SPEX Exam Pediatrics 6

Question 1

A 3-year-old presents with recurrent episodes of painless rectal bleeding. Colonoscopy reveals a polyp in the descending colon. Histology shows a hamartomatous polyp with smooth muscle extending into the lamina propria. The child's father had similar polyps removed in childhood. Which syndrome is most likely, and what is the most important long-term concern?

Accepted Answer

Juvenile polyposis syndrome; risk of colorectal cancer by the 4th decade

Answer

The histology described — hamartomatous polyp with smooth muscle in the lamina propria — is characteristic of juvenile polyps. When multiple juvenile polyps occur with a family history, juvenile polyposis syndrome (JPS) is the diagnosis. JPS carries a significant cumulative risk of colorectal cancer (estimated 39–68% lifetime risk) by the 3rd–4th decade, distinguishing it from solitary juvenile polyps which are benign. Peutz-Jeghers polyps have a distinctive arborizing smooth muscle pattern, and FAP involves adenomatous (not hamartomatous) polyps.

Question 2

A 7-year-old boy with a known seizure disorder is brought in after his mother noticed he has been having 'staring spells' lasting 10–30 seconds with subtle lip smacking but no post-ictal confusion. His EEG shows focal slowing over the right temporal region with sharp waves. His current medication is ethosuximide. What is the most appropriate next step?

Accepted Answer

Switch to oxcarbazepine or carbamazepine as this presentation suggests focal onset impaired awareness seizures

Answer

The clinical features — focal temporal EEG changes, automatisms (lip smacking), and absence of post-ictal confusion — are characteristic of focal onset impaired awareness seizures (formerly complex partial seizures), not typical absence seizures. Ethosuximide is effective only for typical absence seizures (generalized, 3 Hz spike-and-wave on EEG, no automatisms, no focal EEG changes) and has no role in focal epilepsy. Oxcarbazepine or carbamazepine are first-line agents for focal seizures in children. An MRI is also warranted to exclude a structural lesion, but switching the antiepileptic is the most critical next step.

Question 3

A 14-year-old female presents with primary amenorrhea. Physical exam reveals normal breast development (Tanner III), absent pubic hair, and a blind-ending vaginal pouch. Karyotype returns 46,XY. Serum testosterone is in the normal male range. Which finding best explains this patient's phenotype?

Accepted Answer

Complete androgen insensitivity syndrome due to a defect in the androgen receptor gene

Answer

This is classic Complete Androgen Insensitivity Syndrome (CAIS): 46,XY karyotype, phenotypically female, normal breast development (from aromatization of testosterone to estrogen), absent pubic/axillary hair (androgens cannot act on hair follicles), blind-ending vaginal pouch, and male-range testosterone. The androgen receptor is non-functional, so despite normal testosterone production, the body cannot respond to androgens. In 5-alpha reductase deficiency, patients typically have ambiguous genitalia at birth and virilize at puberty. MRKH is always 46,XX. 17-alpha hydroxylase deficiency would result in low testosterone and hypertension.

Question 4

A 2-week-old neonate born at 36 weeks gestation presents with bilious vomiting, abdominal distension, and failure to pass meconium within the first 48 hours. Abdominal X-ray shows a 'ground glass' appearance in the right lower quadrant without air-fluid levels. Which diagnosis and associated genetic condition should be highest on the differential?

Accepted Answer

Meconium ileus; strongly associated with cystic fibrosis (CFTR mutations)

Answer

The 'ground glass' appearance in the right lower quadrant on X-ray (representing inspissated meconium mixed with air) without air-fluid levels is the classic radiographic sign of meconium ileus. Meconium ileus is the presenting feature in approximately 15–20% of cystic fibrosis cases in neonates, and 90% of meconium ileus cases are caused by CF. Hirschsprung disease presents with failure to pass meconium but without the ground-glass sign, and X-ray typically shows dilated loops. Duodenal atresia shows the 'double bubble' sign. Bilious vomiting with the ground-glass pattern in a premature infant points directly to meconium ileus.

Question 5

A 9-year-old boy presents with a 3-week history of bone pain in the right distal femur, low-grade fever, and a 4 cm soft tissue mass. MRI shows a destructive metaphyseal lesion with periosteal elevation (Codman triangle) and extension into surrounding soft tissue. Biopsy reveals small round blue cells arranged in sheets with Homer-Wright rosettes. Which translocation is most characteristically associated with this tumor?

Accepted Answer

t(11;22)(q24;q12) involving EWS-FLI1 fusion

Answer

Homer-Wright rosettes in a small round blue cell tumor of bone with Codman triangle periosteal reaction in a child is classic for Ewing sarcoma. The t(11;22)(q24;q12) translocation creating the EWS-FLI1 fusion protein is found in approximately 85% of Ewing sarcoma cases and is the hallmark genetic abnormality. The SS18-SSX fusion is characteristic of synovial sarcoma; PAX3-FOXO1 is seen in alveolar rhabdomyosarcoma; FUS-DDIT3 is associated with myxoid liposarcoma. The combination of location (metaphysis), age (school-age child), and rosette histology narrows this specifically to Ewing sarcoma.

SPEX Exam Practice Test

SPEX Exam Practice Test

SPEX Exam Pediatrics 6