Hypotonia literally means loss of muscle tone. The condition was first described in 1956 among infants who were termed “floppy infants”.
In healthy muscles some amount of stiffness or tension is always maintained even at rest. This can be assessed clinically as tone of the muscle.
Tone of the abdominal muscles for example hold in the abdominal contents and that of the back keep the back straight and allow walking, standing etc.
Tone reduces during sleep. If a person dozes off, usually this lack of tone leads them to slump.
Hypotonia is a diseased condition that results in rubbery limbs that are unable to hold themselves up. (1-4)
Symptoms of hypotonia
At first sight, the infants have an accentuation of their spinal curve, protrusion of their abdomen (due to lack of abdominal muscle tone).
On walking, the sufferers are seen to have flat feet, walking tip-toe and difficulty in walking on heels.
In babies there is a developmental delay, lax joints etc. In children over 8 there may be muscle contractions, muscle pain etc. (1)
Causes of hypotonia
Hypotonia in an infant may be due to multiple causes. Benign congenital hypotonia usually manifests at birth and shows up as normal limb movements and tendon reflexes along with weakness.
There may be mild or normal retardation in motor developments that improves with age.
In tests the levels of muscle enzymes and results from electromyography (EMG) and nerve conduction studies as well as muscle biopsy studies show up normal.
Who is affected by hypotonia?
The children affected have a 30% chance of having someone in the family with a similar affliction. Both boys and girls are equally affected. (1)
Four different sites of hypotonia
The cause of the condition lies at four different sites (1) –
- In the central nervous system (66 to 88% cases)
- In the peripheral motor and sensory nerves
- At the neuromuscular junction (the connection point where the nerve end meets the muscle to transmit the impulse for the muscle movement and contraction)
- At the muscle itself.
Two types of hypotonia
Hypotonia is basically a symptom of another underlying condition. It is of two types Congenital and acquired. (3)
Hypotonia is present at birth. This is usually an inherited or genetic condition that affects nerves, brain or muscles.
Some conditions that cause congenital hypotonia are Down’s syndrome, Marfan syndrome, dyspraxia, cerebral palsy etc.
The symptoms of hypotonia develop after birth as the result of an underlying medical condition, injury or trauma.
Conditions that may lead to hypotonia include muscular dystrophy (gradual weakening and damage of the muscles), brain infections like meningitis or encephalitis, head injury and myasthenia gravis (an auto immune disease where the immune system attacks healthy muscles leading to severe weakness.)
Diagnosis of hypotonia
Hypotonia is usually diagnosed at birth by the attending paediatrician. It may be followed up by a neurologist.
Treatment of hypotonia
Treatment plan involves managing the underlying cause.
Premature babies who are born with hypotonia may sometimes grow out of it by themselves.
Those with infections may be treated accordingly.
However, if the underlying cause cannot be treated, physiotherapy, occupational therapy and speech and language therapy may be alternative options. (2)
Edited by April Cashin-Garbutt, BA Hons (Cantab)