What is hypotonia?

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)

Congenital hypotonia

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.

Acquired hypotonia

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)

Causes of hypotonia

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.

  1. Central nervous system

    Central hypotonia with defects at the brain or spinal cord

  2. 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:

  • Cerebral palsy
  • Storage diseases – Inherited metabolic diseases that are caused due to lack of certain enzymes.
  • Congestive Heart failure
  • Hypoglycemia – Low blood sugar may lead to floppiness of the muscles
  • Myasthenia gravis – is an autoimmune disease that disrupts signals between nerves and muscles and affects the neuromuscular junction.

    There may be weakness and increased fatigue. Babies with mothers who have myasthenia gravis may be born with hypotonia.

  • Muscular dystrophy is a progressive muscle disease that leads to weakening of muscles and disability.
  • In adults muscle hypotonia may be seen in Multiple sclerosis where myelin is damaged or in Motor neurone disease that leads to progressive motor nerve damage.

Edited by April Cashin-Garbutt, BA Hons (Cantab)

Symptoms of hypotonia

Hypotonia is a condition where there is decreased resting muscle tone. It is a symptom of an underlying condition that may be congenital (present since birth) or acquired (manifested later in life).

General symptoms of congenital hypotonia

Congenital hypotonia usually manifests as (1-4):

  • Muscle weakness that is noticeable by the time the baby is six months old
  • Initial symptom is a weak cry and inability to suck or swallow
  • Little or no control of neck muscles leading to a floppy head and lack of head-holding
  • Feeling of a limp body when held
  • Inability to place any weight on legs or shoulders
  • The baby’s arms and legs hang straight down from sides, rather than bending at the elbows, hips and knees.
  • Delayed achievement of motor growth developmental milestones like sitting up, crawling, walking, talking or feeding themselves
  • Frequent falls and slipping off the high chair
  • If there are severe congenital myopathies there may be accompanying skeletal or bone and joint abnormalities. These include propensity for hip dislocation, deformities of the spine and foot.
  • On examination of a hypotonic child there is weakness of the muscles of the face, trunk or foot and ankle muscles.

    There may be ptosis or drooping eyelids, wing like outward protrusion of the scapula bones of the back and a thin body.

    There may be a protrusion of the abdomen due to weak abdominal muscles that are unable to hold in the contents of the abdomen.

  • Most patients with hypotonia may develop insufficiency of breathing and 50% of patients between ages 3 and 55 years need some form of artificial method to help them breathe at night.

Symptoms of congenital hypotonia that relate underlying conditions

  • Symptoms of mental retardation in cases of underlying conditions like Down’s syndrome
  • In Down’s syndrome, additional features include mental retardation, and congenital heart defects. There may be abnormal facial features like flat nose and nasal bridge, short neck, single transverse crease over the palm, upwardly slanting eyes etc.
  • In children with Fragile X syndrome there may be hypotonia along with features like mental retardation, large head (macrocephaly), large ears, and large testicles at puberty, autism like features etc.
  • Prader Willi syndrome is manifested as hypotonia, small genitals, short height and obesity.
  • Myasthenia gravis – If the baby develops transient or short term myasthenia due to an affected mother there may be symptoms like sepsis that include poor cry, poor suckling, hypotonia etc.

    In case of a baby affected primarily with myasthenia gravis the symptoms are exaggerated. There may be ptosis or drooping of the eyelids and respiratory or breathing difficulties.

Symptoms of acquired hypotonia

In case of acquired hypotonia or adults with hypotonia the usual manifestations include (3-4):

  • Clumsy behavior that progressively worsens
  • Frequent falls
  • Inability or difficulty getting up from a lying or sitting position
  • Difficulty in reaching for or lifting an object
  • High flexibility of joints called joint laxity. This may occur at hips, elbows and knees

Specific symptoms of hypotonia

Specific symptoms and signs of hypotonia include (2) –

  1. Central hypotonia – This is seen in 60-80% cases. There may be additional problems like seizures, inability to track a visual object, failure to imitate facial gestures, lethargy etc.
  2. Peripheral Hypotonia – Seen in 15-30% of cases. These patients manifest with feeding difficulties, generalized weakness and absence of muscle reflexes on testing.

