A 10-year-old girl with previously diagnosed sickle cell anemia presents to the emergency room with a low-grade fever, malaise, petechiae on her arms, and a rash on her face. She regularly takes hydroxyurea and receives blood transfusions to treat her condition. Her blood tests show a hemoglobin of 4.0 g/dL, MCV of 87 fl, and 2% reticulocyte count. An attempted bone marrow biopsy was a dry, empty tap. What is the most likely diagnosis?
Q142
A previously healthy 5-year-old boy is brought to the emergency department because of a 1-day history of high fever. His temperature prior to arrival was 40.0°C (104°F). There is no family history of serious illness. Development has been appropriate for his age. He is administered rectal acetaminophen. While in the waiting room, he becomes unresponsive and starts jerking his arms and legs back and forth. A fingerstick blood glucose concentration is 86 mg/dL. After 5 minutes, he continues having jerky movements and is unresponsive to verbal and painful stimuli. Which of the following is the most appropriate next step in management?
Q143
A 6-month-old male presents for a routine visit to his pediatrician. Two months ago, the patient was seen for tachypnea and wheezing, and diagnosed with severe respiratory syncytial virus (RSV) bronchiolitis. After admission to the hospital and supportive care, the patient recovered and currently is not experiencing any trouble breathing. Regarding the possibility of future reactive airway disease, which of the following statements is most accurate?
Q144
A 10-year-old boy is brought to the pediatric clinic because of persistent sinus infections. For the past 5 years, he has had multiple sinus and upper respiratory infections. He has also had recurrent diarrhea throughout childhood. His temperature is 37.0°C (98.6°F), the heart rate is 90/min, the respirations are 16/min, and the blood pressure is 125/75 mm Hg. Laboratory studies show abnormally low levels of one immunoglobulin isotype but normal levels of others. Which of the following is the most likely diagnosis?
Q145
A 5-year-old boy is brought to the physician by his parents because of a 6-week history of increased tiredness, irritability, and worsening leg pain. His parents report that he has been reluctant to walk recently because of the pain in his legs. Examination shows conjunctival pallor and diffuse petechiae. There are palpable, nontender posterior cervical and axillary lymph nodes. His hemoglobin concentration is 8.9 g/dL, leukocyte count is 45,750/mm3, and platelet count is 25,000/mm3. A bone marrow aspiration shows numerous immature cells that stain positive for CD10, CD19, and terminal deoxynucleotidyl transferase (TdT). Which of the following translocations is associated with a favorable prognosis for this patient's condition?
Q146
A 10-month-old boy is admitted to the pediatric intensive care ward because of progressive dyspnea and fever. For the past 2 weeks, he was unsuccessfully treated for an upper respiratory tract infection with ampicillin. He has a history of neonatal sepsis, frequent respiratory tract infections since the age of 3 months, and recurrent otitis media. He was born full-term vaginally to a consanguineous couple from an uncomplicated pregnancy. He received routine immunizations until 6 months of age. The patient’s vital signs are as follows: blood pressure is 70/40 mm Hg, heart rate is 138/min, respiratory rate is 39/min, and temperature is 39.5℃ (103.1 ℉). Physical examination reveals cyanosis, nasal flare, intercostal retractions, and bilaterally decreased breath sounds with crackles heard over the lower lobes on auscultation. The chest X-ray confirms bilateral lower lobe pneumonia. The blood count shows the following findings:
Erythrocytes 4.1 x 106/mm3
Hgb 13 g/dL
Total leukocyte count 41,100/mm3
Neutrophils 74%
Lymphocytes 14%
Eosinophils 2%
Monocytes 10%
Basophils 0%
Platelet count 210,000/mm3
The patient is diagnosed with bilateral community-acquired lower lobe pneumonia and prescribed antibiotics. An immunological workup is performed to assess the patient’s immunity:
Measurement Result Normal range
Antibodies
Total serum IgG 22.0 mg/dL 231–1,411 mg/dL
Serum IgA 59.3 mg/dL 0–83 mg/dL
Serum IgM 111.9 mg/dL 0–145 mg/dL
Lymphocyte flow cytometry
CD3+ cells 2.2% 60–85%
CD19+ cells 95.1% 8–20%
CD16/CD56+ cells 0.1% 3–30%
Which of the following procedures is the option of choice for the further management of this patient?
