A 4-year-old boy is brought to the emergency department because of fever, nausea, and headache for 1 day. His temperature is 39.7°C (103.5°F). Examination shows involuntary flexion of the knees and hips when the neck is flexed. A lumbar puncture is performed and cerebrospinal fluid (CSF) analysis shows numerous segmented neutrophils and a decreased glucose concentration. Gram stain of the CSF shows gram-negative diplococci. This patient is at increased risk for which of the following complications?
Q22
A 6-year-old male is brought to the pediatrician by his mother because she is concerned about his breathing. She states that every once in a while he seems to have bouts of coughing but doesn't have any significant difficulty breathing. She demands that the pediatrician begin treatment with albuterol as she is convinced that her child has asthma. The pediatrician, not fully convinced, states that he will run a test that will help to rule out asthma as a diagnosis. To which of the following tests is the pediatrician referring?
Q23
A 3-year-old boy is brought to the emergency department by his mother for abdominal pain. She states that he has refused to eat and keeps clutching his stomach saying “ow.” She reports that he has not had any vomiting or diarrhea. She says that he has not had a bowel movement in 3 days. The family recently moved from Namibia and has not established care. He has no known medical conditions and takes no medications. The mother says there is a family history of a “blood illness.” On physical examination, there is mild distension with tenderness in the bilateral lower quadrants without organomegaly. An ultrasound of the abdomen reveals 2 gallstones without gallbladder wall thickening or ductal dilation and a negative Murphy sign. An abdominal radiograph shows moderate stool burden in the large bowel and rectum. Labs are obtained, as below:
Hemoglobin: 9 g/dL
Platelet count: 300,000/mm^3
Mean corpuscular volume (MCV): 85 µm^3
Reticulocyte count: 5%
Lactate dehydrogenase (LDH): 532 U/L
Leukocyte count: 11/mm^3
Serum iron: 140 mcg/dL
Transferrin saturation: 31% (normal range 20-50%)
Total iron binding capacity (TIBC): 400 mcg/dL (normal range 240 to 450 mcg/dL)
A hemoglobin electrophoresis shows hemoglobin S, increased levels of hemoglobin F, and no hemoglobin A. The results are discussed with the patient’s mother including recommendations for increasing fiber in the patient’s diet and starting hydroxyurea. Which of the following should also be part of management for the patient’s condition?
Q24
A 2-year-old girl is brought to the emergency department because of bilateral hand pain and swelling. Her parents say the pain began 1 week ago and has gotten progressively worse. Two weeks ago, the patient had a low-grade fever and lace-like rash on her arms and trunk for several days. The patient appears to be in distress. Her temperature is 38.5°C (101.4°F), pulse is 130/min, and respirations are 25/min. The dorsum of her hands and fingers are erythematous, swollen, warm, and tender to palpation. Her hemoglobin concentration is 9.1 g/dL and leukocyte count is 8,000/mm3. A peripheral blood smear is shown. Which of the following interventions is most appropriate to prevent a recurrence of this patient's symptoms?
Q25
A 5-year-old boy with a history of severe allergies and recurrent sinusitis presents with foul-smelling, fatty diarrhea. He is at the 50th percentile for height and weight. The boy's mother reports that he has had several such episodes of diarrhea over the years. He does not have any known history of fungal infections or severe viral infections. Which of the following is the most likely underlying cause of this boy's presentation?
Q26
A 4-year-old boy presents to the emergency department after his parents found him drinking blue liquid out of an unlabeled bottle in the garage. They have no idea what was in the bottle and are concerned for his health. They have brought the bottle with them to the emergency department. The child's past medical history is not remarkable, and he is currently not taking any medications. The patient's vitals are within normal limits for his age. Physical exam reveals a crying child who is drooling. A radiograph is performed, and the child's vitals are closely monitored. It is determined that the blue liquid is a strong alkali. Which of the following is the best next step in management?
