Block 13 Explanations
1) A 1400-g infant, born at 35 weeks’ gestation, is 42 cm in length and a has a head circumference of 28 cm. One day after birth, she becomes very irritable, tremulous, and inconsolable. Her cry is high-pitched. Her pulse is 174/min. There are no dysmorphic facial features. To which of the following substances was this newborn most likely exposed in utero?
A. Alcohol
B. Barbiturates
C. Cocaine
D. Marijuana
E. Opiates
Explanation:
The correct answer is
C. The most commonly abused drug by pregnant mothers is cocaine. Infants are usually small for gestational age (SGA) and sometimes have microcephaly and neurodevelopmental abnormalities. Exposed infants are very irritable and inconsolable in the withdrawal period. Their cries are often high-pitched. They are also at increased risk of sudden infant death syndrome (SIDS). Periventricular leukomalacia (a CNS ischemic lesion) is also associated with cocaine exposure. Alcohol (choice A) abuse during pregnancy causes fetal alcohol syndrome. It is characterized by failure to thrive, cardiac defects, facial dysmorphic features (such as narrow forehead, microphthalmia, short palpebral fissures, and micrognathia), and neurologic abnormalities. Barbiturate (choice B) use during pregnancy causes the infant to have limb anomalies, mental retardation, nail hypoplasia, and some dysmorphic features, such as a short nose and a low nasal bridge. It is not usually associated with low birth weight and microcephaly. There is no clear evidence that marijuana (choice D) use during pregnancy is associated with any teratogenic effects on the infant in humans. In animal studies, however, it has been associated with fetal growth restriction and teratogenesis. Opiate (choice E) abuse during pregnancy is associated with a high incidence of obstetric complications, such as placental abruption, preterm labor, and fetal growth restriction. Tremors, irritability, vomiting, and diarrhea present in the neonatal period.
2) A 14-year-old boy is brought to the emergency room because of persistent midepigastric pain for two days. The pain is getting no better, yet it is no worse, and radiates to his back. The boy also has had fever, as well as nausea and vomiting that is worse when his temperature rises in the afternoon. On examination, his temperature is 39.2 C (102.5 F) and there is marked upper abdominal tenderness with guarding. Mild abdominal distention is present with no audible bowel sounds. A complete blood count reveals an elevated leukocyte count and a normal serum amylase. Which of the following is the most likely diagnosis?
A. Fitz-Hugh-Curtis syndrome
B. Intussusception
C. Wilms tumor
D. Pancreatitis
E. Pyelonephritis
Explanation:
The correct answer is
D. Pancreatitis is not always an easy diagnosis. The history of this boy is particularly suspect, even with a normal serum amylase. Nearly one-third of all patients with acute pancreatitis have a normal serum amylase. An abdominal ultrasound may be useful in revealing an enlarged pancreas. This young man is unlikely to have Fitz-Hugh-Curtis syndrome (choice A). Classically, Fitz-Hugh-Curtis syndrome is an extrapelvic manifestation of pelvic inflammatory disease in sexually active women. It is a perihepatitis consisting of adhesions between the liver capsule and the diaphragm or the anterior peritoneal surface. It was originally thought to be caused solely by Neisseria gonorrhoeae, but recent studies have shown that Chlamydia trachomatis and other organisms may also be etiologies. The Fitz-Hugh-Curtis syndrome has rarely been reported in men, so a sexual history should be obtained in this case. Intussusception (choice B) is not high on the list of differential diagnoses. The typical age for intussusception is in infancy, especially 6 to 12 months of age. This young man has persistent abdominal pain with fever, making this an unlikely diagnosis. Wilms tumor (choice C) is also unlikely in this case scenario. Wilms tumor usually occurs in early childhood, age 2 or 3 years. Although Wilms tumor is more prevalent in males, the usual presenting signs include an asymptomatic abdominal mass and hematuria. Pyelonephritis (choice E) typically presents with high fever, chills, and back pain. Although a urinalysis should be performed in this young man, the symptoms of midepigastric pain suggest an upper gastrointestinal problem, not pyelonephritis.