Q147
A 6-year-old girl is brought to the physician because of a 4-day history of irritation and redness in both eyes. Her symptoms initially started in the left eye and progressed to involve both eyes within 24 hours. She presents with profuse tearing and reports that her eyes are sticky and difficult to open in the morning. She was diagnosed with asthma 2 years ago and has been admitted to the hospital for acute exacerbations 3 times since then. Current medications include inhaled beclomethasone, inhaled albuterol, and montelukast. Her temperature is 38.2 °C (100.8°F). Physical examination reveals a tender left preauricular lymph node. There is chemosis and diffuse erythema of the bulbar conjunctiva bilaterally. Slit lamp examination reveals a follicular reaction in both palpebral conjunctivae and diffuse, fine epithelial keratitis of both corneas. Corneal sensation is normal. Which of the following is the most appropriate next step in management?
Q148
A 2-year-old boy is brought to the physician by his mother for evaluation of recurrent infections and easy bruising. He has been hospitalized 3 times for severe skin and respiratory infections, which responded to treatment with antibiotics. Examination shows sparse silvery hair. The skin is hypopigmented and there are diffuse petechiae. Laboratory studies show a hemoglobin concentration of 8 g/dL, leukocyte count of 3000/mm3, and platelet count of 45,000/mm3. A peripheral blood smear shows giant cytoplasmic granules in granulocytes and platelets. Which of the following is the most likely underlying cause of this patient's symptoms?
Q149
A 9-year-old boy is brought to the emergency department for the evaluation of diarrhea and vomiting for the last 2 days. During this period, he has had about 12 watery, non-bloody bowel movements and has vomited three times. He came back from a trip to India 3 days ago, where he and his family were visiting relatives. He has not been able to eat anything since the symptoms started. The patient has not urinated since yesterday. He appears pale. His temperature is 38°C (100.4°F), pulse is 106/min, and blood pressure is 96/60 mm Hg. Examination shows dry mucous membranes. The abdomen is soft with no organomegaly. Bowel sounds are hyperactive. Laboratory studies show:
Hemoglobin 13 g/dL
Serum
Na+ 148 mEq/L
Cl- 103 mEq/L
K+ 3.7 mEq/L
HCO3- 19 mEq/L
Urea nitrogen 80 mg/dL
Glucose 90 mg/dL
Creatinine 2 mg/dL
Intravenous fluid resuscitation is begun. Which of the following is the most likely cause of this patient's abnormal renal laboratory findings?
Q150
A 13-month-old boy with sickle cell anemia is brought to the emergency department because of continuous crying and severe left-hand swelling. His condition started 2 hours earlier without any preceding trauma. The child was given diclofenac syrup at home with no relief. The temperature is 37°C (98.6°F), blood pressure is 100/60 mm Hg, and pulse is 100/min. The physical examination reveals swelling and tenderness to palpation of the left hand. The hemoglobin level is 10.4 g/dL. Which of the following is the best initial step in management of this patient condition?
Infectious Disease US Medical PG Practice Questions and MCQs
Question 141: A 10-year-old girl with previously diagnosed sickle cell anemia presents to the emergency room with a low-grade fever, malaise, petechiae on her arms, and a rash on her face. She regularly takes hydroxyurea and receives blood transfusions to treat her condition. Her blood tests show a hemoglobin of 4.0 g/dL, MCV of 87 fl, and 2% reticulocyte count. An attempted bone marrow biopsy was a dry, empty tap. What is the most likely diagnosis?
A. Reaction to the blood transfusions
B. Gastrointestinal bleeding
C. Anemia of chronic disease
D. Aplastic crisis (Correct Answer)
E. Sequestration crisis
Explanation: ***Aplastic crisis***
- The combination of **severe anemia** (hemoglobin 4.0 g/dL), **low reticulocyte count** (2%), and a **dry bone marrow tap** confirms a defect in red blood cell production.
- In a patient with **sickle cell anemia**, an aplastic crisis is often triggered by **Parvovirus B19 infection**, which targets erythroid precursors.
