Differential Diagnosis
- Single most likely diagnosis + A) Common variable immunodeficiency: This diagnosis is the most likely due to the patient's history of recurrent infections (chronic sinusitis and pneumococcal pneumonia), low IgA levels, and normal CD3+, CD4+, and CD8+ T-lymphocyte counts. The patient's ability to mount an immune response, as evidenced by the elevated leukocyte count and presence of bands, suggests a humoral immunodeficiency rather than a combined immunodeficiency.
- Other Likely diagnoses + None: Based on the provided information, common variable immunodeficiency is the most fitting diagnosis. However, other immunodeficiencies could be considered if more information were available.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.) + C) Severe combined immunodeficiency: Although the patient's T-lymphocyte counts are normal, severe combined immunodeficiency (SCID) is a life-threatening condition that requires prompt diagnosis and treatment. SCID typically presents with more severe infections and earlier in life, but it should be considered in any patient with recurrent infections. + D) Systemic lupus erythematosus: While the patient's presentation is not typical for systemic lupus erythematosus (SLE), SLE can cause a wide range of symptoms, including recurrent infections. SLE is a potentially life-threatening condition that requires early diagnosis and treatment.
- Rare diagnoses + B) Mucocutaneous lymph node syndrome (Kawasaki disease): Kawasaki disease is an acute febrile illness that typically presents with rash, conjunctivitis, and lymphadenopathy. While the patient has a fever and elevated leukocyte count, the lack of other characteristic symptoms makes Kawasaki disease an unlikely diagnosis. + Other rare immunodeficiencies, such as IgG subclass deficiency or specific antibody deficiency, could also be considered, but they are less likely given the patient's low IgA levels and history of infections.