A 3-year-old boy is brought to the emergency department due to fever and respiratory distress. Medical history includes recurrent otitis media and a hospitalization for pneumonia. Immunizations are up to date. Height and weight are at the 40th percentile for age. Temperature is 39.5 C (103.1 F), blood pressure is 90/60 mmHg, pulse is 140/min, and respirations are 38/min. He is drooling and has marked stridor. Emergency intubation is performed, and an inflamed epiglottis is noted. Antibiotics are administered; blood culture grows Haemophilus influenzae type b. Laboratory results show deficient serum-specific antibody titers to tetanus, diphtheria, H influenzae type b, and pneumococcus. What additional testing is indicated in this patient?

Question

A 3-year-old boy is brought to the emergency department due to fever and respiratory distress.  Medical history includes recurrent otitis media and a hospitalization for pneumonia.  Immunizations are up to date.  Height and weight are at the 40th percentile for age.  Temperature is 39.5 C (103.1 F), blood pressure is 90/60 mmHg, pulse is 140/min, and respirations are 38/min.  He is drooling and has marked stridor.  Emergency intubation is performed, and an inflamed epiglottis is noted.  Antibiotics are administered; blood culture grows Haemophilus influenzae type b.  Laboratory results show deficient serum-specific antibody titers to tetanus, diphtheria, H influenzae type b, and pneumococcus.  What additional testing is indicated in this patient?

Quizplus · Accepted Answer

11ec25c8_d62d_4316_bc81_f169bdff2508_MD0003_00 This patient with a history of recurrent infections now has epiglottitis due to Haemophilus influenzae type b infection. In a fully immunized child, infection with this bacterium is concerning for humoral immunodeficiency, such as X-linked agammaglobulinemia (XLA), or Bruton agammaglobulinemia. A defect in Bruton tyrosine kinase prevents pre-B cells from maturing and exiting the bone marrow, which results in low levels of circulating plasma cells and decreased antibody production. pre-B cells Patients with XLA are predisposed to recurrent sinopulmonary infections (eg, acute otitis media, pneumonia) by encapsulated bacteria (eg, Streptococcus pneumoniae, H influenzae type b) because antibody opsonization is required for phagocytosis. Gastrointestinal and enteroviral infections are also common. Characteristic laboratory findings in XLA include low levels of all immunoglobulins as well as deficient antibody response to vaccines, as seen here. Flow cytometry of peripheral blood is performed to determine the affected lymphocyte subpopulation and shows markedly reduced CD19⁺ B cells in patients with XLA. Genetic testing confirms the diagnosis. Life-long immunoglobulin replacement therapy reduces the rate and severity of infections. (Choices A and D) Abdominal ultrasonography can assess for asplenia, which increases the risk of infection with encapsulated organisms due to impaired phagocytosis by splenic macrophages. Similarly, sickle cell disease (characterized by abnormal hemoglobin electrophoresis) increases infection risk due to functional asplenia from repeated splenic infarction. Vaccine antibody response is normal with anatomic or functional asplenia. (Choice B) Intradermal injection of Candida antigen normally elicits a type IV hypersensitivity reaction that confirms intact T-lymphocyte function. Testing should be performed if a patient's history suggests T-cell dysfunction (eg, severe viral or fungal infections). However, this patient's poor vaccine antibody response suggests B-lymphocyte dysfunction. (Choice E) Neutrophil respiratory burst is impaired in chronic granulomatous disease, which presents with recurrent skin and pulmonary infections with catalase-positive organisms (eg, Staphylococcus aureus, Serratia marcescens). Antibody production is not affected. (Choice F) Complement deficiency should be suspected in a patient with recurrent Neisseria infections. Low antibody titers to vaccines are not expected. Educational objective: X-linked agammaglobulinemia should be suspected in a fully immunized child who has Haemophilus influenzae type b infection. Laboratory studies reveal low immunoglobulin levels with deficient antibody response to vaccines as well as markedly reduced CD19⁺ B lymphocytes on flow cytometry. References: X-linked agammaglobulinemia. (http://www.ncbi.nlm.nih.gov/pubmed/31751055)

A 3-Year-Old Boy Is Brought to the Emergency Department Due