*Reaction to the blood transfusions*
- An acute transfusion reaction would typically present with fever, chills, urticaria, or dyspnea, which are not the predominant symptoms here.
- Hemoglobin would likely drop acutely or remain stable, but not necessarily with such a profound reticulocytopenia or bone marrow findings.
*Gastrointestinal bleeding*
- While GI bleeding can cause severe anemia, it would typically be associated with **microcytic anemia** (decreased MCV if chronic) and **elevated reticulocyte count** as the bone marrow tries to compensate, neither of which are observed.
- There is no mention of melena or hematochezia, and the dry bone marrow tap points to a production problem, not blood loss.
*Anemia of chronic disease*
- This condition typically results in **mild to moderate anemia** with a **normal or slightly reduced MCV** and a **low reticulocyte count**.
- However, the hemoglobin level of 4.0 g/dL is too severe for typical anemia of chronic disease, and the dry bone marrow tap is not a characteristic finding.
*Sequestration crisis*
- A sequestration crisis involves the rapid pooling of blood in the spleen or liver, leading to **acute severe anemia** and often **splenomegaly**.
- However, it would be characterized by a **high reticulocyte count** as the bone marrow attempts to compensate for the sudden blood loss, which is contrary to the findings in this case.
Question 142: A previously healthy 5-year-old boy is brought to the emergency department because of a 1-day history of high fever. His temperature prior to arrival was 40.0°C (104°F). There is no family history of serious illness. Development has been appropriate for his age. He is administered rectal acetaminophen. While in the waiting room, he becomes unresponsive and starts jerking his arms and legs back and forth. A fingerstick blood glucose concentration is 86 mg/dL. After 5 minutes, he continues having jerky movements and is unresponsive to verbal and painful stimuli. Which of the following is the most appropriate next step in management?
A. Intravenous administration of lorazepam (Correct Answer)
B. Intravenous administration of phenobarbital
C. Obtain blood cultures
D. Intravenous administration of valproate
E. Intravenous administration of fosphenytoin
Explanation: ***Intravenous administration of lorazepam***
- The child is experiencing a **prolonged seizure** (greater than 5 minutes) following a high fever, which is concerning for **status epilepticus** secondary to a febrile seizure.
- **Lorazepam** is a first-line benzodiazepine for status epilepticus due to its rapid onset of action and prolonged anticonvulsant effect.
*Intravenous administration of phenobarbital*
- **Phenobarbital** is a long-acting anticonvulsant often used for **refractory status epilepticus** or as a long-term maintenance therapy.
- It is not the preferred initial treatment for an acute, prolonged seizure due to its slower onset compared to benzodiazepines.
*Obtain blood cultures*
- While obtaining blood cultures is important for identifying potential sources of infection causing the fever, it is **not the immediate priority** when a child is actively seizing and unresponsive.
- **Seizure termination** takes precedence to prevent potential neurological injury.
*Intravenous administration of valproate*
- **Valproate** is an anticonvulsant that can be used for various seizure types, but it is typically reserved for **refractory status epilepticus** or as a long-term maintenance drug.
- It does not have the rapid onset of action required for initial management of an acute, prolonged seizure.
*Intravenous administration of fosphenytoin*
- **Fosphenytoin** is an antiepileptic drug often used for **refractory status epilepticus** after benzodiazepines have failed.
- It is not the first-line medication for the initial management of an acute seizure of this duration.
Question 143: A 6-month-old male presents for a routine visit to his pediatrician. Two months ago, the patient was seen for tachypnea and wheezing, and diagnosed with severe respiratory syncytial virus (RSV) bronchiolitis. After admission to the hospital and supportive care, the patient recovered and currently is not experiencing any trouble breathing. Regarding the possibility of future reactive airway disease, which of the following statements is most accurate?
A. “There is no clear relationship between RSV and the development of asthma.”
B. “Your child has a greater than 20% chance of developing asthma” (Correct Answer)
C. “Your child’s risk of asthma is less than the general population.”
D. “Your child has a less than 5% chance of developing asthma”
E. “Your child’s risk of asthma is the same as the general population.”
Explanation: ***“Your child has a greater than 20% chance of developing asthma”***
- Severe **RSV bronchiolitis** in infancy is a significant risk factor for the development of **recurrent wheezing** and **childhood asthma**.
