A 22-month-old girl is brought to the emergency department with a 24-hour history of fever, irritability, and poor feeding. The patient never experienced such an episode in the past. She met the normal developmental milestones, and her vaccination history is up-to-date. She takes no medications, currently. Her temperature is 38.9°C (102.0°F). An abdominal examination reveals general tenderness without organomegaly. The remainder of the physical examination shows no abnormalities. Laboratory studies show the following results:
Urine
Blood 1+
WBC 10–15/hpf
Bacteria Many
Nitrite Positive
Urine culture from a midstream collection reveals 100,000 CFU/mL of Escherichia coli. Which of the following interventions is the most appropriate next step in evaluation?
Q92
A 4-year-old boy is brought to the physician in December for episodic shortness of breath and a nonproductive cough for 3 months. These episodes frequently occur before sleeping, and he occasionally wakes up because of difficulty breathing. His mother also reports that he became short of breath while playing with his friends at daycare on several occasions. He is allergic to peanuts. He is at the 55th percentile for height and weight. Vital signs are within normal limits. Examination shows mild scattered wheezing in the thorax. An x-ray of the chest shows no abnormalities. Which of the following is the most likely diagnosis?
Q93
A 9-year-old boy with cystic fibrosis (CF) presents to the clinic with fever, increased sputum production, and cough. The vital signs include: temperature 38.0°C (100.4°F), blood pressure 126/74 mm Hg, heart rate 103/min, and respiratory rate 22/min. His physical examination is significant for short stature, thin body frame, decreased breath sounds bilateral, and a 2/6 holosystolic murmur heard best on the upper right sternal border. His pulmonary function tests are at his baseline, and his sputum cultures reveal Pseudomonas aeruginosa. What is the best treatment option for this patient?
Q94
A 3-year-old girl presents with delayed growth, anemia, and jaundice. Her mother reports no personal history of blood clots, but states that the patient's grandmother has been treated for pulmonary embolism and multiple episodes of unexplained pain in the past. The patient's prenatal history is significant for preeclampsia, preterm birth, and a neonatal intensive care unit (NICU) stay of 6 weeks. The vital signs include: temperature 36.7°C (98.0°F), blood pressure 102/54 mm Hg, heart rate 111/min, and respiratory rate 23/min. On physical examination, the pulses are bounding, the complexion is pale, but breath sounds remain clear. Oxygen saturation was initially 81% on room air, with a new oxygen requirement of 4 L by nasal cannula. Upon further examination, her physician notices that her fingers appear inflamed. A peripheral blood smear demonstrates sickle-shaped red blood cells (RBCs). What is the most appropriate treatment for this patient?
Q95
A 4-year-old girl is brought to the pediatrician's office by her parents with a complaint of foul-smelling discharge from one side of her nose for the past 2 weeks. There is no history of trauma to the nose and she was completely fine during her well-child visit last month. She was born at 39 weeks gestation via spontaneous vaginal delivery. She is up to date on all vaccines and is meeting all developmental milestones. Her vital signs are within normal limits. Examination of the nose reveals a mucoid discharge oozing out from the left nostril. The girl panics when the physician tries to use a nasal speculum. Palpation over the facial bones does not reveal any tenderness. An X-ray image of the paranasal sinuses shows no abnormality. Which of the following is the most likely cause of this condition?
Q96
A 5-year-old boy is brought to his physician by his mother for the evaluation of increased bruising for 3 weeks. The mother reports that the patient has also had two episodes of nose bleeding in the last week that subsided spontaneously within a few minutes. The boy was born at term and has been healthy except for an episode of gastroenteritis 5 weeks ago that resolved without treatment. The patient is at the 48th percentile for height and 43rd percentile for weight. He appears healthy and well nourished. His temperature is 36.5°C (97.7°F), pulse is 100/min, and his blood pressure is 100/65 mm Hg. There are a few scattered petechiae over the trunk and back. The remainder of the examination shows no abnormalities. Laboratory studies show:
Hemoglobin 12.5 g/dL
Mean corpuscular volume 88 μm3
Leukocyte count 9,000/mm3
Platelet count 45,000/mm3
Red cell distribution width 14% (N=13%–15%)
A blood smear shows no abnormalities. Which of the following is the most appropriate next step in the management of this patient?