Q27
A 3-year-old boy presents with fever, generalized fatigue, nausea, and progressive anemia. The patient’s mother says his condition was normal until one week ago when he started having flu-like symptoms such as fever, general fatigue, and abdominal discomfort. Past medical experience is significant for sickle cell disease, diagnosed 2 years ago. His vital signs include: blood pressure 98/50 mm Hg, pulse 120/min, temperature 39.0℃ (102.0℉). On physical examination, the patient is crying excessively and his skin and the conjunctivae look pale. Splenomegaly is noted. There is no skin rash nor lymphadenopathy. Laboratory findings are significant for the following:
Total WBC count 22,000/mm3
Neutrophils 35%
Lymphocytes 44%
Atypical lymphocytes 9%
Monocytes 12%
RBC 1. 6 million/mm3
Hb 5.4 g/dL
Hct 14.4%
MCV 86 fL
MCHC 37.5%
Reticulocytes 0.1%
A peripheral blood smear shows sickle cells. A direct and indirect Coombs test is negative. Which of the following is the most likely cause of this patient’s most recent symptoms?
Q28
A 7-year-old girl is brought to the physician because of generalized fatigue and dark urine for 1 week. Four weeks ago, she was treated with topical mupirocin for a skin infection. Her 5-year-old brother has steroid-resistant nephrotic syndrome. Her temperature is 37°C (98.6°F), pulse is 90/min, respirations are 14/min, and blood pressure is 132/89 mm Hg. Examination shows periorbital and 1+ pretibial edema bilaterally. The remainder of the examination shows no abnormalities. Laboratory studies show:
Hemoglobin 12.9 g/dL
Leukocyte count 7,200/mm3
Platelet count 230,000/mm3
Serum
Urea nitrogen 32 mg/dL
Creatinine 1.8 mg/dL
Urine
Blood 2+
Protein 2+
Glucose negative
RBC 12–14/hpf with dysmorphic features
RBC casts numerous
Which of the following is the most likely cause of these findings?
Q29
A 3-month-old boy presents to his pediatrician with persistent diarrhea, oral candidiasis, and signs and symptoms of respiratory syncytial virus (RSV) pneumonia. He is very lean with weight in the 10th percentile. His blood pressure is 105/64 mm Hg and heart rate is 84/min. He is being evaluated for an immunodeficiency. Laboratory results for HIV are negative by polymerase chain reaction (PCR). Which of the following is the most likely cause of this child’s presentation?
Q30
A 7-year-old boy is brought to the emergency room because of severe, acute diarrhea. He is drowsy with a dull, lethargic appearance. He has sunken eyes, poor skin turgor, and dry oral mucous membranes and tongue. He has a rapid, thready pulse with a systolic blood pressure of 60 mm Hg and his respirations are 33/min. His capillary refill time is 6 sec. He has had no urine output for the past 24 hours. Which of the following is the most appropriate next step in treatment?
Infectious Disease US Medical PG Practice Questions and MCQs
Question 21: A 4-year-old boy is brought to the emergency department because of fever, nausea, and headache for 1 day. His temperature is 39.7°C (103.5°F). Examination shows involuntary flexion of the knees and hips when the neck is flexed. A lumbar puncture is performed and cerebrospinal fluid (CSF) analysis shows numerous segmented neutrophils and a decreased glucose concentration. Gram stain of the CSF shows gram-negative diplococci. This patient is at increased risk for which of the following complications?
A. Acute pancreatitis
B. Deep neck abscess
C. Temporal lobe inflammation
D. Vesicular skin rash
E. Adrenal insufficiency (Correct Answer)
Explanation: ***Adrenal insufficiency***
- The patient presents with **bacterial meningitis**, evidenced by fever, nuchal rigidity (**Brudzinski's sign**), turbid CSF with **neutrophils**, **decreased glucose**, and **gram-negative diplococci** (likely *Neisseria meningitidis*).
- Severe meningococcal infection can lead to **Waterhouse-Friderichsen syndrome**, characterized by **adrenal hemorrhage** and subsequent acute adrenal insufficiency.
*Acute pancreatitis*
- **Pancreatitis** is not a typical complication of bacterial meningitis or meningococcal disease.
- While some severe infections can cause systemic inflammation, direct pancreatic involvement is rare.
*Deep neck abscess*
- A **deep neck abscess** results from localized infection in the deep spaces of the neck, often polymicrobial.
- It is not a direct complication of meningococcal meningitis; the infection is primarily within the central nervous system.
*Temporal lobe inflammation*
- **Temporal lobe inflammation** (encephalitis) is more commonly associated with **viral infections** like **Herpes Simplex Virus (HSV)**.
- While meningitis can cause diffuse brain inflammation, specifically targeting the temporal lobe is less characteristic of bacterial meningitis.
