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Hypotonia is a condition of abnormally low muscle tone (the amount of tension or resistance to movement in a muscle), often involving reduced muscle strength. Hypotonia is not a specific medical disorder, but a potential manifestation of many different diseases and disorders that affect motor nerve control by the brain or muscle strength. Recognizing hypotonia, even in early infancy, is usually relatively straightforward, but diagnosing the underlying cause can be difficult and often unsuccessful. The long-term effects of hypotonia on a child's development and later life depend primarily on the severity of the muscle weakness and the nature of the cause. Some disorders have a specific treatment but the principal treatment for most hypotonia of idiopathic or neurologic cause is physical therapy to help the person compensate for the neuromuscular disability.
- 1 Etiology of hypotonia
- 2 Signs and objective manifestations
- 3 Diagnosis
- 4 Prognosis and treatment
- 5 See also
- 6 References
- 7 External links
Etiology of hypotonia
Some conditions known to cause hypotonia include:
Congenital - i.e. present from birth (including genetic disorders presenting within 6 months)
- Genetic disorders are the most common cause
- Down's syndrome - most common
- Aicardi syndrome
- Canavan disease
- Centronuclear myopathy (including myotubular myopathy)
- Familial dysautonomia (Riley-Day syndrome)
- Infantile spinal muscular atrophy such as Werdnig-Hoffman disease
- Krabbe disease
- Marfan's syndrome
- Menkes syndrome
- Methylmalonic acidemia
- Nonketotic Hyperglycinemia (NKH) or Glycine Encephalopathy (GCE)
- Prader-Willi syndrome
- Tay-Sachs disease
- Trisomy 13
- 22q13 deletion syndrome
- Developmental disability
Acquired - i.e. onset occurs after birth
- Metabolic disorders
- Hypervitaminosis D
Signs and objective manifestations
Hypotonic patients may display a variety of objective manifestations that indicate decreased muscle tone. Motor skills delay is often observed, along with hypermobile or hyperflexible joints, drooling and speech difficulties, poor reflexes, decreased strength, decreased activity tolerance, rounded shoulder posture, with leaning onto supports, and poor attention and motivation. The extent and occurrence of specific objective manifestations depends upon the age of the patient, the severity of the hypotonia, the specific muscles affected, and sometimes the underlying cause. For instance, some hypotonics may experience constipation, while others have no bowel problems.
Since hypotonia is most often diagnosed during infancy, it is also known as "floppy infant syndrome" or "infantile hypotonia." Infants who suffer from hypotonia are often described as feeling and appearing as though they are "rag dolls" or a "sack of jello," easily slipping through one's hands. This image demonstrates the floppiness of a hypotonic infant. They are unable to maintain flexed ligaments, and are able to extend them beyond normal lengths. Often, the movement of the head is uncontrollable, not in the sense of spasmatic movement, but chronic ataxia. Hypotonic infants often have difficulty feeding, as their mouth muscles cannot maintain a proper suck-swallow pattern, or a good breastfeeding latch.
Children with normal muscle tone are expected to achieve certain physical abilities within an average timeframe after birth. Most low-tone infants have delayed developmental milestones, but the length of delay can vary widely. Motor skills are particularly susceptible to the low-tone disability. They can be divided into two areas, gross motor skills, and fine motor skills, both of which are affected. Hypotonic infants are late in lifting their heads while lying on their stomachs, rolling over, lifting themselves into a sitting position, remaining seated without falling over, balancing, crawling, and walking. Fine motor skills delays occur in grasping a toy or finger, transferring a small object from hand to hand, pointing out objects, following movement with the eyes, and self feeding.
Speech difficulties can result from hypotonia. Low-tone children learn to speak later than their peers, even if they appear to understand a large vocabulary, or can obey simple commands. Difficulties with muscles in the mouth and jaw can inhibit proper pronunciation, and discourage experimentation with word combination and sentence-forming. Since the hypotonic condition is actually an objective manifestations of some underlying disorder, it can be difficult to determine whether speech delays are a result of poor muscle tone, or some other neurological condition, such as mental retardation, that may be associated with the cause of hypotonia.
Muscle tone vs. muscle strength
The low muscle tone associated with hypotonia must not be confused with low muscle strength. In body building, good muscle tone is equated with good physical condition, with taut muscles, and a lean appearance, whereas an out-of-shape, overweight individual with fleshy muscles is said to have "poor tone." Neurologically, however, muscle tone cannot be changed under voluntary control, regardless of exercise and diet.
In an article by Diane E Gagnon, M.Ed., PT, she explains
- "True muscle tone is the inherent ability of the muscle to respond to a stretch. For example, if you quickly straighten the flexed elbow of an unsuspecting child with normal tone, the biceps will quickly contract in response (automatic protection against possible injury). When the perceived danger has passed, which the brain figures out really quickly once the stimulus is removed, the muscle then relaxes, and returns to its normal resting state.
- "...The child with low tone has muscles that are slow to initiate a muscle contraction, contract very slowly in response to a stimulus, and cannot maintain a contraction for as long as his 'normal' peers. Because these low-toned muscles do not fully contract before they again relax (muscle accommodates to the stimulus and so shuts down again), they remain loose and very stretchy, never realising their full potential of maintaining a muscle contraction over time. "
"A diagnosis of hypotonia is sometimes considered a form of muscular dystrophy or cerebral palsy, depending on the symptoms and the doctor. If the cause of the hypotonia is thought to lie in the brain, then it might be classified as a cerebral palsy. If the cause seems to be in the muscles, it might be classified as a muscular dystrophy, even though most forms of hypotonia are not seriously dystrophic. If the cause is thought to be in the nerves, it could be classified as either or neither. In any case, hypotonia is rarely an actual muscular dystrophy or cerebral palsy, and is often not classified as either one, or anything at all for that matter." 