Q97
A 9-year-old girl is brought to the physician by her father because of abnormal movements of her limbs for 4 days. She has had involuntary nonrhythmic movements of her arms and legs, and has been dropping drinking cups and toys. The symptoms are worse when she is agitated, and she rarely experiences them while sleeping. During this period, she has become increasingly irritable and inappropriately tearful. She had a sore throat 5 weeks ago. Her temperature is 37.2°C (99°F), pulse is 102/min, respirations are 20/min, and blood pressure is 104/64 mm Hg. Examination shows occasional grimacing with abrupt purposeless movements of her limbs. Muscle strength and muscle tone are decreased in all extremities. Deep tendon reflexes are 2+ bilaterally. She has a wide-based and unsteady gait. When the patient holds her arms in extension, flexion of the wrists and extension of the metacarpophalangeal joints occurs. When she grips the physician's index and middle fingers with her hands, her grip increases and decreases continuously. The remainder of the examination shows no abnormalities. Which of the following is the most likely underlying cause of these findings?
Q98
After hospitalization for urgent chemotherapy to treat Burkitt’s lymphoma, a 7-year-old boy developed paresthesias of the fingers, toes, and face. Vital signs are taken. When inflating the blood pressure cuff, the patient reports numbness and tingling of the fingers. His blood pressure is 100/65 mm Hg. Respirations are 28/min, pulse is 100/min, and temperature is 36.2℃ (97.2℉). He has excreted 20 mL of urine in the last 6 hours.
Laboratory studies show the following:
Hemoglobin 15 g/dL
Leukocyte count 6000/mm3 with a normal differential serum
K+ 6.5 mEq/L
Ca+ 6.6 mg/dL
Phosphorus 5.4 mg/dL
HCO3− 15 mEq/L
Uric acid 12 mg/dL
Urea nitrogen 54 mg/dL
Creatinine 3.4 mg/dL
Arterial blood gas analysis on room air:
pH 7.30
PCO2 30 mm Hg
O2 saturation 95%
Which of the following is the most likely cause of this patient’s renal condition?
Q99
A 4-year-old boy is brought to the pediatrician with fever, diarrhea and bilateral red eye for 7 days. His parents noted that he has never had an episode of diarrhea this prolonged, but several other children at daycare had been ill. His immunization history is up to date. His vitals are normal except for a temperature of 37.5°C (99°F). A physical exam is significant for mild dehydration, preauricular adenopathy, and bilateral conjunctival injection with watery discharge. What is the most likely diagnosis?
Q100
A 2-year-old girl is brought to her pediatrician’s office with intermittent and severe stomach ache and vomiting for the last 2 days. Last week the whole family had a stomach bug involving a few days of mild fever, lack of appetite, and diarrhea but they have all made a full recovery since. This current pain is different from the type she had during infection. With the onset of pain, the child cries and kicks her legs up in the air or pulls them to her chest. The parents have also observed mucousy stools and occasional bloody stools that are bright red and mucousy. After a while, the pain subsides and she returns to her normal activity. Which of the following would be the next step in the management of this patient?
Infectious Disease US Medical PG Practice Questions and MCQs
Question 91: A 22-month-old girl is brought to the emergency department with a 24-hour history of fever, irritability, and poor feeding. The patient never experienced such an episode in the past. She met the normal developmental milestones, and her vaccination history is up-to-date. She takes no medications, currently. Her temperature is 38.9°C (102.0°F). An abdominal examination reveals general tenderness without organomegaly. The remainder of the physical examination shows no abnormalities. Laboratory studies show the following results:
Urine
Blood 1+
WBC 10–15/hpf
Bacteria Many
Nitrite Positive
Urine culture from a midstream collection reveals 100,000 CFU/mL of Escherichia coli. Which of the following interventions is the most appropriate next step in evaluation?
A. No further testing
B. Voiding cystourethrography
C. Renal and bladder ultrasonography (Correct Answer)
D. Intravenous pyelography
E. Dimercaptosuccinic acid renal scan
Explanation: ***Renal and bladder ultrasonography***
- For a febrile infant or young child (2 to 24 months) with a first **culture-proven urinary tract infection (UTI)**, renal and bladder ultrasonography is the recommended imaging study.
- This imaging is crucial to evaluate for **anatomic abnormalities** of the kidneys and urinary tract that could predispose to recurrent infections or renal damage.
- Current AAP guidelines recommend ultrasound as the **initial imaging modality** to assess for conditions like vesicoureteral reflux (VUR), hydronephrosis, or obstructive uropathy.