*Vesicular skin rash*
- A **vesicular rash** is characteristic of **viral infections**, such as **chickenpox** (varicella-zoster virus) or herpes simplex virus.
- Meningococcal disease typically presents with a **petechial or purpuric rash**, not a vesicular rash.
Question 22: A 6-year-old male is brought to the pediatrician by his mother because she is concerned about his breathing. She states that every once in a while he seems to have bouts of coughing but doesn't have any significant difficulty breathing. She demands that the pediatrician begin treatment with albuterol as she is convinced that her child has asthma. The pediatrician, not fully convinced, states that he will run a test that will help to rule out asthma as a diagnosis. To which of the following tests is the pediatrician referring?
A. Methacholine challenge test (Correct Answer)
B. Pulmonary function tests
C. Allergy testing
D. CT scan
E. Chest radiograph
Explanation: ***Methacholine challenge test***
- A negative **methacholine challenge test** effectively rules out **asthma** by demonstrating the absence of **airway hyperresponsiveness**.
- This test involves inhaling increasing doses of **methacholine**, a **bronchoconstrictor**, to assess the degree of airway narrowing.
*Pulmonary function tests*
- While **pulmonary function tests (PFTs)** like **spirometry** can aid in diagnosing asthma, they primarily measure baseline lung function and reversibility rather than ruling out the disease when results are normal between exacerbations.
- PFTs might be normal in a child with intermittent symptoms or mild asthma, making them less definitive for ruling out the condition as compared to a methacholine challenge.
*Allergy testing*
- **Allergy testing** can identify specific allergens that might trigger asthma, but a positive result does not confirm asthma nor does a negative result definitively rule it out.
- Many people have allergies without having asthma, and some asthmatics do not have allergic triggers.
*CT scan*
- A **CT scan** of the chest is typically used to rule out other lung diseases or anatomical abnormalities, such as **bronchiectasis** or **foreign body aspiration**, but it is not a primary diagnostic tool for asthma.
- It would not show the dynamic airway hyperresponsiveness characteristic of asthma.
*Chest radiograph*
- A **chest radiograph** is usually normal in asthma and is primarily used to rule out other causes of cough or respiratory symptoms, such as **pneumonia** or **atelectasis**.
- It cannot assess airway hyperresponsiveness or confirm/rule out asthma itself.
Question 23: A 3-year-old boy is brought to the emergency department by his mother for abdominal pain. She states that he has refused to eat and keeps clutching his stomach saying “ow.” She reports that he has not had any vomiting or diarrhea. She says that he has not had a bowel movement in 3 days. The family recently moved from Namibia and has not established care. He has no known medical conditions and takes no medications. The mother says there is a family history of a “blood illness.” On physical examination, there is mild distension with tenderness in the bilateral lower quadrants without organomegaly. An ultrasound of the abdomen reveals 2 gallstones without gallbladder wall thickening or ductal dilation and a negative Murphy sign. An abdominal radiograph shows moderate stool burden in the large bowel and rectum. Labs are obtained, as below:
Hemoglobin: 9 g/dL
Platelet count: 300,000/mm^3
Mean corpuscular volume (MCV): 85 µm^3
Reticulocyte count: 5%
Lactate dehydrogenase (LDH): 532 U/L
Leukocyte count: 11/mm^3
Serum iron: 140 mcg/dL
Transferrin saturation: 31% (normal range 20-50%)
Total iron binding capacity (TIBC): 400 mcg/dL (normal range 240 to 450 mcg/dL)
A hemoglobin electrophoresis shows hemoglobin S, increased levels of hemoglobin F, and no hemoglobin A. The results are discussed with the patient’s mother including recommendations for increasing fiber in the patient’s diet and starting hydroxyurea. Which of the following should also be part of management for the patient’s condition?
A. Vaccination for parvovirus
B. Iron supplementation
C. Folate supplementation
D. Ursodeoxycholic acid
E. Penicillin until age 5 (Correct Answer)
Explanation: ***Penicillin until age 5***
- The patient has **sickle cell anemia** (Hb SS genotype, indicated by Hb S, increased Hb F, and absent Hb A), making them highly susceptible to **encapsulated bacterial infections**, particularly *Streptococcus pneumoniae*.