3) A baby is born at 34 weeks gestation. The amniotic fluid is brown and murky. The baby has low APGAR scores and appears to be septic, with lethargy, apnea, bradycardia, and temperature instability. The mother lives on a farm and gives a history of a flu-like illness one month before delivery. Gram’s stain of a smear from the mother’s cervix demonstrates abundant, pleomorphic, gram-variable coccobacillary forms. Which of the following is the most likely diagnosis?
A. Congenital cytomegalovirus infection
B. Congenital rubella
C. Congenital syphilis
D. Neonatal herpes simplex infection
E. Neonatal listeriosis
Explanation:
The correct answer is
E.Listeria monocytogenes, the causative agent of listeriosis, can be acquired by mothers exposed to unpasteurized dairy products or raw vegetables exposed to cattle or sheep manure. The condition can cause a febrile, flu-like disease in the mother. The affects on the fetus and newborn depend on the timing of the infection. The bacteria have a predilection for causing amnionitis, which may then produce abortion, stillbirth, or neonatal sepsis. The presence of brown, murky amniotic fluid may be a helpful diagnostic clue (and a clue on test questions). Disseminated disease in the fetus can cause granuloma formation (with associated tissue destruction) in many tissues, including liver, adrenal glands, lymphatic tissue, lungs, and brain; the term granulomatosis infantiseptica is sometimes used in these cases. The mortality rate in affected infants ranges from 10 to 50% (higher in early onset disease). Some authors recommend blood and cervical culture in pregnant women who have a potential exposure and develop a flu-like illness. Congenital cytomegalovirus infection (choice A) can cause asymptomatic to mild to severe disease in neonates; look for a reference to flu-like symptoms during pregnancy in the question stem. Another clue with some specificity (also present in toxoplasmosis) is a reference to periventricular calcifications. (A good negative clue is no reference to cats, which would have suggested toxoplasmosis.) Congenital rubella (choice B) can cause multiple severe problems in infants; look for a reference to the mother having had a rash during pregnancy. Congenital syphilis (choice C) can also cause devastating disease in newborns; look for references to rash involving palms and soles, Hutchinson’s molars, or bone deformities, including saber shin. Neonatal herpes simplex infection (choice D) can be a devastating infection of the neonate; look for skin vesicles and often prominent neurologic involvement.
4) An infant is born prematurely and is small for gestational age. At birth, the infant is obviously ill with jaundice, fever, hepatosplenomegaly, myocarditis, and rashes. Neurologic involvement is prominent, with hydrocephalus, intracranial calcifications, and seizures. The mother has a cat and continued to clean the cat’s litter box during the pregnancy. Which of the following is the most likely causative agent?
A. Cytomegalovirus
B. Herpes simplex
C. Rubella virus
D. Toxoplasma
E. Treponema pallidum
Explanation:
The correct answer is
D. This is congenital toxoplasmosis. It can look like other severe congenital infections, so a very helpful clue is that there will usually be a reference to “cat feces” in the question stem, which is the usual clinical source of the infection. Affected babies can be asymptomatic or can have severe, disseminated disease which may manifest as growth retardation, jaundice, hepatosplenomegaly, myocarditis, pneumonitis, rash, or neurologic involvement (hydrocephalus, microcephaly, intracranial calcifications, seizures, chorioretinitis). Severely affected babies also have thrombocytopenia, lymphocytosis, monocytosis, and elevated eosinophils. Treatment is with combination antibiotic therapy, including pyrimethamine, sulfadiazine, and leucovorin. Cytomegalovirus (choice A) can cause congenital and perinatal infections that can be asymptomatic or can cause intrauterine growth retardation, microcephaly, jaundice, hepatosplenomegaly, periventricular calcifications, chorioretinitis, and pneumonitis. Herpes simplex (choice B) can cause congenital and perinatal infection, which may cause skin vesicles, disseminated disease, and neurologic disease. Rubella virus (choice C) can produce congenital disease that can cause fetal death or growth retardation, encephalitis, cataracts, cardiac defects, hearing defects, and hepatosplenomegaly. Treponema pallidum (choice E), the causative agent of syphilis, can cause rash, lymphadenopathy, hepatosplenomegaly, gummas of the face, bony lesions, and neurosyphilis in infants.