*No further testing*
- This option is incorrect because a **febrile UTI** in a young child warrants imaging to rule out **underlying genitourinary abnormalities** that could predispose to recurrent infections or renal damage.
- Skipping further evaluation could miss conditions like **vesicoureteral reflux (VUR)** or obstructive uropathy.
*Voiding cystourethrography*
- **Voiding cystourethrography (VCUG)** was historically recommended for all young children after a first UTI but is now reserved for specific situations, such as **abnormal renal/bladder ultrasound findings** or recurrent UTIs.
- VCUG involves radiation exposure and catheterization, making it less favorable as a first-line imaging study.
*Intravenous pyelography*
- **Intravenous pyelography (IVP)** involves intravenous contrast and radiation, making it an **invasive and high-radiation study** that has largely been replaced by ultrasound and CT for evaluating the urinary tract.
- It is not recommended as the initial imaging of choice for a child with a first UTI due to its **risks and availability of safer alternatives**.
*Dimercaptosuccinic acid renal scan*
- A **dimercaptosuccinic acid (DMSA) renal scan** is primarily used to detect **renal scarring** and assesses differential renal function.
- While it can be useful in identifying long-term consequences of UTIs, it is not the primary imaging study for initial evaluation of **ureteral or bladder abnormalities** in a first febrile UTI.
Question 92: A 4-year-old boy is brought to the physician in December for episodic shortness of breath and a nonproductive cough for 3 months. These episodes frequently occur before sleeping, and he occasionally wakes up because of difficulty breathing. His mother also reports that he became short of breath while playing with his friends at daycare on several occasions. He is allergic to peanuts. He is at the 55th percentile for height and weight. Vital signs are within normal limits. Examination shows mild scattered wheezing in the thorax. An x-ray of the chest shows no abnormalities. Which of the following is the most likely diagnosis?
A. Primary ciliary dyskinesia
B. Tracheomalacia
C. Cardiac failure
D. Asthma (Correct Answer)
E. Cystic fibrosis
Explanation: ***Asthma***
- The recurrent episodes of **shortness of breath** and **nonproductive cough**, occurring for 3 months, frequently before sleeping, and triggered by activity (playing), are classic symptoms of **asthma**.
- The presence of **mild scattered wheezing** on examination and an **unremarkable chest x-ray** further support this diagnosis in a 4-year-old child.
*Primary ciliary dyskinesia*
- Characterized by chronic respiratory infections, **bronchiectasis**, and typically a **wet cough** with sputum production, which is not described.
- Often associated with **situs inversus** and other anomalies, and symptoms are usually persistent rather than episodic and triggered.
*Tracheomalacia*
- Presents with a **barking cough**, **stridor**, and often **worsens with crying** or agitation, due to airway collapse.
- Symptoms are usually consistent from birth or early infancy and not typically episodic wheezing triggered by activity.
*Cardiac failure*
- Would likely present with additional signs such as **poor weight gain**, **fatigue**, **tachycardia**, or a **cardiac murmur**, none of which are mentioned.
- A normal chest x-ray also makes significant cardiac failure unlikely to be the primary cause of respiratory symptoms.
*Cystic fibrosis*
- Typically presents with **failure to thrive**, **malabsorption**, **recurrent pulmonary infections**, and a **chronic productive cough** due to thick mucus.
- The patient's normal height and weight percentiles and nonproductive cough make cystic fibrosis less likely.
Question 93: A 9-year-old boy with cystic fibrosis (CF) presents to the clinic with fever, increased sputum production, and cough. The vital signs include: temperature 38.0°C (100.4°F), blood pressure 126/74 mm Hg, heart rate 103/min, and respiratory rate 22/min. His physical examination is significant for short stature, thin body frame, decreased breath sounds bilateral, and a 2/6 holosystolic murmur heard best on the upper right sternal border. His pulmonary function tests are at his baseline, and his sputum cultures reveal Pseudomonas aeruginosa. What is the best treatment option for this patient?
A. Dornase alfa 2.5 mg as a single-use
B. Oral cephalexin for 14 days
C. Inhaled tobramycin for 28 days (Correct Answer)
D. Minocycline for 28 days
E. Sulfamethoxazole and trimethoprim for 14 days
Explanation: ***Inhaled tobramycin for 28 days***
- This patient presents with a **mild pulmonary exacerbation** of **cystic fibrosis (CF)**, characterized by fever, increased sputum production, and the isolation of **Pseudomonas aeruginosa** from sputum cultures.