- Studies estimate that a substantial proportion, often greater than 20%, of infants with severe RSV bronchiolitis will go on to develop **asthma** later in childhood.
*“There is no clear relationship between RSV and the development of asthma.”*
- This statement is incorrect as there is a **well-established link** between severe RSV infection in early life and an increased risk of developing **asthma**.
- Numerous epidemiological and longitudinal studies have documented this association.
*“Your child’s risk of asthma is less than the general population.”*
- This is incorrect, as severe RSV infection **increases** the risk of asthma, not decreases it.
- Children with a history of severe RSV have a **higher incidence** of asthma compared to the general pediatric population.
*“Your child has a less than 5% chance of developing asthma”*
- This percentage is **too low** given the known association between severe RSV bronchiolitis and subsequent asthma.
- The actual risk is considerably higher, typically falling into the range of 20-50% for those with severe RSV.
*“Your child’s risk of asthma is the same as the general population.”*
- This statement is inaccurate because severe RSV infection in infancy is a recognized independent **risk factor** for **asthma development**.
- Therefore, the child's risk is elevated above that of the general population.
Question 144: A 10-year-old boy is brought to the pediatric clinic because of persistent sinus infections. For the past 5 years, he has had multiple sinus and upper respiratory infections. He has also had recurrent diarrhea throughout childhood. His temperature is 37.0°C (98.6°F), the heart rate is 90/min, the respirations are 16/min, and the blood pressure is 125/75 mm Hg. Laboratory studies show abnormally low levels of one immunoglobulin isotype but normal levels of others. Which of the following is the most likely diagnosis?
A. Chediak-Higashi syndrome
B. Selective IgA deficiency (Correct Answer)
C. Common variable immunodeficiency
D. Drug-induced IgA deficiency
E. Transient hypogammaglobulinemia of infancy
Explanation: ***Selective IgA deficiency***
- This condition is characterized by **abnormally low levels of IgA** with normal levels of other immunoglobulins, leading to recurrent **respiratory and gastrointestinal infections**.
- The patient's history of persistent sinus infections, upper respiratory infections, and recurrent diarrhea is highly consistent with the mucosal immune defects seen in IgA deficiency.
*Chediak-Higashi syndrome*
- This syndrome is a rare autosomal recessive disorder characterized by **partial oculocutaneous albinism**, recurrent pyogenic infections, and neurological abnormalities due to defective lysosomal trafficking.
- While it involves recurrent infections, the clinical picture does not include the characteristic features like albinism, nor does it typically present as an isolated IgA deficiency.
*Common variable immunodeficiency*
- This involves **low levels of IgG and IgA**, and sometimes IgM, leading to recurrent infections, particularly bacterial infections of the respiratory and gastrointestinal tracts.
- The patient's lab results specifically mention abnormally low levels of **one immunoglobulin isotype** (IgA), which differentiates it from CVID where multiple isotypes are low.
*Drug-induced IgA deficiency*
- While certain medications can cause IgA deficiency, the patient's symptoms have been persistent for 5 years, suggesting a **hereditary or primary immunodeficiency** rather than a transient drug-induced effect without a clear history of causative drug use.
- Common drugs causing IgA deficiency include phenytoin or D-penicillamine, which are not mentioned in the patient's history.
*Transient hypogammaglobulinemia of infancy*
- This condition typically resolves by **2-3 years of age** as the infant's immune system matures and starts producing its own antibodies.
- The patient is 10 years old, and his symptoms have persisted for 5 years, making this diagnosis unlikely due to the persistent nature of the deficiency at this age.
Question 145: A 5-year-old boy is brought to the physician by his parents because of a 6-week history of increased tiredness, irritability, and worsening leg pain. His parents report that he has been reluctant to walk recently because of the pain in his legs. Examination shows conjunctival pallor and diffuse petechiae. There are palpable, nontender posterior cervical and axillary lymph nodes. His hemoglobin concentration is 8.9 g/dL, leukocyte count is 45,750/mm3, and platelet count is 25,000/mm3. A bone marrow aspiration shows numerous immature cells that stain positive for CD10, CD19, and terminal deoxynucleotidyl transferase (TdT). Which of the following translocations is associated with a favorable prognosis for this patient's condition?