- **Prophylactic penicillin** until at least age 5 (and often longer) is crucial to prevent life-threatening infections like **sepsis** and **meningitis** due to functional asplenia.
- This is the **most critical missing intervention** for this newly diagnosed patient.
*Vaccination for parvovirus*
- While **parvovirus B19 infection** can cause **aplastic crisis** in sickle cell patients, there is **no vaccine available** for parvovirus.
- Management for parvovirus exposure or infection in sickle cell patients is typically supportive, including **transfusions** if severe aplastic crisis occurs.
*Iron supplementation*
- Patients with sickle cell anemia often have **iron overload** due to frequent transfusions and increased red blood cell turnover, not iron deficiency.
- Iron studies (normal serum iron, TIBC, transferrin saturation) in this patient do not suggest iron deficiency, and iron supplementation could be **harmful**.
*Folate supplementation*
- **Folate supplementation** (typically 1 mg daily) is indeed part of **standard long-term management** for sickle cell disease due to increased folate requirements from chronic hemolysis and rapid RBC turnover.
- However, in this clinical scenario asking what "should ALSO be part of management" for a newly diagnosed patient, **penicillin prophylaxis takes priority** as it prevents immediate life-threatening infections, whereas folate addresses chronic hematologic needs that are less urgently critical.
*Ursodeoxycholic acid*
- **Ursodeoxycholic acid** is used to manage gallstones, particularly to dissolve small cholesterol stones, but is ineffective for **pigment stones** (composed of bilirubin from chronic hemolysis) that are typical in sickle cell disease.
- Management of symptomatic gallstones in SCD usually involves **cholecystectomy** rather than medical dissolution therapy.
Question 24: A 2-year-old girl is brought to the emergency department because of bilateral hand pain and swelling. Her parents say the pain began 1 week ago and has gotten progressively worse. Two weeks ago, the patient had a low-grade fever and lace-like rash on her arms and trunk for several days. The patient appears to be in distress. Her temperature is 38.5°C (101.4°F), pulse is 130/min, and respirations are 25/min. The dorsum of her hands and fingers are erythematous, swollen, warm, and tender to palpation. Her hemoglobin concentration is 9.1 g/dL and leukocyte count is 8,000/mm3. A peripheral blood smear is shown. Which of the following interventions is most appropriate to prevent a recurrence of this patient's symptoms?
A. Blood transfusions
B. Regular red cell exchange transfusions
C. Prophylactic penicillin
D. Hydroxyurea (Correct Answer)
E. IV cefazolin
Explanation: ***Hydroxyurea***
- The patient's presentation with **bilateral hand pain and swelling (dactylitis)**, **anemia**, and a prior history of **fever and a rash (parvovirus B19 infection triggering a crisis)**, along with the peripheral blood smear showing **sickled red blood cells**, is highly suggestive of **sickle cell disease**.
- **Hydroxyurea** is the most appropriate long-term intervention to reduce the frequency and severity of **vaso-occlusive crises**, including dactylitis, acute chest syndrome, and the need for transfusions, by increasing **fetal hemoglobin (HbF)** production.
*Blood transfusions*
- **Blood transfusions** are used for acute management of severe anemia or complications like **acute chest syndrome** or **stroke** in sickle cell disease.
- They do not prevent the recurrence of symptoms in the long term but rather address acute exacerbations.
*Regular red cell exchange transfusions*
- **Regular red cell exchange transfusions** are primarily indicated for patients with a history of **stroke** or those at high risk for stroke, aiming to reduce the percentage of **sickle hemoglobin (HbS)**.
- While effective in preventing certain complications, they are not the first-line prophylactic treatment for preventing general vaso-occlusive crises or dactylitis in a 2-year-old without a history of stroke.
*Prophylactic penicillin*
- **Prophylactic penicillin** is critical for preventing **pneumococcal sepsis** in children with sickle cell disease due to functional asplenia.
- While important for overall management, it does not prevent vaso-occlusive crises like dactylitis, which is the primary concern here.
*IV cefazolin*
- **IV cefazolin** is an antibiotic used to treat bacterial infections, particularly those caused by **gram-positive bacteria**.
- There is no indication for acute bacterial infection requiring intravenous antibiotics, and it has no role in preventing the recurrence of vaso-occlusive crises in sickle cell disease.