- The **pulmonary function tests (PFTs) at baseline** indicate this is a **mild exacerbation** that can be managed in the **outpatient setting**.
- **Inhaled tobramycin** is the appropriate first-line treatment for **mild-to-moderate exacerbations** and for **chronic suppressive therapy** of **Pseudomonas aeruginosa** infections in CF patients.
- It is effective in improving lung function, reducing bacterial load, and decreasing exacerbation frequency with minimal systemic toxicity.
- More severe exacerbations (significant PFT decline, respiratory distress) would require **IV antipseudomonal antibiotics**.
*Dornase alfa 2.5 mg as a single-use*
- **Dornase alfa** (DNase) is a mucolytic agent used in CF to reduce sputum viscosity and improve airway clearance by breaking down extracellular DNA in mucus.
- While beneficial for **chronic airway clearance therapy**, it is not an antibiotic and does not directly treat the **bacterial infection** causing the current exacerbation.
*Oral cephalexin for 14 days*
- **Cephalexin** is a first-generation cephalosporin that primarily targets **gram-positive bacteria** (such as Staphylococcus aureus) and some **gram-negative bacteria**.
- It is **completely ineffective against Pseudomonas aeruginosa**, which is intrinsically resistant to first-generation cephalosporins.
*Minocycline for 28 days*
- **Minocycline** is a **tetracycline antibiotic** with activity against many bacteria, including some **atypical pathogens** and **Staphylococcus aureus**.
- However, it is **not effective against Pseudomonas aeruginosa**, which is intrinsically resistant to tetracyclines and is a common and aggressive pathogen in CF patients.
*Sulfamethoxazole and trimethoprim for 14 days*
- **Sulfamethoxazole and trimethoprim** (TMP-SMX, Bactrim) is an antibiotic combination effective against various bacteria, including some **gram-negative organisms** and **Staphylococcus aureus**.
- It does **not provide adequate coverage for Pseudomonas aeruginosa**, making it an inappropriate choice for this patient's documented infection.
Question 94: A 3-year-old girl presents with delayed growth, anemia, and jaundice. Her mother reports no personal history of blood clots, but states that the patient's grandmother has been treated for pulmonary embolism and multiple episodes of unexplained pain in the past. The patient's prenatal history is significant for preeclampsia, preterm birth, and a neonatal intensive care unit (NICU) stay of 6 weeks. The vital signs include: temperature 36.7°C (98.0°F), blood pressure 102/54 mm Hg, heart rate 111/min, and respiratory rate 23/min. On physical examination, the pulses are bounding, the complexion is pale, but breath sounds remain clear. Oxygen saturation was initially 81% on room air, with a new oxygen requirement of 4 L by nasal cannula. Upon further examination, her physician notices that her fingers appear inflamed. A peripheral blood smear demonstrates sickle-shaped red blood cells (RBCs). What is the most appropriate treatment for this patient?
A. Intravenous immunoglobulin
B. Corticosteroids
C. Epoetin
D. Hydroxyurea (Correct Answer)
E. Darbepoetin
Explanation: ***Hydroxyurea***
- This patient presents with symptoms highly suggestive of **sickle cell disease (SCD)**, including **delayed growth, anemia, jaundice, oxygen desaturation**, and **sickle-shaped red blood cells** on peripheral smear. **Hydroxyurea** is a first-line treatment for SCD in children and adults to reduce the frequency of **pain crises, acute chest syndrome**, and the need for transfusions.
- Hydroxyurea works by increasing the production of **fetal hemoglobin (HbF)**, which inhibits the sickling of red blood cells and improves their oxygen-carrying capacity. It also has anti-inflammatory properties, which can help manage SCD complications.
*Intravenous immunoglobulin*
- **Intravenous immunoglobulin (IVIG)** is primarily used in conditions involving immune dysfunction, such as **Kawasaki disease**, **immune thrombocytopenia**, or certain primary immunodeficiencies.
- There is no indication of an **immune-mediated disorder** or infection requiring IVIG in this patient's presentation of sickle cell crisis.
*Corticosteroids*
- **Corticosteroids** are potent anti-inflammatory and immunosuppressive agents often used in conditions like asthma, autoimmune disorders, or allergic reactions.