A. t(15;17)
B. t(14;18)
C. t(12;21) (Correct Answer)
D. t(8;14)
E. t(9;22)
Explanation: ***t(12;21)***
- The clinical presentation with **fatigue, irritability, leg pain, pallor, petechiae, lymphadenopathy**, and laboratory findings of **anemia, high leukocyte count, and thrombocytopenia** in a 5-year-old child are highly suggestive of **acute lymphoblastic leukemia (ALL)**. The presence of **CD10, CD19, and TdT positive immature cells** on bone marrow aspiration confirms the diagnosis of **B-cell ALL**.
- The **t(12;21) translocation** is one of the most common cytogenetic abnormalities found in childhood B-cell ALL and is typically associated with a **favorable prognosis** and higher rates of remission, particularly in children.
*t(15;17)*
- This translocation is characteristic of **acute promyelocytic leukemia (APML)**, a subtype of **acute myeloid leukemia (AML)**.
- APML presents with distinct features, including a high risk of **disseminated intravascular coagulation (DIC)**, and is treated with **all-trans retinoic acid (ATRA)**, which does not align with the patient's presentation of ALL.
*t(14;18)*
- This translocation is typically associated with **follicular lymphoma**, a type of **non-Hodgkin lymphoma** that primarily affects adults.
- Follicular lymphoma is a **B-cell malignancy** but presents as a solid tumor of lymphoid tissue rather than a widespread leukemia.
*t(8;14)*
- This translocation is the hallmark of **Burkitt's lymphoma**, another type of **B-cell non-Hodgkin lymphoma**.
- Burkitt's lymphoma is characterized by rapid tumor growth and often presents with an **extranodal mass**, such as in the jaw or abdomen, and is not typically associated with the widespread bone marrow involvement characteristic of ALL.
*t(9;22)*
- The **t(9;22) translocation**, known as the **Philadelphia chromosome**, is characteristic of **chronic myeloid leukemia (CML)** or, less commonly, a subset of ALL with a **poor prognosis**.
- While it can be seen in ALL, its presence generally indicates a **worse prognosis** and necessitates different treatment approaches, contrasting with the favorable outlook of t(12;21).
Question 146: A 10-month-old boy is admitted to the pediatric intensive care ward because of progressive dyspnea and fever. For the past 2 weeks, he was unsuccessfully treated for an upper respiratory tract infection with ampicillin. He has a history of neonatal sepsis, frequent respiratory tract infections since the age of 3 months, and recurrent otitis media. He was born full-term vaginally to a consanguineous couple from an uncomplicated pregnancy. He received routine immunizations until 6 months of age. The patient’s vital signs are as follows: blood pressure is 70/40 mm Hg, heart rate is 138/min, respiratory rate is 39/min, and temperature is 39.5℃ (103.1 ℉). Physical examination reveals cyanosis, nasal flare, intercostal retractions, and bilaterally decreased breath sounds with crackles heard over the lower lobes on auscultation. The chest X-ray confirms bilateral lower lobe pneumonia. The blood count shows the following findings:
Erythrocytes 4.1 x 106/mm3
Hgb 13 g/dL
Total leukocyte count 41,100/mm3
Neutrophils 74%
Lymphocytes 14%
Eosinophils 2%
Monocytes 10%
Basophils 0%
Platelet count 210,000/mm3
The patient is diagnosed with bilateral community-acquired lower lobe pneumonia and prescribed antibiotics. An immunological workup is performed to assess the patient’s immunity:
Measurement Result Normal range
Antibodies
Total serum IgG 22.0 mg/dL 231–1,411 mg/dL
Serum IgA 59.3 mg/dL 0–83 mg/dL
Serum IgM 111.9 mg/dL 0–145 mg/dL
Lymphocyte flow cytometry
CD3+ cells 2.2% 60–85%
CD19+ cells 95.1% 8–20%
CD16/CD56+ cells 0.1% 3–30%
Which of the following procedures is the option of choice for the further management of this patient?
