SPEX Exam Pediatrics 4

Question 1

A 3-week-old male infant presents with projectile vomiting after feeds, persistent hunger, and a palpable olive-shaped mass in the epigastrium. Electrolytes reveal Na+ 132, K+ 3.0, Cl- 88, HCO3- 30. Which metabolic derangement is most accurately described, and what is the FIRST step in management?

Accepted Answer

Hypochloremic hypokalemic metabolic alkalosis; IV fluid resuscitation before surgery

Answer

Pyloric stenosis causes hypochloremic, hypokalemic metabolic alkalosis due to repeated loss of gastric HCl. Surgery (Ramstedt pyloromyotomy) is definitive, but it is NOT an emergency — the metabolic alkalosis and dehydration must be corrected with IV normal saline (with KCl after urine output established) BEFORE the OR, as alkalosis increases anesthetic risk.

Question 2

A 7-year-old boy is brought in for enuresis. He has been dry during the day since age 3 but has never achieved consistent nighttime dryness. He has no dysuria, normal urinalysis, and no daytime urgency. His father reports he also wet the bed until age 10. Which statement BEST characterizes the appropriate management?

Accepted Answer

Reassure that primary monosymptomatic nocturnal enuresis is developmental; motivational therapy and enuresis alarm are first-line

Answer

This is primary monosymptomatic nocturnal enuresis (PMNE) — never dry at night, no daytime symptoms, normal UA. It has a strong genetic basis (autosomal dominant tendency). Management starts with reassurance, elimination of bladder irritants, and behavioral strategies. The enuresis alarm has the highest long-term cure rate. Desmopressin is useful for short-term situations (sleepovers) but not first-line for long-term resolution. Anticholinergics are for daytime urgency/incontinence, not PMNE. VCUG is not indicated without daytime symptoms or UTIs.

Question 3

A 14-month-old presents with a 4-day history of fever to 40°C, irritability, and refusal to walk. Exam shows warmth and limited range of motion of the right hip. WBC is 18,000, ESR 68, CRP 4.2 mg/dL. Hip ultrasound shows a joint effusion. Which combination of findings most strongly indicates septic arthritis over transient synovitis, guiding emergent surgical drainage?

Accepted Answer

ESR >40 AND WBC >12,000 AND refusal to bear weight AND fever >38.5°C (Kocher criteria)

Answer

The Kocher criteria (fever >38.5°C, ESR >40 mm/hr, WBC >12,000, non-weight-bearing) are used to stratify risk of septic arthritis vs. transient synovitis. With all 4 criteria present, predicted probability approaches 99%. This child meets all four, mandating emergent surgical irrigation and debridement — delay risks avascular necrosis of the femoral head. CRP >2.0 is used as a modification to Kocher but is not standalone. Ultrasound confirms effusion but cannot distinguish septic from transient synovitis.

Question 4

You are evaluating a 6-week-old with poor feeding, hypotonia, and a systolic murmur. Chest X-ray shows cardiomegaly with increased pulmonary vascular markings. Echo confirms a large VSD with left-to-right shunting. The infant is in moderate heart failure. Which pathophysiologic principle explains why cyanosis is typically ABSENT in isolated large VSD at this age?

Accepted Answer

Pulmonary vascular resistance remains elevated in early infancy, limiting the left-to-right shunt magnitude

Answer

At birth, pulmonary vascular resistance (PVR) is high and falls over the first weeks of life. In the immediate neonatal period, elevated PVR limits the magnitude of left-to-right shunting through the VSD — so symptoms of heart failure and pulmonary overcirculation develop only as PVR drops (typically by 4-8 weeks). Cyanosis is absent because blood flows left-to-right (oxygenated to pulmonary circulation), not right-to-left. This also explains why large VSDs may not become symptomatic at birth. Eisenmenger physiology (reversal to right-to-left shunt with cyanosis) is a late, irreversible complication of unrepaired defects.

Question 5

A 10-year-old girl presents with 3 months of joint pain, a malar rash worsened by sun exposure, oral ulcers, and fatigue. Labs: ANA 1:640 (homogeneous pattern), anti-dsDNA positive, C3 and C4 low, urinalysis shows 2+ protein and RBCs. Creatinine is 1.4 mg/dL (elevated for age). Which finding is the MOST important driver of the next management decision?

Accepted Answer

Evidence of renal involvement (proteinuria, hematuria, elevated creatinine) necessitating kidney biopsy to classify lupus nephritis

Answer

This child meets SLE criteria, but the critical next step is kidney biopsy. Renal involvement is present (proteinuria, hematuria, impaired creatinine for age), and lupus nephritis class (I-VI by ISN/RPS classification) determines induction therapy — Class III/IV requires aggressive immunosuppression (cyclophosphamide or mycophenolate + steroids), while Class V (membranous) has a different approach. Low complements and positive anti-dsDNA confirm activity but do not replace histology in guiding treatment. Initiating mycophenolate without biopsy risks undertreating proliferative nephritis.

SPEX Exam Practice Test

SPEX Exam Practice Test

SPEX Exam Pediatrics 4