- While inflammation plays a role in sickle cell crises, corticosteroids are generally not a primary treatment for the underlying disease mechanism and can have significant side effects with long-term use.
*Epoetin*
- **Epoetin** is a recombinant form of **erythropoietin**, a hormone that stimulates red blood cell production. It is used to treat anemia associated with chronic kidney disease or chemotherapy.
- In sickle cell disease, the anemia is due to increased red blood cell destruction (hemolysis) and dysfunctional red blood cells, rather than *insufficient erythropoietin production*, making epoetin generally ineffective.
*Darbepoetin*
- **Darbepoetin** is a longer-acting form of **epoetin**, primarily used to treat anemia in chronic kidney disease, chemotherapy-induced anemia, or certain myelodysplastic syndromes.
- Similar to epoetin, darbepoetin is not a primary treatment for the **hemolytic anemia** characteristic of sickle cell disease, where the problem lies with abnormal hemoglobin and cell shape rather than erythropoietin deficiency.
Question 95: A 4-year-old girl is brought to the pediatrician's office by her parents with a complaint of foul-smelling discharge from one side of her nose for the past 2 weeks. There is no history of trauma to the nose and she was completely fine during her well-child visit last month. She was born at 39 weeks gestation via spontaneous vaginal delivery. She is up to date on all vaccines and is meeting all developmental milestones. Her vital signs are within normal limits. Examination of the nose reveals a mucoid discharge oozing out from the left nostril. The girl panics when the physician tries to use a nasal speculum. Palpation over the facial bones does not reveal any tenderness. An X-ray image of the paranasal sinuses shows no abnormality. Which of the following is the most likely cause of this condition?
A. Bilateral maxillary sinusitis
B. Septal hematoma
C. Nasal foreign body (Correct Answer)
D. Nasal polyp
E. Nasal tumor
Explanation: ***Nasal foreign body***
- A **unilateral, foul-smelling nasal discharge** in a young child without a history of trauma, especially when a child resists nasal examination, is highly suggestive of a nasal foreign body.
- Young children often insert small objects into their nostrils, which can lead to inflammation, infection, and subsequent discharge.
*Bilateral maxillary sinusitis*
- **Sinusitis** typically presents with bilateral symptoms, facial pain (which is absent here), and often follows an upper respiratory infection.
- The discharge in sinusitis is usually purulent and not consistently foul-smelling and unilateral as described.
*Septal hematoma*
- A **septal hematoma** is typically caused by nasal trauma and presents with nasal obstruction, pain, and swelling, but not typically a foul-smelling discharge.
- Untreated, it can lead to complications like septal abscess or cartilage necrosis, but its presentation is distinct from this case.
*Nasal polyp*
- **Nasal polyps** are rare in children and usually present with chronic nasal obstruction, rhinorrhea, and sometimes epistaxis, but not typically a foul-smelling unilateral discharge in a 4-year-old.
- They are often associated with conditions like **cystic fibrosis** in children.
*Nasal tumor*
- While a **nasal tumor** can cause unilateral nasal symptoms, it is a rare cause of foul-smelling discharge in a 4-year-old.
- Tumors commonly present with **unilateral epistaxis**, persistent obstruction, or facial swelling, which are not the primary symptoms here.
Question 96: A 5-year-old boy is brought to his physician by his mother for the evaluation of increased bruising for 3 weeks. The mother reports that the patient has also had two episodes of nose bleeding in the last week that subsided spontaneously within a few minutes. The boy was born at term and has been healthy except for an episode of gastroenteritis 5 weeks ago that resolved without treatment. The patient is at the 48th percentile for height and 43rd percentile for weight. He appears healthy and well nourished. His temperature is 36.5°C (97.7°F), pulse is 100/min, and his blood pressure is 100/65 mm Hg. There are a few scattered petechiae over the trunk and back. The remainder of the examination shows no abnormalities. Laboratory studies show:
Hemoglobin 12.5 g/dL
Mean corpuscular volume 88 μm3
Leukocyte count 9,000/mm3
Platelet count 45,000/mm3
Red cell distribution width 14% (N=13%–15%)
A blood smear shows no abnormalities. Which of the following is the most appropriate next step in the management of this patient?
A. Romiplostim therapy
B. Splenectomy
C. Observation (Correct Answer)
D. Intravenous immunoglobulin therapy
E. Antiplatelet antibody testing
Explanation: ***Observation***
- This patient presents with classic signs of **immune thrombocytopenia (ITP)**: recent viral illness (gastroenteritis), bruising, nosebleeds, and isolated **thrombocytopenia** with otherwise normal labs and peripheral smear.