Question 25: A 5-year-old boy with a history of severe allergies and recurrent sinusitis presents with foul-smelling, fatty diarrhea. He is at the 50th percentile for height and weight. The boy's mother reports that he has had several such episodes of diarrhea over the years. He does not have any known history of fungal infections or severe viral infections. Which of the following is the most likely underlying cause of this boy's presentation?
A. IgA deficiency (Correct Answer)
B. Hyper IgE syndrome
C. Thymic aplasia
D. Severe combined immune deficiency
E. Wiskott-Aldrich Syndrome
Explanation: ***IgA deficiency***
- **Selective IgA deficiency** is the most common primary immunodeficiency and is often associated with recurrent **sinopulmonary infections** and **gastrointestinal issues** like malabsorption, leading to fatty, foul-smelling stools.
- While patients can have allergies, the key here is the combination of recurrent sinopulmonary symptoms (sinusitis) and malabsorption in a child who is otherwise growing well and lacks severe opportunistic infections.
*Hyper IgE syndrome*
- Characterized by recurrent **staphylococcal infections**, coarse facial features, and markedly elevated IgE levels, which are not mentioned here.
- While patients can have allergies and recurrent infections, the specific presentation of fatty diarrhea and lack of severe staph infections makes this less likely.
*Thymic aplasia*
- Also known as **DiGeorge syndrome**, it primarily causes **T-cell deficiency**, leading to recurrent viral and fungal infections, cardiac defects, and hypocalcemia.
- The patient's history does not include severe viral or fungal infections, and he is growing well, making severe T-cell dysfunction unlikely.
*Severe combined immune deficiency*
- SCID causes profound defects in both **T-cell and B-cell immunity**, leading to severe, life-threatening infections early in infancy, **failure to thrive**, and opportunistic infections.
- This child's relatively good growth (50th percentile for height and weight) and lack of severe, early opportunistic infections make SCID highly unlikely.
*Wiskott-Aldrich Syndrome*
- Characterized by the triad of **thrombocytopenia** with small platelets, **eczema**, and recurrent infections.
- The patient's presentation does not include bleeding tendencies or eczema, which are hallmark features of Wiskott-Aldrich Syndrome.
Question 26: A 4-year-old boy presents to the emergency department after his parents found him drinking blue liquid out of an unlabeled bottle in the garage. They have no idea what was in the bottle and are concerned for his health. They have brought the bottle with them to the emergency department. The child's past medical history is not remarkable, and he is currently not taking any medications. The patient's vitals are within normal limits for his age. Physical exam reveals a crying child who is drooling. A radiograph is performed, and the child's vitals are closely monitored. It is determined that the blue liquid is a strong alkali. Which of the following is the best next step in management?
A. Administration of a diluent
B. Gastrografin swallow and endoscopy (Correct Answer)
C. Administration of a weak acid
D. Charcoal
E. Ipecac
Explanation: ***Gastrografin swallow and endoscopy***
- **Endoscopy within 12-24 hours** is the gold standard for evaluating caustic ingestions, allowing direct visualization of mucosal injury and grading of severity to guide management.
- A **Gastrografin swallow** (water-soluble contrast study) may be considered if esophageal perforation is suspected, though it is not routinely performed in all cases; CT imaging is often preferred for perforation assessment.
- The key intervention is **endoscopy**, which should not be delayed beyond 24 hours to avoid missing the optimal window for assessment before granulation tissue forms.
*Administration of a diluent*
- Administering a diluent is **contraindicated** when there are signs of esophageal injury such as drooling, as it can worsen inflammation, induce vomiting, or lead to perforation.
- Dilution may also cause vomiting which re-exposes the esophagus to the caustic substance, causing additional injury.
*Administration of a weak acid*
- Neutralizing a strong alkali with a weak acid is **not recommended** due to the exothermic reaction this causes, generating heat and worsening tissue damage.
- The precise amount of acid needed for safe neutralization cannot be reliably determined, making this approach dangerous.
*Charcoal*
- **Activated charcoal** does not bind to strong alkalis or acids and is therefore not indicated for caustic ingestions.
- It may also impede endoscopic visualization, delaying definitive diagnosis and management.
*Ipecac*
- **Syrup of ipecac** induces vomiting and is **contraindicated** in caustic ingestions because it causes re-exposure of the esophagus to the corrosive substance, increasing mucosal damage.