5) A 9-month-old infant is seen in the pediatrician’s office because of failure to gain weight. Her length and weight are both below the 5th percentile at her age. The patient’s chart indicates that at the age of age of 6 months, her length and weight were at the 50th percentile. A careful history reveals that the mother returned to work when the infant was 6 months old, and the grandmother assumed the care of the infant most of the time since then. She is receiving 6-8 oz of iron-fortified, cow protein-based formula every 4 hours. Which of the following is the best initial step in the management of this infant?
A. Ask how the formula is mixed
B. Obtain a detailed family history for lactose intolerance
C. Obtain a stool specimen
D. Obtain a sweat chloride test
E. Obtain a urinalysis
Explanation:
The correct answer is
A. This 9-month-old infant presents with failure to thrive, which is determined by the decline in her length and weight to below the 5th percentile. Failure to thrive can be either organic or inorganic (i.e., social). Although it is important to identify the causes of organic failure to thrive, most cases are inorganic. In this clinical vignette, since the reduction of weight happens after the mother returned to work, an inorganic cause is likely. One of the most common causes of failure to thrive is improper preparation of the formula, resulting either from an incorrect water-to-formula ratio or from poor mixing techniques. In addition to obtaining a detailed history of how the formula is mixed, it might be very useful to have the caretaker actually demonstrate how he or she prepares the formula. In this case, the most likely reason that the infant has failure to thrive is that the grandmother has improperly mixed the formula. Lactose intolerance (choice B) is an uncommon cause of failure to thrive. It usually presents with abdominal pain, bloating, and diarrhea. Obtaining a stool specimen (choice C), sweat chloride test (choice D), or urinalysis (choice E) might be helpful if no identifiable inorganic causes of failure to thrive are identified. Urinalysis is helpful in screening for renal disease. A sweat chloride test is used to detect cystic fibrosis. Stool specimens can be useful in a great variety of gastrointestinal disorders, such as gastroenteritis, parasitic infection, and fat malabsorption.
6) A 30-hour-old infant has not passed meconium since birth. He was full term with a birth weight of 3856 g (8 lb 8 oz). The pregnancy was uncomplicated. The baby appears well with no respiratory distress. Slight abdominal distention is noted. Rectal examination reveals a slightly tight rectum and results in a greenish gush of stool. Which of the following tests will probably confirm the likely diagnosis?
A. A stool culture
B. A rectal biopsy
C. A barium enema
D. An alpha1-antitrypsin level
E. A serum TSH level
Explanation:
The correct answer is
B. Hirschsprung disease or congenital aganglionic megacolon is caused by a congenital absence of the ganglion cells of both the Meissner and Auerbach plexuses. It is the most common cause of lower intestinal obstruction in the neonatal period. In early childhood it may present as chronic constipation with intermittent fecal soiling. It occurs predominantly in males and there is an increased family incidence. Surgical treatment is indicated, but the diagnosis is confirmed by a suction biopsy that can be easily performed without general anesthesia. The biopsy would reveal an absence of ganglion cells in the submucsal and myenteric plexuses. A stool culture (choice A) would be performed if one was entertaining a bacterial cause of gastroenteritis, especially in a hospitalized patient. However vomiting, diarrhea, and abdominal distention in a newborn are unlikely to be caused by gastroenteritis, especially in this case with a tight sphincter noted on rectal examination. A barium enema (choice C) may be indicated in suspected cases of Hirschsprung disease, but it is the biopsy that makes the diagnosis. The barium enema in this case of Hirschsprung disease revealed a dilated proximal bowel with evidence of a contracted distal rectum. An alpha1-antitrypsin level (choice D) would not be indicated in this case. It is obtained when one suspects an alpha1-antitrypsin deficiency. Affected infants would present with jaundice, acholic stools, and hepatomegaly. A serum TSH (choice E) would be performed if a newborn infant were thought to have hypothyroidism. In the U.S., most states have mandatory newborn screening for thyroid disease. Frequently, congenital hypothyroidism is asymptomatic, but it may present with symptoms of constipation, lethargy, poor feeding, mottling, and prolonged jaundice. The typical features in this case are more suggestive of Hirschsprung disease.