- In a child with mild symptoms and a platelet count >20,000/mm³, **observation** is typically the most appropriate initial management, as ITP in children often resolves spontaneously within 6 months.
*Romiplostim therapy*
- This is a **thrombopoietin receptor agonist** used for chronic ITP (persisting for >12 months) that has been refractory to other treatments like corticosteroids, IVIG, or splenectomy.
- It is not indicated for initial management of acute ITP, especially in children with mild symptoms.
*Splenectomy*
- **Splenectomy** is reserved for cases of **chronic ITP** refractory to medical therapy or in patients with severe bleeding and high risk.
- It carries surgical risks and is not indicated as a first-line treatment, especially for mild, acute ITP in children.
*Intravenous immunoglobulin therapy*
- **IVIG** is considered for ITP patients with significant bleeding, a low platelet count (<20,000/mm³), or those at high risk for hemorrhage.
- Given this patient's relatively benign symptoms (petechiae, mild nosebleeds) and platelet count of 45,000/mm³, IVIG is not immediately warranted.
*Antiplatelet antibody testing*
- While **antiplatelet antibodies** are often involved in the pathophysiology of ITP, their testing is generally **not necessary for diagnosis**, as the diagnosis is primarily clinical, based on isolated thrombocytopenia after excluding other causes.
- The presence or absence of these antibodies does not change the initial management strategy for acute ITP.
Question 97: A 9-year-old girl is brought to the physician by her father because of abnormal movements of her limbs for 4 days. She has had involuntary nonrhythmic movements of her arms and legs, and has been dropping drinking cups and toys. The symptoms are worse when she is agitated, and she rarely experiences them while sleeping. During this period, she has become increasingly irritable and inappropriately tearful. She had a sore throat 5 weeks ago. Her temperature is 37.2°C (99°F), pulse is 102/min, respirations are 20/min, and blood pressure is 104/64 mm Hg. Examination shows occasional grimacing with abrupt purposeless movements of her limbs. Muscle strength and muscle tone are decreased in all extremities. Deep tendon reflexes are 2+ bilaterally. She has a wide-based and unsteady gait. When the patient holds her arms in extension, flexion of the wrists and extension of the metacarpophalangeal joints occurs. When she grips the physician's index and middle fingers with her hands, her grip increases and decreases continuously. The remainder of the examination shows no abnormalities. Which of the following is the most likely underlying cause of these findings?
A. Autosomal recessive genetic mutation
B. Tumor in the posterior fossa
C. Cerebral viral infection
D. Trinucleotide repeat mutation
E. Antibody cross-reactivity (Correct Answer)
Explanation: ***Antibody cross-reactivity***
- The patient's symptoms (abnormal, involuntary movements, emotional lability, recent sore throat) are classic for **Sydenham chorea**, a manifestation of **acute rheumatic fever**. This condition is caused by **antibodies** produced against *Streptococcus pyogenes* infection that cross-react with basal ganglia proteins.
- The examination findings, such as **milkmaid grip** and **pronator drift** (flexion of wrists and extension of metacarpophalangeal joints), are highly indicative of chorea.
*Autosomal recessive genetic mutation*
- While conditions like **Wilson's disease** (hepatolenticular degeneration) can cause chorea, they typically present with liver disease, Kayser-Fleischer rings, and a more insidious onset, which are not described here.
- **Neuroacanthocytosis** is another rare recessive disorder causing chorea, but it involves acanthocytes on blood smear and other neurological features not suggested in the vignette.
*Tumor in the posterior fossa*
- Posterior fossa tumors, such as medulloblastomas or astrocytomas, would more commonly present with signs of **increased intracranial pressure** (headache, vomiting), **ataxia**, and focal neurological deficits, rather than generalized choreiform movements as the primary symptom.
- Chorea is typically associated with basal ganglia dysfunction, which is not the primary site of posterior fossa tumors.
*Cerebral viral infection*
- A cerebral viral infection (encephalitis) could cause neurological symptoms, but it would typically involve fever, altered mental status, seizures, and signs of meningoencephalitis, which are not the predominant features in this case.
- While encephalitis can sometimes cause movement disorders, the specific presentation with antecedent sore throat and classic choreiform movements points more strongly to **Sydenham chorea**.
