Differential Diagnosis for a 7-month-old Boy with Frequent Infections
- Single most likely diagnosis:
- Transient Hypogammaglobulinemia of Infancy (THI): This condition is characterized by low levels of immunoglobulins (IgG, IgA, and IgM) in infants, which can lead to an increased susceptibility to infections. The patient's low IgG level, normal development, and absence of other alarming signs support this diagnosis. The presence of tetanus-specific and diphtheria-specific IgG antibodies suggests that the patient has responded to vaccinations, which is consistent with THI.
- Other Likely diagnoses:
- IgG subclass deficiency: This condition involves a deficiency in one or more subclasses of IgG, which can increase the risk of infections. The patient's low IgG level could be indicative of an IgG subclass deficiency.
- Allergic dermatitis: The red, scaly lesions on the patient's cheeks could be indicative of an allergic reaction, which may be contributing to the patient's overall condition.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.):
- Severe Combined Immunodeficiency (SCID): Although the patient has responded to vaccinations, SCID is a life-threatening condition that requires prompt diagnosis and treatment. The absence of hepatosplenomegaly and the patient's normal development make SCID less likely, but it should not be entirely ruled out.
- HIV infection: HIV infection can cause immunodeficiency and increase the risk of infections. Although the patient's vaccinations have been effective, HIV testing may be necessary to rule out this possibility.
- Rare diagnoses:
- Wiskott-Aldrich Syndrome: This rare X-linked recessive disorder is characterized by eczema, thrombocytopenia, and immunodeficiency. Although the patient has red, scaly lesions, the absence of thrombocytopenia makes this diagnosis less likely.
- Hyper-IgM Syndrome: This condition involves a deficiency in CD40 ligand, leading to an inability to switch from IgM to other immunoglobulin isotypes. The patient's low IgG level and normal IgM level could be indicative of this condition, but further testing would be necessary to confirm the diagnosis.