7) A 7-year-old boy presents to the physician’s office with a 3-week history of left-sided anterior cervical lymph node enlargement. The enlarged nodes are not tender to palpation. A few papules developed on the left forearm at the onset of lymphadenopathy. The boy has a kitten at home. Which of the following is the most likely organism causing lymphadenopathy in this child?
A. Actinomyces israelii
B. Bartonella henselae
C. Francisella tularensis
D. Mycobacterium tuberculosis
E. Staphylococcus aureus
Explanation:
The correct answer is
B.Bartonella henselae is the pathogen of cat-scratch disease, which is a very common cause of chronic lymphadenitis in children. It typically presents as an enlarging non-tender lymph node, often located in the cervical, axillary, or inguinal regions. After being scratched by a kitten, a papule develops at the scratch site. Affected lymph nodes draining the involved area become enlarged in 2 weeks. Other symptoms include low-grade fever, malaise, fatigue and nonspecific body aches. The diagnosis of cat-scratch disease is best made by a serological test, such as an indirect fluorescence antibody test for antibodies to
B. henselae. Usually, treatment is necessary only in severe systemic infection. Actinomyces israelii(choice A) rarely causes anterior cervical adenopathy. Francisella tularensis(choice C) is the pathogen for tularemia, which is characterized by an ulcerative lesion at the site of inoculation, with regional lymphadenopathy that is exquisitely tender. Mycobacterium tuberculosis (choice D) most often causes pulmonary disease. A skin purified protein derivative (PPD) test is usually positive. Staphylococcus aureus(choice E) causes acute lymphadenitis that is associated with fever and tender lymph nodes.
A 4-year-old boy is brought to the emergency department for a painful and swollen right forearm. He was bitten and scratched by a family cat 2 days ago in the affected area. His temperature is 39.6 C (103.2 F). The right forearm is erythematous, edematous, and tender to touch. Which of the following is the most appropriate antibiotic treatment for this patient?A. Ampicillin
B. Amoxicillin-clavulanate
C. Clindamycin
D. Tetracycline
E. Trimethoprim-sulfamethoxazole
Explanation:
The correct answer is
B. Animal bite is a common problem in pediatrics. In this case, the patient was bitten by a cat. To initiate appropriate antibiotic treatment, one needs to understand which organisms are most likely causing this infection. In a cat-bite wound, the most common organisms isolated are Pasteurella multocida and Staphylococcus aureus. Among the choices, amoxicillin-clavulanate is the only antibiotic that is effective against both organisms. P. multocida infection usually manifests within 24-48 hours following the bite or scratch as localized swelling, erythema, tenderness, and serous or sanguinopurulent discharge. Fever, chills, and lymphadenopathy can also occur. Complications include tenosynovitis, osteomyelitis, and septic arthritis. P. multocida is found in the oral flora of 70% to 90% of cats, 25% to 50% of dogs, and a variable percentage in other animals. S. aureus is a common pathogen for cellulitis. It is often found on the skin. In a severe case of animal bite, the pathogens are usually polymicrobial. Therefore, amoxicillin-clavulanate is the treatment of choice; 7-10 days therapy is usually sufficient. Ampicillin (choice A) is an effective treatment against P. multocida, but it has no effect on S. aureus. Clindamycin (choice C) is effective against most serotypes of S. aureus, but is ineffective against P. multocida. Tetracycline (choice D) is effective again P. multocida, but it should not be given to children younger than 8 years. Trimethoprim-sulfamethoxazole (choice E) is not adequate on its own. When combined with clindamycin, however, it is an alternative treatment if the patient is allergic to penicillin compounds.