A. Thymectomy
B. Periodical prophylactic antibiotic administration
C. Chemotherapy
D. Periodical intravenous immune globulin administration
E. Bone marrow transplantation (Correct Answer)
Explanation: ***Bone marrow transplantation***
- The patient's presentation with **recurrent severe infections** (neonatal sepsis, frequent respiratory infections, otitis media), **consanguinity**, and particularly the immunological findings (**severely low CD3+ cells (T-cells)** and **IgG**) are highly suggestive of **Severe Combined Immunodeficiency (SCID)**.
- **Bone marrow transplantation** is the only curative treatment for SCID, as it replaces the defective hematopoietic stem cells with healthy ones, allowing for the development of a functional immune system.
*Thymectomy*
- Thymectomy is the surgical removal of the thymus and is indicated in conditions like **myasthenia gravis** or **thymoma**.
- It would not treat an underlying immunodeficiency, and in a patient with SCID, the thymus is often already atrophic or dysfunctional, so its removal would not be beneficial.
*Periodical prophylactic antibiotic administration*
- While prophylactic antibiotics are used to prevent infections in immunocompromised patients, they are **palliative** and **not curative** for SCID.
- They would help manage symptoms but do not address the fundamental defect in immune cell development, leaving the patient vulnerable to severe and opportunistic infections.
*Chemotherapy*
- Chemotherapy is primarily used for treating **cancers** and certain **autoimmune conditions** due to its immunosuppressive effects.
- It is not indicated as a primary treatment for SCID unless it is part of a conditioning regimen for bone marrow transplantation to ablate the recipient's immune system.
*Periodical intravenous immune globulin administration*
- **IVIG** provides **passive immunity** by supplying exogenous antibodies, which can temporarily compensate for **antibody deficiencies** (like agammaglobulinemia).
- However, IVIG does not correct the severe **T-cell deficiency** that is characteristic of SCID, which is crucial for cell-mediated immunity and proper B-cell function; therefore, it is not curative for SCID alone.
Question 147: A 6-year-old girl is brought to the physician because of a 4-day history of irritation and redness in both eyes. Her symptoms initially started in the left eye and progressed to involve both eyes within 24 hours. She presents with profuse tearing and reports that her eyes are sticky and difficult to open in the morning. She was diagnosed with asthma 2 years ago and has been admitted to the hospital for acute exacerbations 3 times since then. Current medications include inhaled beclomethasone, inhaled albuterol, and montelukast. Her temperature is 38.2 °C (100.8°F). Physical examination reveals a tender left preauricular lymph node. There is chemosis and diffuse erythema of the bulbar conjunctiva bilaterally. Slit lamp examination reveals a follicular reaction in both palpebral conjunctivae and diffuse, fine epithelial keratitis of both corneas. Corneal sensation is normal. Which of the following is the most appropriate next step in management?
A. Topical erythromycin
B. Topical natamycin
C. Oral cetirizine
D. Topical prednisolone acetate
E. Supportive therapy (Correct Answer)
Explanation: ***Supportive therapy***
- The patient's symptoms, including **profuse tearing**, **follicular conjunctivitis**, and an **enlarged preauricular lymph node**, are highly suggestive of **viral conjunctivitis**, which is typically self-limiting.
- **Supportive measures** such as cool compresses and artificial tears are usually sufficient to manage discomfort and promote recovery.
*Topical erythromycin*
- **Topical erythromycin** is an **antibiotic** and would be appropriate for **bacterial conjunctivitis**, which typically presents with purulent discharge and less tearing.
- The clinical presentation with **follicular reaction** and **preauricular lymphadenopathy** is not typical of bacterial infection.
*Topical natamycin*
- **Topical natamycin** is an **antifungal agent** used to treat **fungal keratitis**, which is usually associated with a history of ocular trauma involving plant material or contact lens use in immunocompromised individuals.
- The patient's symptoms do not align with fungal infection, and there is no history to suggest this diagnosis.
*Oral cetirizine*
- **Oral cetirizine** is an **antihistamine** used to treat **allergic conjunctivitis**, which typically presents with itching, watery discharge, and often a history of seasonal allergies.
- While the patient has asthma, her current symptoms of an infectious nature (fever, follicular reaction, lymphadenopathy) make allergic conjunctivitis less likely.