Edited by April Cashin-Garbutt, BA Hons (Cantab)

Diagnosis of hypotonia

Hypotonia or lack of muscle tone is a sign of an underlying disease or condition. It may be seen at birth or may be acquired later in life. The aim of diagnosis is to detect the cause of the condition.

If hypotonia is detected in a newborn baby or child by a paediatrician, a referral to a neurologist of a specialist is made.

Who diagnoses hypotonia?

Management of hypotonia involves a multidisciplinary team. This includes an occupational therapist, physiotherapist, speech and language therapists an orthopaedic surgeon etc.

History of pregnancy

Diagnosis begins with detailed history: the mother is asked about her pregnancy and delivery.

She will be asked if any family member had a similar problem or if the baby suffered seizures after birth.

During pregnancy low fetal movements, breech presentation (this is the opposite of the normal head-down position of a baby inside the womb), increased or decreased amniotic fluid (polyhydramnios or oligohydramnios) etc. are relevant findings.

History of trauma at birth, premature delivery, late cry of the baby after birth, abnormal pH of the fetal umbilical cord blood etc. are also relevant findings.

Full physical examination

This is followed by a full physical examination. Some conditions can be detected with an initial physical examination.

For example, congenital genetic disorders like Down’s syndrome or congenital conditions like cerebral palsy may be detected with thorough clinical examination.

A frog like position, a “lag” or falling back of the head when the baby is pulled up to sitting position by the hands, weakness of the trunk and other muscles, laxity or over-flexibility of the joints are diagnostic clinical findings of hypotonia.

Tests for hypotonia

There are several tests and imaging studies advised for hypotonia, these include blood tests, assessment of cerebrospinal fluid and so forth. (1-4)

Blood tests

These can detect any routine abnormality. Blood biochemistry can show disturbance of any minerals or vitamins in blood.

Assessment of thyroid hormone in the blood can help detect hypothyroidism that may have caused the symptoms of hypotonia.

A complete blood count reveals if there is an infection in the body.

Sepsis (generalized infection) or infection of the brain or meninges (encephalitis or meningitis) may be suspected using routine blood tests.

Blood tests like metabolic panel tests are a series of blood tests may be prescribed to check whether the body’s metabolism is working properly. This can diagnose storage diseases.

Creatinine kinase levels may be disturbed in certain muscle disorders. Blood tests for creatinine kinase may be prescribed.

Assessment of Cerebrospinal fluid

Assessment of Cerebrospinal fluid (CSF) by lumbar puncture may be used to detect meningitis or encephalitis.

The CSF usually circulates throughout the brain and spinal cord. Any infection of the brain or its parts is detected using a microscopic examination of the CSF.

Muscle biopsy

A muscle biopsy may be prescribed in some patients. A small sample of muscle tissue is cut out from the muscle and sent to the pathologist who examines in under the microscope.

Sometimes electron microscopic picture of the muscle sample may be tested.

Other tests for hypotonia

Other tests for hypotonia include:

  • Computerized tomography or CT scan or Magnetic Resonance Imaging (MRI) scan to find out if there are any abnormalities or damage in the central nervous system
  • EEG (Electroencephalogram) – test to detect the electrical brain waves and brain activity
  • Electromyography (EMG) - Electrical activity of a muscle is recorded using needle like electrodes which are inserted into the muscle fibres
  • Nerve conduction velocity – The speech of conduction of an impulse via a nerve is measured using small metal disc electrodes placed over the skin over the nerve
  • Genetic testing may be recommended for parents and the affected child when an inherited disorder like Down’s syndrome etc. is suspected.
  • If no abnormalities are found the patient is termed to be suffering from benign congenital hypotonia.

Edited by April Cashin-Garbut, BA Hons (Cantab)