A 2-year-old boy is brought to the office due to recurrent infections. He was born at term after an uncomplicated pregnancy. His mother states, "My boy is always sick with something and is constantly on antibiotics." The patient has had multiple episodes of otitis media, skin infections, and pneumonia. Incision and drainage of his skin infections revealed Staphylococcus aureus on bacterial culture but no purulence. The infections usually resolve with prolonged antibiotic courses. Laboratory testing reveals absent CD18 antigens on the surface of leukocytes. This patient's underlying condition is most likely associated with which of the following?

Question

A 2-year-old boy is brought to the office due to recurrent infections.  He was born at term after an uncomplicated pregnancy.  His mother states, "My boy is always sick with something and is constantly on antibiotics."  The patient has had multiple episodes of otitis media, skin infections, and pneumonia.  Incision and drainage of his skin infections revealed Staphylococcus aureus on bacterial culture but no purulence.  The infections usually resolve with prolonged antibiotic courses.  Laboratory testing reveals absent CD18 antigens on the surface of leukocytes.  This patient's underlying condition is most likely associated with which of the following?

Quizplus · Accepted Answer

11ec160b_37e4_429a_9249_9d8ccde57e61_MD0001_00 This patient's recurring skin and mucosal infections, as well as the absence of purulence, are highly suggestive of leukocyte adhesion deficiency (LAD). LAD is an autosomal recessive disorder characterized by the absence of CD18 antigens, which are necessary for the formation of integrins. Integrins are essential for leukocyte adhesion to endothelial surfaces and migration into peripheral tissues in response to infection or inflammation. The failure of leukocyte chemotaxis results in characteristic LAD findings, including recurrent skin and mucosal infections (often due to Staphylococcus aureus or gram-negative rods) and periodontal disease. LAD-related infections are notable for lack of purulence because of the absence of leukocytes in peripheral tissues. Wound healing is also impaired, which can result in late umbilical cord separation (age >3 weeks). Peripheral leukocytosis and neutrophilia are typical, particularly during active infection, because leukocytes cannot migrate out of the blood vessels. (Choice A) Deficiencies of T-cell-mediated immunity (eg, HIV, severe combined immunodeficiency) increase the risk of infection following live vaccines. T-cell deficiencies present with severe opportunistic infections in early infancy but have normal CD18 antigens. (Choice B) Terminal complement deficiency (C5b-C9) results in an inability to form the membrane attack complex and predisposes to recurrent Neisseria infections. CD18 is not affected by this condition, and Neisseria infections are not common in LAD. (Choice D) The absence of B lymphocytes in X-linked agammaglobulinemia leads to hypoplasia of lymphoid tissue (eg, tonsils, lymph nodes). Patients have recurrent sinopulmonary infections, but nonpurulent skin infections and absence of CD18 are inconsistent with the diagnosis. (Choice E) Wiskott-Aldrich syndrome is an X-linked disorder characterized by the triad of thrombocytopenia, immunodeficiency, and eczema. It is caused by a defect in cytoskeleton rearrangement, not by CD18 deficiency. Educational objective: Leukocyte adhesion deficiency is due to the absence of CD18 antigens, which are necessary for the formation of integrins. Failure of leukocyte adhesion and migration results in recurrent skin and mucosal infections without purulence, delayed umbilical cord separation, and peripheral leukocytosis.

A 2-Year-Old Boy Is Brought to the Office Due to Recurrent