*Trinucleotide repeat mutation*
- **Huntington's disease** is a classic cause of chorea due to a trinucleotide repeat expansion, but it is an **autosomal dominant** disorder with a much later onset, typically in adulthood (30s-50s).
- Juvenile forms of Huntington's exist but are rare and would likely involve other cognitive and psychiatric symptoms.
Question 98: After hospitalization for urgent chemotherapy to treat Burkitt’s lymphoma, a 7-year-old boy developed paresthesias of the fingers, toes, and face. Vital signs are taken. When inflating the blood pressure cuff, the patient reports numbness and tingling of the fingers. His blood pressure is 100/65 mm Hg. Respirations are 28/min, pulse is 100/min, and temperature is 36.2℃ (97.2℉). He has excreted 20 mL of urine in the last 6 hours.
Laboratory studies show the following:
Hemoglobin 15 g/dL
Leukocyte count 6000/mm3 with a normal differential serum
K+ 6.5 mEq/L
Ca+ 6.6 mg/dL
Phosphorus 5.4 mg/dL
HCO3− 15 mEq/L
Uric acid 12 mg/dL
Urea nitrogen 54 mg/dL
Creatinine 3.4 mg/dL
Arterial blood gas analysis on room air:
pH 7.30
PCO2 30 mm Hg
O2 saturation 95%
Which of the following is the most likely cause of this patient’s renal condition?
A. Direct tubular toxicity through filtered light chains
B. Pigment-induced nephropathy
C. Deposition of calcium phosphate in the kidney
D. Intense renal vasoconstriction and volume depletion
E. Precipitation of uric acid in renal tubules/tumor lysis syndrome (Correct Answer)
Explanation: ***Precipitation of uric acid in renal tubules/tumor lysis syndrome***
- This patient's laboratory values, including **hyperkalemia** (K+ 6.5 mEq/L), **hyperphosphatemia** (Phosphorus 5.4 mg/dL), **hypocalcemia** (Ca+ 6.6 mg/dL), and **hyperuricemia** (Uric acid 12 mg/dL), are classic signs of **tumor lysis syndrome (TLS)**. TLS is caused by the rapid breakdown of tumor cells, commonly seen after chemotherapy for highly proliferative cancers like Burkitt's lymphoma.
- The elevated **uric acid** levels lead to the precipitation of uric acid crystals in the renal tubules, causing **acute kidney injury (AKI)**, as evidenced by the high creatinine (3.4 mg/dL) and oliguria (20 mL urine in 6 hours).
*Direct tubular toxicity through filtered light chains*
- This mechanism is characteristic of **myeloma kidney**, where light chains filtered by the glomeruli are directly toxic to the renal tubules, causing kidney damage.
- The patient's diagnosis of Burkitt's lymphoma and the rapid onset of symptoms after chemotherapy point away from light chain nephropathy.
*Pigment-induced nephropathy*
- This condition involves the precipitation of pigments like **myoglobin** (from rhabdomyolysis) or **hemoglobin** (from hemolysis) in the renal tubules, causing obstruction and kidney injury.
- While AKI is present, there is no evidence of rhabdomyolysis (e.g., elevated CK) or significant hemolysis to suggest pigment nephropathy.
*Deposition of calcium phosphate in the kidney*
- **Calcium phosphate deposition** can occur in conditions like **hypercalcemia** or sometimes in TLS due to the inverse relationship between calcium and phosphate; however, the primary driver for AKI in TLS is uric acid precipitation.
- Though **hypocalcemia** and **hyperphosphatemia** are present, the direct cause of renal failure in this scenario is driven by the significant hyperuricemia.
*Intense renal vasoconstriction and volume depletion*
- While **renal vasoconstriction** and **volume depletion** can lead to acute kidney injury (prerenal AKI) and are possible in a hospitalized patient, they do not explain the specific electrolyte abnormalities (hyperkalemia, hyperphosphatemia, hypocalcemia, hyperuricemia) seen in this case.
- The patient's blood pressure (100/65 mmHg) is not severely hypotensive, and while urine output is low, the comprehensive metabolic picture points more strongly to an intrinsic renal issue due to tumor lysis syndrome.
