Hypotonia

Hypotonia, often referred to as floppy baby syndrome, is characterized by diminished muscle tone, which is the inherent resistance of muscles to passive stretching. It is crucial to distinguish between muscle tone and muscle strength, as the latter pertains to the capability of muscles to exert force actively. Though hypotonia manifests as a symptom, it is not an isolated medical disorder. Instead, it can signify various underlying diseases or conditions affecting either the motor nerve control from the brain or the muscle strength itself.

1 Signs and symptoms

1.1 Floppy baby syndrome

Infants with hypotonia may appear limp at birth, resembling a "rag doll". They may rest with their elbows and knees loosely extended, as opposed to the typical flexed position. The baby might also display difficulties with feeding, due to the associated muscle weaknesses.

1.2 Developmental delay

Hypotonia may hinder an infant's motor development milestones such as holding the head up, sitting without support, and walking. The delay is due to the diminished muscle strength associated with hypotonia.

1.3 Muscle tone vs. muscle strength

Muscle tone refers to the tension present in a muscle when it is passively stretched. In contrast, muscle strength refers to the active force a muscle produces when it contracts. Hypotonia is identified by a lack of resistance to passive stretching, whereas muscle weakness is recognized by impaired active movement.

2 Cause

Hypotonia may arise from various underlying causes, either from the central nervous system or the peripheral structures, including the spinal cord, peripheral nerves, and skeletal muscles.

Some conditions known to cause hypotonia include:

Congenital – i.e. disease a person is born with (including genetic disorders presenting within 6 months)

• Genetic disorders are the most common cause
  • 22q13 deletion syndrome a.k.a. Phelan–McDermid syndrome
  • 3-Methylcrotonyl-CoA carboxylase deficiency
  • Achondroplasia
  • Aicardi syndrome
  • Autism spectrum disorders
  • Canavan disease
  • Centronuclear myopathy (including myotubular myopathy)
  • Central core disease
  • CHARGE syndrome
  • Cohen syndrome
  • Costello syndrome
  • Dejerine–Sottas disease (HMSN Type III)
  • Down syndrome a.k.a. trisomy 21 — most common
  • Ehlers–Danlos syndrome
  • Familial dysautonomia (Riley–Day syndrome)
  • FG syndrome
  • Fragile X syndrome
  • Griscelli syndrome Type 1 (Elejalde syndrome)
  • Disorder Growth Hormone Disorder Pituitary Dwarfism
  • Holocarboxylase synthetase deficiency / Multiple carboxylase deficiency
  • Krabbe disease
  • Leigh's disease
  • Lesch–Nyhan syndrome
  • Marfan's syndrome
  • Menkes syndrome
  • Methylmalonic acidemia
  • Myotonic dystrophy
  • Niemann–Pick disease
  • Nonketotic hyperglycinemia (NKH) or Glycine encephalopathy (GCE)
  • Noonan syndrome
  • Neurofibromatosis
  • Patau syndrome a.k.a. trisomy 13
  • Prader–Willi syndrome
  • Rett syndrome
  • Septo-optic dysplasia (de Morsier syndrome)
  • Snyder–Robinson syndrome (SRS)
  • Spinal muscular atrophy (SMA)
  • Succinic semialdehyde dehydrogenase deficiency (SSADH)
  • Tay–Sachs disease
  • Werdnig–Hoffmann syndrome – Spinal muscular atrophy with congenital degeneration of anterior horns of spinal cord. Autosomal recessive
  • Wiedemann–Steiner syndrome
  • Williams syndrome
  • Zellweger syndrome a.k.a. cerebrohepatorenal syndrome
• Developmental disability
  • Cerebellar ataxia (congenital)
  • Sensory processing disorder
  • Developmental coordination disorder
  • Hypothyroidism (congenital)
  • Hypotonic cerebral palsy
  • Teratogenesis from in utero exposure to Benzodiazepines

Acquired

Acquired – i.e. onset occurs after birth

• Genetic
  • Muscular dystrophy (including Myotonic dystrophy) – most common
  • Metachromatic leukodystrophy
  • Rett syndrome
  • Spinal muscular atrophy
• Infections
  • Encephalitis
  • Guillain–Barré syndrome
  • Infant botulism
  • Meningitis
  • Poliomyelitis
  • Sepsis
• Toxins
  • Infantile acrodynia (childhood mercury poisoning)
• Autoimmunity disorders
  • Myasthenia gravis – most common
  • Abnormal vaccine reaction
  • Celiac disease
• Metabolic disorder
  • Hypervitaminosis
  • Kernicterus
  • Rickets
• Neurological
  • Traumatic brain injury, such as the damage that is caused by shaken baby syndrome
  • Lower motor neuron lesions
  • Upper motor neuron lesions
• Miscellaneous
  • Central nervous system dysfunction, including cerebellar lesions and cerebral palsy
  • Hypothyroidism
  • Sandifer syndrome
  • Neonatal benzodiazepine withdrawal syndrome in children born to mothers treated in late pregnancy with benzodiazepine medications.

3 Diagnosis

Early detection of hypotonia is generally straightforward, especially in infancy. However, pinpointing the root cause can be intricate and sometimes remains undetermined.

3.1 Terminology

• Central Hypotonia: Originates from issues within the central nervous system.
• Peripheral Hypotonia: Associated with complications within the spinal cord, peripheral nerves, or skeletal muscles.

On a clinical examination, there is noticeable reduced resistance to passive movements. The muscles might feel unusually soft to touch. Additionally, diminished deep tendon reflexes might be present.

Treatment and Management

The primary management for hypotonia stemming from idiopathic or neurologic causes includes:

• Physical Therapy: To improve muscle strength and coordination.
• Occupational Therapy: Aims to enhance fine motor skills and daily living activities.
• Music Therapy: Can stimulate muscle movement and coordination through rhythm and melodies.

Early intervention is paramount, as it can significantly improve the prognosis and quality of life for those with hypotonia.

Summary

Hypotonia is associated with disruptions in the input from stretch receptors or potential abnormalities in the cerebellum's facilitatory influence on the fusimotor system. This system is responsible for controlling muscle spindle sensitivity. While the condition may pose challenges, with timely diagnosis, intervention, and appropriate therapies, individuals with hypotonia can lead productive lives.

External links

• hypotonia at NINDS

• Hypotonia – Medline Plus

References

Hypotonia Resources
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