Immunodeficiencies: Clinical

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Immunodeficiencies: Clinical

USMLE® Step 2 questions

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USMLE® Step 2 style questions USMLE

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A newborn boy is admitted to the neonatal intensive care unit for cyanosis after being born to a 30-year-old woman via a normal vaginal delivery at 38 weeks gestation. The mother had poor prenatal care and follow up. Temperature is 38.7 C (101.7 F), pulse is 90/min, respirations are 35/min, and blood pressure is 80/40 mmHg. Pulse oximetry shows 80% oxygen saturation on room air. Physical examination demonstrates a hypoplastic mandible, cleft palate, orbital hypertelorism, and bifid uvula. Chest x-ray shows decreased soft tissue attenuation in the right anterior mediastinum. Echocardiographic findings are consistent with Tetralogy of Fallot. A genetic disorder with pure T-cell dysfunction is suspected. Which of the following modalities would be most useful to confirm the genetic abnormality underlying this patient’s condition?


Immunodeficiencies can be classified into primary and secondary immunodeficiencies.

Primary immunodeficiencies are relatively rare, genetic and typically inherited defects in one or more of the elements of the immune system.

Secondary immunodeficiencies are much more common, acquired disorders that occur as a result of some extrinsic factor affecting the immune system.

Both primary and secondary immunodeficiencies can cause frequent or recurrent infections- specifically six or more new infections anywhere in the body within one year or four or more new ear infections within one year. Sometimes these infections turn out to be unusually severe.

Specifically, it’s unusual for two or more serious sinus infections or pneumonias to occur within one year or two or more episodes of sepsis or meningitis to occur in a lifetime.

Serious means that they cause persistent fever or confinement to bed for a week or more, are difficult to treat requiring two or more months of antibiotics with little effect or a need for IV antibiotics or hospitalization or cause unusual complications.

These include organ abscesses, non healing wounds, chronic diarrhea or failure to thrive meaning failure to gain weight or grow normally, persistent laboratory abnormalities such as leukocytosis or elevated ESR and CRP or persistent imaging abnormalities, such as bronchiectasis.

And then, it’s also concerning if the pathogens are opportunistic organisms, such as Candida albicans, nontuberculous Mycobacteria or Pneumocystis jiroveci, which usually don’t cause serious infections in individuals with a normal immune system.

Okay, now secondary immunodeficiencies usually occur well after infancy while most primary immunodeficiencies are inherited and present during the first few years.

Secondary immunodeficiencies can be caused by underlying diseases like HIV infection, malnutrition, diabetes mellitus, malignancy, splenectomy, for example due to sickle cell disease, trauma or previous surgery, ionizing radiation and immunosuppressive medications. Treatment is based on controlling the underlying disease or stopping the offending medication.


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