- Vomiting also carries significant risk of aspiration into the lungs, which can cause severe respiratory complications.
Question 27: A 3-year-old boy presents with fever, generalized fatigue, nausea, and progressive anemia. The patient’s mother says his condition was normal until one week ago when he started having flu-like symptoms such as fever, general fatigue, and abdominal discomfort. Past medical experience is significant for sickle cell disease, diagnosed 2 years ago. His vital signs include: blood pressure 98/50 mm Hg, pulse 120/min, temperature 39.0℃ (102.0℉). On physical examination, the patient is crying excessively and his skin and the conjunctivae look pale. Splenomegaly is noted. There is no skin rash nor lymphadenopathy. Laboratory findings are significant for the following:
Total WBC count 22,000/mm3
Neutrophils 35%
Lymphocytes 44%
Atypical lymphocytes 9%
Monocytes 12%
RBC 1. 6 million/mm3
Hb 5.4 g/dL
Hct 14.4%
MCV 86 fL
MCHC 37.5%
Reticulocytes 0.1%
A peripheral blood smear shows sickle cells. A direct and indirect Coombs test is negative. Which of the following is the most likely cause of this patient’s most recent symptoms?
A. IgG-mediated hemolytic anemia
B. Parvovirus infection (Correct Answer)
C. Sickle cell disease
D. Fanconi’s anemia
E. Myelofibrosis
Explanation: ***Parvovirus infection***
- The patient's presentation with **acute onset of severe anemia** (Hb 5.4 g/dL) and **reticulocytopenia (0.1%)** in the context of sickle cell disease is highly suggestive of **aplastic crisis** triggered by Parvovirus B19.
- **Parvovirus B19** specifically targets and destroys **erythroid progenitor cells** in the bone marrow, leading to a temporary cessation of red blood cell production, especially critical in patients with underlying hemolytic conditions like sickle cell disease.
*IgG-mediated hemolytic anemia*
- This condition is characterized by **increased red blood cell destruction** due to antibodies, which would typically result in **elevated reticulocyte counts** as the bone marrow tries to compensate.
- The patient's **negative Coombs test** and extremely **low reticulocyte count (0.1%)** argue against an immune-mediated hemolytic process.
*Sickle cell disease*
- While the patient has sickle cell disease as his **underlying chronic condition**, this diagnosis alone does not explain his **acute presentation with reticulocytopenia**.
- A typical **sickle cell crisis** (vaso-occlusive or hemolytic) would present with pain and either normal or **elevated reticulocyte counts** (>2-3%) due to compensatory bone marrow response to ongoing hemolysis, not the profound **reticulocyte suppression (0.1%)** seen here.
- The key finding is that something has **acutely suppressed his bone marrow's erythroid production**, which is not a feature of uncomplicated sickle cell disease.
*Fanconi's anemia*
- **Fanconi's anemia** is a **congenital aplastic anemia** characterized by pancytopenia and often associated with physical abnormalities (e.g., thumb anomalies, short stature, cafe-au-lait spots).
- The acute, progressive nature of the symptoms over a week, coupled with his previous normal condition until recently, makes a newly presenting Fanconi's anemia less likely.
*Myelofibrosis*
- **Myelofibrosis** is a chronic myeloproliferative neoplasm characterized by **bone marrow fibrosis**, leading to ineffective hematopoiesis and often **extramedullary hematopoiesis** (causing splenomegaly).
- It typically presents as a **chronic, progressive disease** with teardrop cells on peripheral smear, and a more insidious onset, which does not align with the acute, flu-like prodrome and sudden severe anemia.
Question 28: A 7-year-old girl is brought to the physician because of generalized fatigue and dark urine for 1 week. Four weeks ago, she was treated with topical mupirocin for a skin infection. Her 5-year-old brother has steroid-resistant nephrotic syndrome. Her temperature is 37°C (98.6°F), pulse is 90/min, respirations are 14/min, and blood pressure is 132/89 mm Hg. Examination shows periorbital and 1+ pretibial edema bilaterally. The remainder of the examination shows no abnormalities. Laboratory studies show:
Hemoglobin 12.9 g/dL
Leukocyte count 7,200/mm3
Platelet count 230,000/mm3
Serum
Urea nitrogen 32 mg/dL
Creatinine 1.8 mg/dL
Urine
Blood 2+
Protein 2+
Glucose negative
RBC 12–14/hpf with dysmorphic features
RBC casts numerous
Which of the following is the most likely cause of these findings?
