PLAB 1 Paediatrics 2 — Questions and Answers
Question 1: A newborn infant is found to have bilateral undescended testes and ambiguous genitalia. What is the most important initial investigation?
- Testicular ultrasound
- Urgent serum 17-hydroxyprogesterone level to exclude congenital adrenal hyperplasia (CAH) (Correct answer)
- Chromosomal analysis only
- Reassure parents and arrange outpatient follow-up
Correct answer: Urgent serum 17-hydroxyprogesterone level to exclude congenital adrenal hyperplasia (CAH)
Bilateral undescended testes with ambiguous genitalia requires urgent investigation for congenital adrenal hyperplasia (CAH), which can cause a life-threatening salt-wasting crisis. Serum 17-hydroxyprogesterone is the key initial test. Electrolytes should also be checked urgently as hyponatraemia and hyperkalaemia can be fatal.
Question 2: A 7-year-old child presents with periorbital oedema, generalised oedema, and frothy urine. Urine dipstick shows 4+ protein. Blood tests show low serum albumin (15 g/L) and high cholesterol. What is the most likely diagnosis?
- Acute glomerulonephritis
- Nephrotic syndrome (Correct answer)
- Urinary tract infection
- Haemolytic uraemic syndrome
Correct answer: Nephrotic syndrome
The triad of nephrotic syndrome is heavy proteinuria (>3.5 g/day), hypoalbuminaemia, and oedema. Hypercholesterolaemia is also characteristic. In children, the most common cause is minimal change disease. First-line treatment is oral corticosteroids (prednisolone), with >90% responding.
Question 3: A 10-year-old child presents 2 weeks after a sore throat with haematuria, facial oedema, hypertension, and dark ('cola-coloured') urine. What is the most likely diagnosis?
- Nephrotic syndrome
- Post-streptococcal glomerulonephritis (Correct answer)
- IgA nephropathy
- Wilms' tumour
Correct answer: Post-streptococcal glomerulonephritis
Post-streptococcal glomerulonephritis typically presents 1-3 weeks after a Group A streptococcal pharyngitis or skin infection. Features include haematuria (cola-coloured urine), hypertension, oedema, and reduced urine output. Anti-streptolysin O (ASO) titre is elevated and complement C3 is low.
Question 4: A 3-year-old child presents to A&E with a non-blanching purpuric rash, fever, and altered consciousness. What is the most important immediate action?
- Take blood cultures before doing anything else
- Administer IV/IM benzylpenicillin or ceftriaxone immediately without waiting for investigation results (Correct answer)
- Request an urgent CT head
- Apply EMLA cream and obtain IV access before treatment
Correct answer: Administer IV/IM benzylpenicillin or ceftriaxone immediately without waiting for investigation results
A non-blanching purpuric rash with fever and altered consciousness strongly suggests meningococcal septicaemia. This is a medical emergency — antibiotics (IV ceftriaxone or benzylpenicillin) must be given immediately. Do not delay treatment for investigations. Blood cultures can be taken alongside but must not delay antibiotics.
Question 5: According to UK guidelines, at what age should a child be referred for further assessment if they are not walking independently?
- 12 months
- 15 months
- 18 months (Correct answer)
- 24 months
Correct answer: 18 months
While most children walk independently between 12-15 months, the threshold for referral for developmental assessment is 18 months if a child is not walking independently. This may indicate developmental delay, neurological conditions (e.g., cerebral palsy), or other causes requiring investigation.
Question 6: A 5-year-old child presents with a widespread erythematous rash that started on the face ('slapped cheek' appearance) and has spread to the trunk and limbs in a lace-like pattern. What is the causative organism?
- Measles virus
- Parvovirus B19 (Correct answer)
- Human herpesvirus 6
- Group A Streptococcus
Correct answer: Parvovirus B19
Parvovirus B19 causes erythema infectiosum (fifth disease/slapped cheek syndrome). The characteristic 'slapped cheek' facial rash is followed by a lace-like reticular rash on the trunk and limbs. The child is no longer infectious once the rash appears. It can cause aplastic crisis in sickle cell disease and hydrops fetalis in pregnancy.
PLAB 1 Paediatrics 2
A newborn infant is found to have bilateral undescended testes and ambiguous genitalia.
What is the most important initial investigation?