Hypotonia

Hypotonia

Definition And Initial Evaluation

What is hypotonia?

• Diminished resistance Of muscles to passive stretching.
• Hypotonia is a state of low muscle resistance to movement 2nd.

Hypotonia vs. Weakness (1st step)

• Is the patient hypotonic?
• Is the patient weak?
• Weakness Is a decreased ability to voluntarily and actively move muscles.
• Relationship: Hypotonia can be associated with weakness, but in some cases is present with normal motor strength.

Muscle tone types:

• Phasic tone (Appendicular structures).
• Postural tone (Axial structures).
• Note: There may be a discrepancy between phasic tone and postural tone in a given patient.

Control of the muscles tone:

• Supraspinal influences: Inputs from the central nervous system.
  • (Inhibitors)
  • -(Facilitator)
• Motor unit Or segmental structures related.

Differential Anatomic Diagnosis

Try to localize the process within the nervous system:

• Brain
• Spinal cord
• Anterior horn cell
• Peripheral nerve
• Neuromuscular junction
• Muscle fiber

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Assessment Of The Hypotonic Child

History

The usual referral of a hypotonic infant usually occurs in 2 different situations:

1. To evaluate the “Floppy infant”.
2. Concern about the Developmental progress Of the infant.
   • Define the type of developmental delay:
     • Motor developmental delay.
     • Motor and cognitive delay.
     • Global delay including motor delay.

Key historical elements:

• Antenatal
• Neonatal
• The onset Of the hypotonia is also important as it may distinguish between congenital and acquired etiologies.
• Feeding
• Respiratory problems
• Voice
• Sleep
• Developmental history
• Constipation / diarrhea
• Chronic disease / systemic diseases
• Family history
• Social history

Physical Examination

General examination:

• Alertness
• Dysmorphic features
• Growth parameters
• Breathing pattern
• Ability to cough And the cough character.
• Character of the cry
• Posture (Flaccid, Frog position).
• Spontaneous movements (E.G. Antigravity).
• Deformities and contractures
• Dislocation of the hip

• Frog Position (1st)
• Arthrogryposis dislocation of the hips (2nd)
• Scissoring posture In cerebral palsy. (3rd)

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Systems exam:

• Skin
• Chest: Respiratory irregularities/failure.
• Cardiovascular: Cardiac failure.
• Abdomen: Organomegaly.
• Abnormalities of genitalia

Neurological examination:

• Cranial nerves:

  • Extra-ocular muscles
  • Ptosis
  • Vision
  • Fundus
  • Facial muscles
  • Tongue
  • Swallowing
  • Hearing

• Motor examination:

  • Muscles bulk
  • Muscle tone
  • Muscle power
  • Muscle stretch reflex (DTR ↑ ↑ ↑)
  • Abnormal movement

• Primitive reflexes:

  • Tonic neck reflex
  • Grasp reflex
  • Step reflex
  • Crawl reflex
  • Note: Persistent primitive reflexes are characteristic of central hypotonia.

• Sensation

• Hypotonia-focused examination

Localization Groups

Localization into 2 large groups:

1. The supraspinal conditions: Cerebral or central hypotonia (about 2/3).

   • Traction response (“Head lag”).
   • Vertical suspension (“Slips through”).
   • Horizontal suspension (“Drapes over”).

2. Segmental conditions: Motor unit hypotonia or lower motor unit or peripheral hypotonia (about 1/3).

   • Passive manipulation Of the limbs.

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Central Vs. Peripheral Hypotonia

Central (Cerebral) Hypotonia

Clinical features:

• Hypotonia
• Obtundation
• Seizures
• DTR ↑ ↑ ↑ (Normal or brisk, clonus, Babinski sign).
• Persistent primitive reflexes.
• Extensor plantar response.
• Suboptimal head growth (Microcephaly).
• Axial weakness A significant feature; weakness less than degree of hypotonia.
• Dysmorphic features.
• Malformation of other organs.
• Global developmental delay.
• Movement through postural reflexes (Neck righting reflex 3m, the Landau reflex 3-24m).

Etiologies & history:

• History consistent with a CNS insult.
• Systemic diseases: Influences the entire CNS diffusely to cause hypotonia.
• Syndromic / nonsyndromic central hypotonia.
• Cerebral dysgenesis.
• Grossly normal brain: ☑ With delayed myelination, ☑ with normal myelination.
• Chromosomal disorder.
• Birth trauma, HIE, infections.