A. Antibodies against type IV collagen
B. Subepithelial immune complex deposition (Correct Answer)
C. Defective circulating IgA antibodies
D. Antibodies against cell nucleus proteins
E. Inflammation of small-sized blood vessels
Explanation: ***Subepithelial immune complex deposition***
- The history of a recent **skin infection** treated with mupirocin, followed by symptoms of **fatigue**, **dark urine**, **edema**, and **hypertension**, strongly suggests **post-streptococcal glomerulonephritis (PSGN)**.
- PSGN is characterized by the deposition of **immune complexes** (containing streptococcal antigens and antibodies) in the subepithelial space of the glomeruli, leading to inflammation and kidney injury.
*Antibodies against type IV collagen*
- This is characteristic of **Goodpasture syndrome**, which presents with rapidly progressive glomerulonephritis and often pulmonary hemorrhage.
- The patient's age and history of a preceding skin infection do not fit the typical presentation of Goodpasture syndrome, and there is no mention of hemoptysis.
*Defective circulating IgA antibodies*
- This describes **IgA nephropathy** (Berger's disease), which is typically characterized by recurrent episodes of gross hematuria, often triggered by a respiratory or gastrointestinal infection.
- While there is hematuria, the timing of symptoms (4 weeks after skin infection) and the presence of significant edema and hypertension differentiate it from typical IgA nephropathy.
*Antibodies against cell nucleus proteins*
- This is characteristic of **systemic lupus erythematosus (SLE)**, which can cause lupus nephritis.
- While lupus nephritis can present with proteinuria, hematuria, and renal failure, the patient's age (7 years old) and the clear history of a preceding streptococcal skin infection without other systemic lupus symptoms make PSGN a more likely diagnosis.
*Inflammation of small-sized blood vessels*
- This describes **vasculitis**, which can affect the kidney (e.g., ANCA-associated vasculitis).
- While vasculitis can cause glomerulonephritis, the specific clinical picture here, especially the recent skin infection and laboratory findings, points more directly to an immune complex-mediated process like PSGN rather than primary small vessel vasculitis.
Question 29: A 3-month-old boy presents to his pediatrician with persistent diarrhea, oral candidiasis, and signs and symptoms of respiratory syncytial virus (RSV) pneumonia. He is very lean with weight in the 10th percentile. His blood pressure is 105/64 mm Hg and heart rate is 84/min. He is being evaluated for an immunodeficiency. Laboratory results for HIV are negative by polymerase chain reaction (PCR). Which of the following is the most likely cause of this child’s presentation?
A. Grossly reduced levels of B cells
B. An X-linked inheritance of HLA genes
C. Selective IgA deficiency
D. Defective T cell function (Correct Answer)
E. Defective isotype switching
Explanation: ***Defective T cell function***
- The presentation with recurrent infections (oral candidiasis, RSV pneumonia), persistent diarrhea, and **failure to thrive (lean, 10th percentile weight)** in a young infant, despite negative HIV PCR, strongly suggests a **severe combined immunodeficiency (SCID)**.
- **T-cell dysfunction is the hallmark of SCID**, leading to a broad susceptibility to opportunistic pathogens and impaired immune responses.
*Grossly reduced levels of B cells*
- While some immunodeficiencies involve B-cell defects (e.g., **X-linked agammaglobulinemia**), the primary clinical picture here (severe viral and fungal infections, failure to thrive) points more strongly to a profound T-cell defect affecting both humoral and cellular immunity.
- Reduced B cells alone would primarily result in recurrent bacterial infections rather than the observed opportunistic infections.
*An X-linked inheritance of HLA genes*
- **HLA genes (Major Histocompatibility Complex)** are located on **chromosome 6**, not the X chromosome, and are crucial for antigen presentation, not typically associated with X-linked inheritance patterns.
- Defects in HLA (e.g., bare lymphocyte syndrome) can impair T-cell function but are not solely X-linked and would still fall under the umbrella of defective T-cell function.
*Selective IgA deficiency*
- Patients with selective IgA deficiency are often **asymptomatic** or experience **recurrent sinopulmonary and gastrointestinal infections** but typically do not present with severe opportunistic infections like RSV pneumonia and persistent candidiasis with failure to thrive.
