By Dr Ananya Mandal, MD
Hypotonia results in loss of normal resting muscle tone. It is basically a symptom of some underlying disease.
The condition is manifested as reduced resistance to passive movement of joints.
Sources of hypotonia
The defect may lie at the –
- Central nervous system
Central hypotonia with defects at the brain or spinal cord
- Peripheral nerves (motor and/or sensory)
Peripheral hypotonia that may affect any place between the spinal cord and muscle.
Neuromuscular junction at the connection between the nerve endings and the muscles may be affected.
The nerves bring in the impulse from the central nervous system that makes the muscle maintain contraction or a resting muscle tone. Defects may lie at the level of the muscles.
Types of hypotonia
Hypotonia may be seen at birth or later. At birth it is termed congenital hypotonia and it seen later it is called acquired hypotonia.
Causes of hypotonia
There are several causes of hypotonia, these include genetic conditions, nutritional causes and so forth. (1-4)
Genetic causes of hypotonia
There are several genetic causes of hypotonia, these include:
- Down Syndrome – This is a genetic disease with a chromosomal abnormality where the 21st pair of chromosome has an extra chromosome. This leads to heart defects, mental retardations and other neurological complications.
- Prader-Willi syndrome is a rare genetic disease that causes restricted growth and learning difficulties
- Tay-Sachs disease is another rare and fatal genetic disorder that causes progressive damage to the nervous system.
- Williams Syndrome – is a rare genetic condition that causes defects in development, co-ordination and language.
- Spinal muscular atrophy is an inherited disease that leads to muscle weakness and a progressive loss of movements.
- Charcot-Marie-Tooth disease is yet another inherited condition that affects the myelin covering of nerves. Myelin forms a protective covering over all major nerves of the body.
- Connective tissue disorders include Marfan’s syndrome and Elher-Danlos syndrome. These are inherited and lead to defects in connective tissues which provide support to other tissue and organs.
Nutritional causes of hypotonia
Some causes of hypotonia are a result of malnutrition, these include:
- Rickets – This is caused by vitamin D deficiency
- Malnutrition – Malnutrition in the mother as well as the baby or child especially with lack of adequate protein in diet may lead to hypotonia
Causes of hypotonia that involve the brain
Some of the causes of hypotonia involve the brain. These include:
- Brain and spinal cord injury that may include bleeding into the brain
- Serious infections of the brain and its parts like meningitis or encephalitis
- Kernicterus – This condition is severe affliction of the brain of the new born with bilirubin from the jaundice right after birth. It may lead to severe neurological deficits, retardation, seizures and hypotonia or hypertonia (increased muscle tone).
Causes of hypotonia at birth
- Prematurity – Babies born prematurely carry a risk of being born hypotonic. The condition often resolves as the baby grows
- Hypothyroidism – Lack of thyroid hormone at birth may lead to hypotonia. If severe it may manifest later as Cretinism characterized by coarse facial features, mental retardation etc.
- Sepsis – Severe infection in the new born
Other causes of hypotonia
Other causes of hypotonia include:
Edited by April Cashin-Garbutt, BA Hons (Cantab)
What is hypotonia?