for B-cells to produce IgG and IgA (T-cell-induced immunoglobulin class switching), patients with SCID also have a dramatic impairment in humoral immunity; this is typically marked by recurrent sinopulmonary bacterial infections (eg, pneumonia, otitis media) and chronic diarrhea due to the lack of IgG and IgA. Recurrent infections often cause failure to thrive. Laboratory findings of SCID include lymphopenia and hypogammaglobulinemia. Stem cell transplant is the only treatment. (Choice A) Agammaglobulinemia is an isolated B cell defect that manifests with recurrent sinopulmonary bacterial infections. Infection with Pneumocystis jirovecii is not seen in isolated B cell defects because this infection is primarily countered by the cell-mediated immune response. (Choice B) Chronic granulomatous disease is a disorder of phagocyte dysfunction due to defective NADPH oxidase. This predisposes to infection with certain bacterial (eg, Staphylococcus aureus) and fungal (eg, Aspergillus) organisms; skin abscesses, pneumonia, and osteomyelitis are common. (Choice C) Cystic fibrosis is an autosomal recessive disease characterized by thick airway secretions and pancreatic insufficiency, which result in recurrent respiratory infections and chronic diarrhea, respectively. Pneumocystis and thrush would not be expected. (Choice D) Primary ciliary dyskinesia is an autosomal recessive disease that results in poor mucociliary function in the respiratory tract, middle ear, and reproductive organs. Affected patients have recurrent sinopulmonary infections in childhood and decreased fertility in adulthood. Viral or opportunistic infections are not seen. (Choice F) Terminal complement deficiency (any of C5-C9) prevents formation of the membrane attack complex and results in increased susceptibility to infections by Neisseria. Educational objective: Severe combined immunodeficiency is caused by a genetic defect in T cell development, leading to loss of both cellular and humoral immunity. Patients present in infancy with recurrent bacterial, viral, fungal, and opportunistic infections as well as failure to thrive and chronic diarrhea. __________ References: Evaluation of primary immunodeficiency disease in children. (http://www.ncbi.nlm.nih.gov/pubmed/23939499)

A 13-Month-Old Boy Is Brought to the Emergency Department Due