Differential Diagnosis
- Single most likely diagnosis
- C) Severe combined immunodeficiency (SCID): The patient's presentation with severe respiratory infection, low leukocyte count, and significantly decreased CD3+, CD4+, and undetectable CD8+ T-lymphocyte counts, along with undetectable IgG and low IgM levels, points towards a severe immunodeficiency. SCID is characterized by a profound deficiency in T-cell function, which can lead to severe infections early in life, consistent with this patient's symptoms.
- Other Likely diagnoses
- B) HIV infection: Although less likely given the age and lack of specific risk factors mentioned, HIV infection can cause immunodeficiency and lead to similar laboratory findings, including low CD4+ T-cell counts and impaired immune function.
- E) X-linked agammaglobulinemia: This condition, also known as Bruton's agammaglobulinemia, is characterized by low levels of B cells and immunoglobulins, leading to recurrent infections. However, it typically presents with infections after 6 months of age, once maternal antibodies have waned, and primarily affects males.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- B) HIV infection: It's crucial to consider HIV infection due to its severe implications on the immune system and the potential for vertical transmission from mother to child. Early diagnosis and treatment of HIV are critical for the child's prognosis.
- Rare diagnoses
- A) Common variable immunodeficiency: This condition typically presents later in life with recurrent infections and is characterized by impaired antibody production. It's less likely given the patient's age and the severity of the immunodeficiency presented.
- D) Transient agammaglobulinemia of infancy: This is a temporary condition where there's a delay in the production of immunoglobulins. It's less likely given the patient's severe T-cell deficiency and the presence of a severe infection at a young age.