Paeds Vivas · fetal-neonatal-and-perinatal
Neonatal hypotonia and neuromuscular weakness — branching viva
Branching viva from the central/peripheral bedside split, through the weak areflexic infant and the floppy baby of an affected mother, to the timing and evidence of disease-modifying therapy for spinal muscular atrophy.
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Study tools
Target exams
RACP General PaediatricsRACP DCEMRCPCH ClinicalRCPSC Pediatrics
Prompt
You are the neonatal registrar in the postnatal and neonatal unit. The midwife asks you to review three hypotonic neonates of differing cause: a floppy-but-strong dysmorphic infant, a weak areflexic alert infant, and a floppy neonate of a mother with mild myotonia. The examiner releases information in stages.
Station opening
Examiner: "Define hypotonia and tell me why the first decision in a floppy neonate is whether the baby is also weak." [10]
Strong candidate (must-hit)
- Defines hypotonia as reduced resistance to passive movement (a loss of postural tone), distinct from weakness (a loss of active force); explains that the central/peripheral split turns on whether strength and reflexes are preserved — a central lesion lowers tone but keeps the motor unit intact, while a peripheral (motor-unit) lesion lowers tone, strength and reflexes together while sparing alertness. [10]
Weak candidate
- "Hypotonia is low muscle tone, usually from a muscle problem." [10]
References6ShowHide
- [1]Finkel RS; Mercuri E; Darras BT; Connolly AM; et al Nusinersen versus Sham Control in Infantile-Onset Spinal Muscular Atrophy. N Engl J Med, 2017.PMID 29091570
- [2]Strauss KA; Farrar MA; Muntoni F; Saito K; et al Onasemnene abeparvovec for presymptomatic infants with three copies of SMN2 at risk for spinal muscular atrophy: the Phase III SPR1NT trial. Nat Med, 2022.PMID 35715567
- [3]Mercuri E; Finkel RS; Muntoni F; Wirth B; et al Diagnosis and management of spinal muscular atrophy: Part 1: Recommendations for diagnosis, rehabilitation, orthopedic and nutritional care. Neuromuscul Disord, 2018.PMID 29290580
- [5]Glascock J; Sampson J; Haidet-Phillips A; Connolly A; et al Treatment Algorithm for Infants Diagnosed with Spinal Muscular Atrophy through Newborn Screening. J Neuromuscul Dis, 2018.PMID 29614695
- [9]Ostojić S; Kovačević G; Meola G; Pešović J; et al Main features and disease outcome of congenital myotonic dystrophy - experience from a single tertiary center. Neuromuscul Disord, 2024.PMID 38810326
- [10]Bodensteiner JB The evaluation of the hypotonic infant. Semin Pediatr Neurol, 2008.PMID 18342256