*Topical prednisolone acetate*
- **Topical prednisolone acetate** is a **corticosteroid** that could reduce inflammation, but it is **contraindicated in viral conjunctivitis** as it can prolong viral shedding and potentially worsen the infection, leading to corneal ulceration or glaucoma.
- Corticosteroids should only be used after ruling out active viral infection, especially herpes simplex virus.
Question 148: A 2-year-old boy is brought to the physician by his mother for evaluation of recurrent infections and easy bruising. He has been hospitalized 3 times for severe skin and respiratory infections, which responded to treatment with antibiotics. Examination shows sparse silvery hair. The skin is hypopigmented and there are diffuse petechiae. Laboratory studies show a hemoglobin concentration of 8 g/dL, leukocyte count of 3000/mm3, and platelet count of 45,000/mm3. A peripheral blood smear shows giant cytoplasmic granules in granulocytes and platelets. Which of the following is the most likely underlying cause of this patient's symptoms?
A. Defective tyrosine kinase gene
B. WAS gene mutation
C. Defective NADPH oxidase
D. Defective lysosomal trafficking regulator gene (Correct Answer)
E. Defective CD40 ligand
Explanation: ***Defective lysosomal trafficking regulator gene***
- This clinical presentation including **recurrent infections**, **easy bruising (thrombocytopenia)**, **sparse silvery hair**, **hypopigmented skin**, and **giant cytoplasmic granules in granulocytes and platelets** is characteristic of **Chediak-Higashi syndrome**.
- **Chediak-Higashi syndrome** is an **autosomal recessive disorder** caused by a mutation in the **LYST (lysosomal trafficking regulator)** gene, leading to defective lysosomal function and formation of giant granules.
*Defective tyrosine kinase gene*
- A defective tyrosine kinase gene (such as **BTK**) is associated with **X-linked agammaglobulinemia (Bruton's agammaglobulinemia)**, which features recurrent bacterial infections due to absent B cells and immunoglobulins.
- It does not typically present with **oculocutaneous albinism**, **bleeding diathesis**, or **giant granules** in white blood cells.
*WAS gene mutation*
- A **WAS gene mutation** causes **Wiskott-Aldrich syndrome**, an **X-linked recessive disorder** characterized by the triad of **thrombocytopenia with small platelets**, **eczema**, and **recurrent infections**.
- While it involves recurrent infections and easy bruising, it does not include **silvery hair**, **hypopigmentation**, or **giant cytoplasmic granules**.
*Defective NADPH oxidase*
- A defective **NADPH oxidase** causes **Chronic Granulomatous Disease (CGD)**, characterized by **recurrent severe bacterial and fungal infections** due to impaired phagocyte oxidative burst.
- CGD is not associated with **silvery hair**, **hypopigmentation**, **thrombocytopenia**, or the presence of **giant cytoplasmic granules**.
*Defective CD40 ligand*
- A defective **CD40 ligand** on T cells causes **Hyper-IgM syndrome**, an **X-linked immunodeficiency** characterized by normal or elevated IgM levels but low levels of IgG, IgA, and IgE, leading to recurrent infections.
- It does not present with **silvery hair**, **hypopigmentation**, or the characteristic **hematologic abnormalities** seen in this patient.
Question 149: A 9-year-old boy is brought to the emergency department for the evaluation of diarrhea and vomiting for the last 2 days. During this period, he has had about 12 watery, non-bloody bowel movements and has vomited three times. He came back from a trip to India 3 days ago, where he and his family were visiting relatives. He has not been able to eat anything since the symptoms started. The patient has not urinated since yesterday. He appears pale. His temperature is 38°C (100.4°F), pulse is 106/min, and blood pressure is 96/60 mm Hg. Examination shows dry mucous membranes. The abdomen is soft with no organomegaly. Bowel sounds are hyperactive. Laboratory studies show:
Hemoglobin 13 g/dL
Serum
Na+ 148 mEq/L
Cl- 103 mEq/L
K+ 3.7 mEq/L
HCO3- 19 mEq/L
Urea nitrogen 80 mg/dL
Glucose 90 mg/dL
Creatinine 2 mg/dL
Intravenous fluid resuscitation is begun. Which of the following is the most likely cause of this patient's abnormal renal laboratory findings?