9) A 14-year-old male presents with a complaint of soreness, and weakness in his legs for the past day that has slowly spread from his calves to his thighs. He now complains of weakness in his trunk and arms. On examination he appears tired and lays on the examining table. His temperature is 37 C (98.6 F), pulse is 48/min, and respirations are 22/min. Both of his legs are diffusely tender. Deep tendon reflexes are absent in the lower extremities, and sensation is greatly diminished. Which of the following studies is essential for this patient’s diagnosis?
A. Creatinine phosphokinase levels
B. Stool culture for Campylobacter jejuni
C. Motor nerve conduction test
D. Cerebrospinal fluid studies
E. Muscle biopsy
Explanation:
The correct answer is
B. Guillain-Barré syndrome (GBS) is a postinfectious polyneuropathy that causes demyelination of BOTH motor and occasionally, sensory nerves. It is classically an ascending paralysis. CSF studies are essential for diagnosis and reveal a protein level usually twice normal values but with normal amounts of white blood cells, normal glucose level and an absence of pleocytosis (elevated lymphocytes). Autonomic nervous system involvement can produce the bradycardia seen in this vignette. Creatinine phosphokinase levels (choice A) may be mildly elevated and sometimes are normal, but are not essential for diagnosis. Motor nerve conduction tests (choice C) would show decreased velocities, but are not specific for GBS. A muscle biopsy (choice D) is not indicated and can be normal in early stages. Late disease reveals denervation atrophy. Stool culture for Campylobacter jejuni(choice E), a well recognized infection associated with GBS, is again not essential for diagnosis. By the time the disease presents stool cultures are often negative.
10) A 14-year-old boy is hit by an automobile while walking across the street and is immediately taken to the emergency department. On arrival, he is conscious and complains of shortness of breath and chest pain. Physical examination reveals an ecchymotic area over his right chest and subcutaneous emphysema. Breath sounds are absent on the right side. His trachea is deviated to the left, and his right hemithorax is tympanic to percussion. Which of the following is the most appropriate initial step in management of this patient?
A. 12-lead ECG
B. CT of the chest
C. Plain radiography of the chest
D. Chest tube thoracostomy
E. Pericardiocentesis
Explanation:
The correct answer is
B. The findings on physical examination strongly suggest tension pneumothorax. This is a life-threatening emergency that needs to be managed immediately with either chest tube thoracostomy or needle thoracocentesis to relieve the tension on the affected side of the thorax. Physical examination reveals tachycardia, tachypnea, decreased or absent breath sounds over the involved hemithorax, increased resonance to percussion, subcutaneous emphysema, and deviation of the trachea to the opposite side. Tension pneumothorax develops when air leaking into the chest increases intrathoracic pressure, completely collapsing the lung on that side. It results in displacement of the mediastinum and trachea to the opposite side of the chest and impedes venous return. 12-lead ECG (choice A), CT of the chest (choice C), and plain radiography of the chest (choice E) may be indicated on a trauma patient after the patient is stabilized. In tension pneumothorax, no imaging study should precede the emergent relief of tension inside the chest. Pericardiocentesis (choice D) is indicated when there is cardiac tamponade, caused by build-up of fluid in the pericardium. Cardiac tamponade significantly affects ventricular relaxation and markedly decreases cardiac output.
Tags: Pediatrics
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