Diagnosing a patient includes obtaining family medical history and a physical examination, and may include such additional tests as computerized tomography (CT) scans, magnetic resonance imaging (MRI) scans, electroencephalogram (EEG), blood tests, genetic testing (such as chromosome karyotyping and tests for specific gene abnormalities), spinal taps, electromyography muscle tests, or muscle and nerve biopsy.
Mild or benign hypotonia is often diagnosed by physical and occupational therapists through a series of exercises designed to assess developmental progress, or observation of physical interactions. Since a hypotonic child has difficulty deciphering his spatial location, he may have some recognizable coping mechanisms, such as locking the knees while attempting to walk. A common sign of low-tone infants is a tendency to observe the physical activity of those around them for a long time before attempting to imitate, due to frustration over early failures. Developmental delay can indicate hypotonia.
Other names for hypotonia
- Low Muscle Tone
- Benign Congenital Hypotonia
- Congenital Hypotonia
- Congenital Muscle Hypotonia
- Congenital Muscle Weakness
- Amyotonia Congenita
- Floppy Baby Syndrome
- Infantile Hypotonia
Prognosis and treatment
There is currently no known treatment or cure for most (or perhaps all) causes of hypotonia, and objective manifestations can be life long. The outcome in any particular case of hypotonia depends largely on the nature of the underlying disease. In some cases, muscle tone improves over time, or the patient may learn or devise coping mechanisms that enable him to overcome the most disabling aspects of the disorder. However, hypotonia caused by cerebellar dysfunction or motor neuron diseases can be progressive and life-threatening.
Along with normal pediatric care, specialists who may be involved in the care of a child with hypotonia include developmental pediatricians (specialize in child development), neurologists, neonatologists (specialize in the care of newborns), geneticists, occupational therapists, physical therapists, speech therapists, orthopedists, pathologists (conduct and interpret biochemical tests and tissue analysis), and specialized nursing care.
If the underlying cause is known, treatment is tailored to the specific disease, followed by symptomatic and supportive therapy for the hypotonia. In very severe cases, treatment may be primarily supportive, such as mechanical assistance with basic life functions like breathing and feeding, physical therapy to prevent muscle atrophy and maintain joint mobility, and measures to try and prevent opportunistic infections such as pneumonia. Treatments to improve neurological status might involve such things as medication for a seizure disorder, medicines or supplements to stabilize a metabolic disorder, or surgery to help relieve the pressure from hydrocephalus (increased fluid in the brain).
For most hypotonics, the National Institute of Health recommends "physical therapy [to] improve fine motor control and overall body strength. Occupational and speech-language therapy can help breathing, speech, and swallowing difficulties. Therapy for infants and young children may also include sensory stimulation programs." Ankle/foot orthoses are sometimes used for weak ankle muscles. Toddlers and children with speech difficulties may benefit greatly by using sign language.
Low-tone infants often have difficulty feeding, especially coordinating the suck-swallow reflex required for proper breastfeeding. Early diagnosis of hypotonic newborns can help mothers find the support and information they need to establish a successful breastfeeding relationship. Hypotonic babies may take longer to breastfeed because of the poor timing of sucking bursts and the need for long rests. If feeding is inefficient, they will also require greater feeding frequency. A baby with low muscle tone may suck better when the head and bottom are level, indicating pillow support in the lap. If the infant tends to arch his back, it may be helpful to swaddle the child loosely with arms drawn across the chest and legs drawn up toward the belly with a rounded spine during feedings. It may be necessary to support the infant's chin with one's hand if jaw, ear, and temple movement are not observed. If the baby tolerates touch to the mouth and face, the mother might gently rub the baby's lips and the outer surface of the gums to stimulate muscle sensitivity before beginning feeding. "If the tongue does not have the tone, strength, or range of motion to lift and press the breast against the palate (roof of the mouth), the baby might compensate by pressing more with his jaws. This excessive compression is painful for the mother. Getting a deeper latch, making sure the baby is not tongue-tied, and using an asymmetrical latch to increase the amount of tongue in contact with the breast can all be helpful to reduce compression."  Finally, if nursing is too frustrating and stressful for mother and child, breast milk can be expressed by use of a breast pump and fed through a bottle.
- Benign Congenital Hypotonia Site
- Exercises and Stimulation Therapy for Hypotonia from Early Parent Intervention Project (ARC Texas)
- Tone versus Strength by Diane E Gagnon, M.Ed., PT
- Breastfeeding an infant with neurological problems (PDF)
- Early recognition and intervention is the key to recovery for Benign Congenital Hypotonia Shannon Munro Cohen, RNC, BSN, and Teresa Whitt, Ph.D.
- Tactile Defensiveness and Other Sensory Modulation Difficulties (with Breastfeeding) Catherine Watson Genna, BS, IBCLC, New York City, New York, USA, From: LEAVEN, Vol. 37 No. 3, June-July 2001, pp. 51-53
- Characteristics of Hypotonia in Children: A Consensus Opinion of Pediatric Occupational and Physical Therapists. Pediatric Physical Therapy. 17(4):275-282, Winter 2005. Martin, Kathy PT, DHS; Inman, Jill PT; Kirschner, Abby PT; Deming, Katie PT; Gumbel, Rachel PT; Voelker, Lindsey PT
- National Organization of Rare Disorders
- National Institute of Neurological Disorders and Stroke
- National Rehabilitation Information Center (NRIC)
- Muscular Dystrophy Association (MDA)
- American Coalition of Citizens with Disabilities (ACCD)
- National Multiple Sclerosis Society (NMSS)
- March of Dimes Birth Defects Foundation
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