A. Urinary tract obstruction
B. IgA complex deposition
C. Decreased renal perfusion (Correct Answer)
D. Renal artery stenosis
E. Glomerulonephritis
Explanation: ***Decreased renal perfusion***
- The patient's presentation with **diarrhea and vomiting, dry mucous membranes**, **hypotension (96/60 mm Hg)**, **tachycardia (106/min)**, and **oliguria** (no urination since yesterday) indicates significant **volume depletion** and **dehydration**.
- This leads to **decreased blood flow to the kidneys (prerenal azotemia)**, resulting in **elevated BUN (80 mg/dL) and creatinine (2 mg/dL)**, along with a **high BUN/creatinine ratio** (40:1).
*Urinary tract obstruction*
- While it can cause elevated BUN and creatinine, it typically presents with **suprapubic pain, difficulty voiding**, or a **palpable bladder**, none of which are described.
- Obstruction does not explain the widespread signs of **dehydration** and **hypoperfusion**.
*IgA complex deposition*
- This refers to **IgA nephropathy**, a form of **glomerulonephritis**, which typically causes **hematuria** rather than primarily acute kidney injury from dehydration.
- The clinical picture of acute fluid loss and hypovolemia does not align with the typical presentation of IgA nephropathy.
*Renal artery stenosis*
- This condition involves **narrowing of the renal arteries**, leading to **chronic kidney disease** and often **hypertension**, which is contrary to the patient's **hypotension**.
- It does not present as an acute syndrome linked to a recent diarrheal illness and systemic dehydration.
*Glomerulonephritis*
- Glomerulonephritis usually presents with **hematuria, proteinuria, edema**, and **hypertension**, none of which are prominent features here.
- While it can cause elevated BUN and creatinine, the primary cause of renal dysfunction in this patient is clearly related to **volume depletion** from gastrointestinal losses.
Question 150: A 13-month-old boy with sickle cell anemia is brought to the emergency department because of continuous crying and severe left-hand swelling. His condition started 2 hours earlier without any preceding trauma. The child was given diclofenac syrup at home with no relief. The temperature is 37°C (98.6°F), blood pressure is 100/60 mm Hg, and pulse is 100/min. The physical examination reveals swelling and tenderness to palpation of the left hand. The hemoglobin level is 10.4 g/dL. Which of the following is the best initial step in management of this patient condition?
A. Magnetic resonance imaging (MRI) of the affected joint
B. Incentive spirometry
C. Joint aspiration
D. Intravenous meperidine
E. Intravenous morphine (Correct Answer)
Explanation: ***Intravenous morphine***
- The patient presents with classic signs of **dactylitis**, a painful vaso-occlusive crisis in sickle cell anemia, characterized by acute onset of **painful swelling of hands and feet**.
- **Opioids** like intravenous morphine are the cornerstone for managing severe pain in sickle cell pain crises, and a **multimodal approach** to pain control is recommended.
*Magnetic resonance imaging (MRI) of the affected joint*
- While MRI can visualize soft tissue and bone, it is **not the initial step** in managing a sickle cell pain crisis due to its cost, time, and potential need for sedation in a child.
- The diagnosis of **dactylitis is primarily clinical**, based on the patient's history and physical examination.
*Incentive spirometry*
- **Incentive spirometry** is primarily used to prevent or treat **pulmonary complications** like atelectasis, often in postoperative patients or those with acute chest syndrome.
- It is not indicated for the management of **acute pain due to dactylitis** and would not address the patient's immediate problem.
*Joint aspiration*
- **Joint aspiration** is performed to diagnose infectious arthritis or to relieve pressure from effusions, which presents with signs of inflammation.
- The patient's symptoms are consistent with **vaso-occlusive crisis** in sickle cell disease, not an infection, making aspiration unnecessary and potentially harmful.
*Intravenous meperidine*
- **Meperidine (Demerol)** is generally **avoided in sickle cell patients** due to the accumulation of its metabolite, **normeperidine**, which can cause **neurotoxicity**, including seizures.
- Other opioids like morphine or hydromorphone are preferred for severe pain in this population.