- **T-cell function is preserved** in selective IgA deficiency, making the severe presentation less likely.
*Defective isotype switching*
- This primarily affects the ability of B cells to produce different classes of antibodies **(IgG, IgA, IgE)**, often due to defects in T follicular helper cells or B cell intrinsic defects.
- While it can lead to recurrent infections, particularly bacterial, it does not typically cause the severe, opportunistic infections and failure to thrive seen with primary T-cell defects like SCID.
Question 30: A 7-year-old boy is brought to the emergency room because of severe, acute diarrhea. He is drowsy with a dull, lethargic appearance. He has sunken eyes, poor skin turgor, and dry oral mucous membranes and tongue. He has a rapid, thready pulse with a systolic blood pressure of 60 mm Hg and his respirations are 33/min. His capillary refill time is 6 sec. He has had no urine output for the past 24 hours. Which of the following is the most appropriate next step in treatment?
A. Start IV fluid resuscitation by administering colloid solutions
B. Provide oral rehydration therapy to correct dehydration
C. Give initial IV bolus of 2 L of Ringer’s lactate, followed by packed red cells, fresh frozen plasma, and platelets in a ratio of 1:1:1
D. Start IV fluid resuscitation with normal saline or Ringer’s lactate, along with monitoring of vitals and urine output (Correct Answer)
E. Give antidiarrheal drugs
Explanation: ***Start IV fluid resuscitation with normal saline or Ringer's lactate, along with monitoring of vitals and urine output***
- This patient presents with **severe dehydration** and **hypovolemic shock** (lethargy, sunken eyes, poor skin turgor, dry mucous membranes, rapid thready pulse, hypotension [systolic BP 60 mmHg], tachypnea, prolonged capillary refill >5 seconds, and anuria).
- According to **PALS guidelines**, the immediate priority is rapid intravenous administration of **isotonic crystalloids** (normal saline or Ringer's lactate) given as **20 mL/kg boluses** over 5-20 minutes, repeated as needed based on clinical response.
- Close monitoring of vital signs, mental status, perfusion (capillary refill), and urine output is essential to assess response to resuscitation and guide further fluid management.
*Start IV fluid resuscitation by administering colloid solutions*
- While colloids (albumin, synthetic colloids) can expand intravascular volume, **isotonic crystalloids** are preferred for initial resuscitation in severe dehydration per **WHO and PALS guidelines**.
- Crystalloids are equally effective, more readily available, less expensive, and have fewer potential adverse effects compared to colloids in pediatric dehydration.
- There is no proven survival benefit of colloids over crystalloids in this clinical scenario.
*Provide oral rehydration therapy to correct dehydration*
- **Oral rehydration therapy (ORT)** is the appropriate first-line treatment for **mild to moderate dehydration** in children who can tolerate oral intake.
- However, ORT is **contraindicated** in patients with **severe dehydration** or **hypovolemic shock**, particularly those with altered mental status, inability to drink, or hemodynamic instability.
- This patient's drowsiness, hypotension, and signs of shock require immediate IV resuscitation; ORT would be too slow and potentially dangerous.
*Give initial IV bolus of 2 L of Ringer's lactate, followed by packed red cells, fresh frozen plasma, and platelets in a ratio of 1:1:1*
- A 2-liter bolus is **excessive and dangerous** for a 7-year-old child (average weight ~23 kg); the appropriate initial bolus is **20 mL/kg** (~460 mL), which can be repeated based on response.
- The **1:1:1 massive transfusion protocol** (packed RBCs, FFP, platelets) is indicated for **hemorrhagic shock** with significant blood loss, not for hypovolemic shock from dehydration.
- There is no evidence of bleeding or coagulopathy in this patient; blood products are not indicated.
*Give antidiarrheal drugs*
- **Antidiarrheal agents** (loperamide, diphenoxylate) are **contraindicated** in young children with acute infectious diarrhea, as they can prolong illness, increase risk of complications (toxic megacolon, bacterial overgrowth), and mask serious underlying conditions.
- The priority in severe dehydration is **fluid and electrolyte resuscitation**, not stopping the diarrhea.
- The diarrhea typically resolves once the underlying infection is controlled and hydration is restored.
