A 7-month-old boy is brought to the physician by his parents due to irritability and white patches in his mouth. His past medical history is significant for 3 episodes of otitis media and 2 episodes of bronchiolitis that have required hospitalization. He also has a history of chronic loose stools. The child is small for his age and ill-appearing. Head and neck examination shows white patches consistent with oral candidiasis but is otherwise normal. Auscultation of the lungs shows expiratory wheezing. Cardiac examination is within normal limits. Laboratory results are as follows: Serum protein electrophoresis shows a very low gamma globulin level. Chest x-ray reveals an absent thymic shadow. Which of the following is the most likely diagnosis?

Question

A 7-month-old boy is brought to the physician by his parents due to irritability and white patches in his mouth.  His past medical history is significant for 3 episodes of otitis media and 2 episodes of bronchiolitis that have required hospitalization.  He also has a history of chronic loose stools.  The child is small for his age and ill-appearing.  Head and neck examination shows white patches consistent with oral candidiasis but is otherwise normal.  Auscultation of the lungs shows expiratory wheezing.  Cardiac examination is within normal limits.  Laboratory results are as follows:  Serum protein electrophoresis shows a very low gamma globulin level.  Chest x-ray reveals an absent thymic shadow.  Which of the following is the most likely diagnosis?

Quizplus · Accepted Answer

11ec160b_3a73_2a4c_9249_ff63ca0ce91e_MD0001_00 Severe combined immune deficiency (SCID) is a life-threatening immunodeficiency syndrome that presents in infancy. It is caused by a variety of mutations in different genes that result in impaired T and B cell development and function. This leads to compromised cell-mediated and humoral immunity with the eventual development of severe viral and bacterial infections as maternal immunity wanes. Other common features include mucocutaneous candidiasis, persistent diarrhea, and failure to thrive. Laboratory studies show very low or absent CD3+ T cells and hypogammaglobulinemia. Thymic hypoplasia or aplasia is another common finding in infants with SCID due to severe T cell deficiency. (Choice A) Common variable immunodeficiency is a heterogenous condition caused by B and T cell dysfunction and characterized by hypogammaglobulinemia. It presents with recurrent infections in adults and children (after the neonatal period). While not entirely unaffected, cell-mediated immunity is not as impaired as in SCID and thymic aplasia is unlikely. (Choice B) DiGeorge syndrome (DGS) classically presents with craniofacial abnormalities, conotruncal cardiac anomalies, hypoplastic thymus, and hypocalcemia resulting from parathyroid hypoplasia. Immunodeficiency can also occur and is related to the degree of thymic hypoplasia. Although complete DGS (<1% of cases) is a form of SCID, the absence of other characteristic findings makes DGS a less likely diagnosis. (Choice D) In Wiskott-Aldrich syndrome, functioning of both T and B cells is impaired due to abnormal cytoskeletal functioning. Patients experience recurrent viral, bacterial, and fungal infections that generally worsen with age. However, Wiskott-Aldrich syndrome also typically causes bleeding due to thrombocytopenia and eczema. (Choice E) X-linked (Bruton's) agammaglobulinemia is an immunodeficiency syndrome caused by insufficient production of mature B cells, which predisposes mainly to recurrent infections with encapsulated pyogenic bacteria (eg, Streptococcus pneumoniae, Hemophilus influenzae type B). The quantity and functioning of T cells is generally not affected, so an absent thymic shadow is unlikely. Educational objective: Severe combined immune deficiency is characterized by combined T and B cell dysfunction. It is a life-threatening condition that presents in infancy with severe bacterial and viral infections; mucocutaneous candidiasis; persistent diarrhea; and failure to thrive. Laboratory findings include absent T cells and hypogammaglobulinemia. The thymic shadow is not usually present due to severe T cell deficiency. __________ References: Educational paper. The expanding clinical and immunological spectrum of severe combined immunodeficiency. (http://www.ncbi.nlm.nih.gov/pubmed/21479529) Educational paper: Primary immunodeficiencies in children: a diagnostic challenge. (http://www.ncbi.nlm.nih.gov/pubmed/21170549) Clinical immunology review series: an approach to the patient with recurrent infections in childhood. (http://www.ncbi.nlm.nih.gov/pubmed/18373701)

A 7-Month-Old Boy Is Brought to the Physician by His