Question 99: A 4-year-old boy is brought to the pediatrician with fever, diarrhea and bilateral red eye for 7 days. His parents noted that he has never had an episode of diarrhea this prolonged, but several other children at daycare had been ill. His immunization history is up to date. His vitals are normal except for a temperature of 37.5°C (99°F). A physical exam is significant for mild dehydration, preauricular adenopathy, and bilateral conjunctival injection with watery discharge. What is the most likely diagnosis?
A. C. difficile colitis
B. Rotavirus infection
C. Adenovirus infection (Correct Answer)
D. Vibrio parahaemolyticus infection
E. Norovirus infection
Explanation: ***Adenovirus infection***
- The combination of **fever**, **prolonged diarrhea**, **bilateral conjunctivitis with watery discharge**, and **preauricular adenopathy** in a young child strongly suggests adenovirus infection, particularly the **pharyngoconjunctival fever** syndrome.
- This virus is highly contagious and commonly spreads in communal settings like daycares, aligning with the "several other children at daycare had been ill" observation.
*C. difficile colitis*
- While it causes diarrhea, **_C. difficile_ colitis** is typically associated with **antibiotic use** or hospitalization, and usually presents with more severe, often bloody, diarrhea and abdominal pain, without conjunctivitis or preauricular adenopathy as primary features.
- It is less common as a primary cause of prolonged diarrhea in healthy, ambulatory young children unless there's a clear predisposing factor.
*Rotavirus infection*
- **Rotavirus** is a common cause of **severe watery diarrhea** and vomiting in young children, often accompanied by fever.
- However, **conjunctivitis** and **preauricular adenopathy** are not typical symptoms of rotavirus infection, making it a less likely diagnosis in this scenario.
*Vibrio parahaemolyticus infection*
- **_Vibrio parahaemolyticus_** typically causes **gastroenteritis** after consumption of **contaminated seafood**, presenting with watery diarrhea, abdominal cramps, and fever.
- This type of infection does not commonly cause conjunctivitis or preauricular adenopathy, nor is the daycare setting typical for its transmission.
*Norovirus infection*
- **Norovirus** is a common cause of acute **gastroenteritis** outbreaks, characterized by sudden onset of vomiting and watery diarrhea, sometimes with fever and abdominal cramps.
- Similar to rotavirus, **conjunctivitis** and **preauricular adenopathy** are not characteristic features of norovirus infection.
Question 100: A 2-year-old girl is brought to her pediatrician’s office with intermittent and severe stomach ache and vomiting for the last 2 days. Last week the whole family had a stomach bug involving a few days of mild fever, lack of appetite, and diarrhea but they have all made a full recovery since. This current pain is different from the type she had during infection. With the onset of pain, the child cries and kicks her legs up in the air or pulls them to her chest. The parents have also observed mucousy stools and occasional bloody stools that are bright red and mucousy. After a while, the pain subsides and she returns to her normal activity. Which of the following would be the next step in the management of this patient?
A. Abdominal radiograph
B. Air enema (Correct Answer)
C. Abdominal CT scan
D. Surgical reduction
E. Observe for 24 hours
Explanation: ***Air enema***
- The clinical presentation with intermittent abdominal pain, leg drawing to the chest, "currant jelly" stools (bloody and mucousy), and a recent viral illness is highly suggestive of **intussusception**. An **air enema** is the diagnostic and therapeutic modality of choice for intussusception.
- It uses pneumatic pressure to reduce the telescoping of the bowel, and if successful, avoids the need for surgery.
*Abdominal radiograph*
- An **abdominal radiograph** may show signs of obstruction or a "target sign" (if present), but it is not sensitive or specific enough to definitively diagnose intussusception.
- It is primarily used to rule out perforation before performing an air enema if there are concerns about peritonitis.
*Abdominal CT scan*
- While an **abdominal CT scan** can diagnose intussusception, it exposes the child to significant radiation and is not typically the first-line imaging modality.
- It is usually reserved for cases where other diagnostic methods are inconclusive or if complications like perforation are suspected.
*Surgical reduction*
- **Surgical reduction** is indicated if an air enema fails to reduce the intussusception, if there are signs of bowel perforation or peritonitis, or if the patient is unstable.
- It is an invasive procedure and should not be the initial step in management unless there are clear contraindications to pneumatic reduction.
*Observe for 24 hours*
- Observing the child for 24 hours without intervention is inappropriate and can lead to serious complications, such as **bowel ischemia, necrosis, perforation, and sepsis**.
- Intussusception is a medical emergency that requires prompt diagnosis and treatment.