Diagnostic clues:

Lower Motor Unit (Peripheral / Motor Unit) Hypotonia

Clinical features:

• Hypotonia
• Alert expression.
• Weakness: Convincing weakness; decreased antigravity limb movements.
• Areflexia: Absence of reflexes (muscle stretch reflex).
• Weak cry and suck.
• Tongue fasciculation.
• External ophthalmoplegia.
• Arthrogryphosis.
• Positive Gower sign.
• No abnormalities of other organs.
• No global delay: Delayed gross motor development.
• Muscle fasciculations.
• Failure of movement on postural ri.
• Abnormal size and/or texture/consistency Of the muscle on observation and palpation.

Diagnostic clues:

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Specific Disorders

Spinal Muscular Atrophy (SMA)

Overview:

• Characterized by Degeneration of the anterior horn cells In the spinal cord and motor nuclei in the lower brainstem, which result progressive muscle weakness and atrophy.
• Autosomal recessive. 1 per 10,000 live births. Carrier frequency 1:100.
• Cognition is unaffected.
• SMA have diffuse symmetric proximal muscle weakness That is greater in the lower than upper limbs, and absent or markedly decreased deep tendon reflexes.
• SMA is associated with a restrictive, progressive respiratory insufficiency, Particularly SMA type 0 and type 1.
• Sleep disturbances and CHD May accompany SMA type 0.

SMA type 0 (prenatal onset) and SMA type 1 (infantile onset) are the most common and severe types. (Total 5 types).

SMA type 1 / infantile spinal muscular atrophy / Werdnig-Hoffmann disease:

• Age of onset from birth-6 month.
• Severe, symmetric flaccid paralysis.
• Absent deep tendon reflexes.
• Never achieve the ability to sit unsupported.
• Upper cranial nerves are spared, Have an alert expression, furrowed brow, and normal eye movements.
• Weakness of the bulbar muscles Results in a weak cry, poor suck and swallow reflexes, pooling of secretions, tongue fasciculations.
• Respiratory muscle weakness Leads to progressive respiratory failure.
• Life expectancy less than 2 year.

Management:

• Molecular genetic testing / EMG and muscle biopsy For diagnosis.
• Supportive therapy Is directed at providing nutrition and respiratory assistance as needed and treating or preventing complications of weakness e.G spinal bracing.
• Disease-modifying therapy (DMT) With Nusinersen n, Onasemnogene Abeparvovec, And Risdiplam.
• Gene replacement therapy.

Other Motor Unit Disorders

Anterior horn cell:

• Spinal muscular atrophy
• Poliomyelitis

Nerve fibre: Neuropathies (demyelinating or axonal):

• Acquired: Guillain-Barré syndrome.
• Infectious: Diphtheria, syphilis, coxsackie, HIV.
• Toxic: Drugs, heavy metals.
• Nutritional: Vit b-, b-, b-1, e, folate.
• Endocrine: Diabetes, uraemia.
• Metabolic neurodegenerative causes.
• Hereditary: Charcot-Marie-Tooth disease.

Neuromuscular junction:

• Myasthenia gravis
• Botulism

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Muscle disorders:

• Dystrophinopathies (Lack of specific muscle protein): Duchenne, becker’s fascioscapular humeral, limb girdle and congenital muscular dystrophies.
• Congenital myopathies (Abnormal muscle structure).
• Muscle membrane disorders: Congenital myotonias, congenital myotonic dystrophies.
• Inflammatory myopathies: Dermatomyositis, poliomyositis.
• Metabolic myopathies: Lipid glycogen storage diseases.
• Endocrine myopathies: Hypothyroidism.
• Energy depletion within muscle: Mitochondrial, free-fatty acid oxidation and carnitine disorders.
• Muscular dystrophy.
• Spinal muscular atrophy.
• Myasthenia gravis.
• Congenital myotonia.

Systemic Diseases:

• Sepsis
• Congenital heart disease
• Hypothyroidism
• Rickets
• Malabsorption, malnutrition
• Renal tubular acidosis

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Diagnostic Workup For Hypotonia

Investigations

• Laboratory (CK, aldolase, LDH & aminotransferases)
• Electrophysiologic studies — Nerve conduction and EMG
• Magnetic resonance imaging
• Muscle biopsy
• Genetic testing

Targeted investigations table:

Assessment	investigation	potential diagnosis
Targeted investigations	CT/MRI infections screen EEG	birth trauma HIE cerebral dysgenesis infections
Multi disciplinary assessment	Genetic studies (karyotyping FISH methylation studies mutation analysis)	chromosomal or genetic problems
Creatinine kinase EMG/ NCS	Muscle biopsy	chromosomal or genetic problems
	Direct mutation study	congenital muscles, nerves, neuromuscular disorders

Clinical clues on neurological examination:

NCS/EMG:

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