Transcript Hypotonia

Pediatric Neurology Quick Talks
Hypotonia
Michael Babcock
Summer 2013
Scenario
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2 do M in the NICU
Poor feeding and “weakness”
Not intubated
Delivered 37 weeks by C/S – failure to progress
Poor maternal pre-natal care
HC ~50%
Exam – axillary slippage, reduced spontaneous movements, +head lag,
normal suck. +awake
Hypotonia – Localize –> Central or Peripheral
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Central (brain/spinal cord)
– Normal/mild weakness
– normal bulk
– normal/increased reflexes
– Dysmorphisms
– encephalopathy
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Peripheral (Anterior horn,
peripheral nerve, NMJ, muscle)
– Marked weakness
– decreased bulk
– decreased reflexes
– no dysmorphisms
– Awake, alert
Central Causes
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Sepsis
Maternal narcotics
Hypothyroid
Prematurity
HIE
Down's Syndrome
Prader-Willi
Inborn Errors of Metabolism
– Zellweger
Cerebral dysgenesis
Peripheral Causes
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Anterior Horn
– SMA
– Pompe
Peripheral Nerve (uncommon)
– Inflammatory – GBS
– Demyelinating
– Axonal
– Metabolic- Leigh
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Neuromuscular Junction
– Myasthenias
– Infantile botulism
– Hypermagnesemia
Muscle
– Myopathy
– Muscular dystrophy
– Myotonic dystrophy
– Metabolic myopathy
Perkowski's top 5 not to miss causes of floppy baby
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Down's syndrome
Prader Willi
Pompe (have heart problems)
Zellweger
Spinal Muscular Atrophy
However, most common is HIE
History
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Mother – systemic illness, fever, substance abuse
Pregnancy – polyhydramnios, fetal movement, abnormal lie
Delivery – complicated/prolonged, trauma, Apgars
Family history – delayed milestones, weakness, myotonia
Exam – Assess Tone
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Tone is resistance to stretch forces, develops with nervous system
development, low tone is normal for premature infants – Ballard testing.
Resting posture – assess resting posture when infant is quiet/drowsy
– Hypotonic infant – frog leg position
– Long-standing immobility can cause joint contractures –
arthrogryposis
Passive manipulation
– Infants develop increasing flexor tone in extremities – causes
increased recoil after limb is extended
– Head control in vertical/horizontal suspension
– Vertical suspension
Ballard Testing – Testing tone
Work Up
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Central
– Electrolytes (Mg, Ca, Gluc)
– TFT's
– Brain imaging – U/S vs MRI
– EEG
– Karyotype, CMA
– Metabolic work-up
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Peripheral
– CK
– EMG/NCS
– muscle/nerve bx
Spinal Muscular Atrophy (SMA)
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AR – SMN1 gene – SMN protein
(survival motor neuron); SMN2
gene regulates severity
Weakness and atrophy of
muscles, including tongue
Symmetric weakness, more
proximal than distal, more severe
in LE
Tongue fasciculations
Absent DTRs
Normal intellectual capacity
Facial muscles typically spared
early on
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Types
– Type 1 – infantile - Werdnig
Hoffman - <6mo. - never sit
– Type 2 – intermediate Dubowitz – 6-18 months –
never walk
– Type 3 – juvenile Kugelberg-Welander –
18mo- 17 years. - able to
walk initially, often lose this.
– Type 4 – adult-onset
Myasthenias
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Congenital
– Genetic disorder of NMJ
– Hypotonia, weakness (ocular, bulbar, respiratory)
• Variable onset, sometimes in utero – arthrogryposis
– Recurrent ALTEs
– Fatigability, weak cry, feeding difficulties, episodic apnea
– Sometimes respond to AchE inhibitors
Transient neonatal
– Transplacental transfer of AchR Antibodies.
– 10-15% of infant of myasthenic mothers
– Hypotonia, weakness—bulbar and respiratory, within 4 days of birth
– Good response to AchE inhibitors
Infant Botulism
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Weakness and hypotonia
Can have hx of honey ingestion; though contamination from soil is most
common
Constipation is often first sign
Eye findings, ophthalmoplegia – botulism is descending paralysis
Can test stool
Can give Human boutlinum immunoglobulin – 50mg/kg in first few days
shortens course
Often severe respiratory weakness requiring ventilation, prolonged course.
Prep Question
During the health supervision visit for a 6 week old boy, his father expresses concern
that his son “doesn’t look like” his other children. Growth parameters are normal
except for a head circumference of 35.5 cm (<5th percentile).
On PE, you note that the infant does not appear to fixate or track your face visually.
There is a “slip through” on vertical suspension and “draping over” on horizontal
suspension. DTRs are brisk. Moro reflex is present and brisk. Of the following, the
MOST likely cause of this infants hypotonia is:
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Anterior horn cell disease
Congenital brain malformation
Congenital myasthenic syndrome
Congenital myopathy
Spinal cord disease
B. Congenital brain malformation
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Hypotonia
– Localize! UMN vs. LMN signs, axial vs appendicular
– Take into account growth parameters, especially HC, as well as
features such as tracking
Regarding other choices:
– A. anterior horn cell disease – wouldn't cause microcephaly or
increased reflexes
– C. Congenital myasthenic syndrome – wouldn't cause microcephaly or
brisk reflexes
– D. Congenital myopathy – no microcephaly or poor visual tracking
– E. Spinal cord disease – wouldn't cause microcephaly or poor visual
tracking.
References
Paediatr Child Health. 2005 September; 10(7): 397–400.; PMCID: PMC2722561; A schematic approach to hypotonia
in infancy
Respiratory update.com