出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/01/09 11:39:48」(JST)
| Hypotonia - Floppy Muscle Syndrome | |
|---|---|
| Classification and external resources | |
| ICD-10 | P94.2 |
| ICD-9 | 358,781.3 |
| DiseasesDB | 21417 |
| MedlinePlus | 003298 |
| MeSH | D009123 |
Hypotonia is a state of low muscle tone[1] (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 and/or occupational therapy for remediation.
Hypotonia is thought to be associated with the disruption of afferent input from stretch receptors and/or lack of the cerebellum’s facilitatory efferent influence on the fusimotor system, the system that innervates intrafusal muscle fibers thereby controlling muscle spindle sensitivity.[2] On examination a diminished resistance to passive movement will be noted and muscles may feel abnormally soft and limp on palpation.[2] Diminished deep tendon reflexes also may be noted.
Hypotonia is a condition that can be helped with early intervention.[citation needed]
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Some conditions known to cause hypotonia include:
Congenital - i.e. disease a person is born with (including genetic disorders presenting within 6 months)
Acquired - i.e. onset occurs after birth
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. 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 people with hypotonia may experience constipation, while others have no bowel problems.
The term "floppy infant syndrome" is used to describe abnormal limpness when an infant is prone.
Infants who suffer from hypotonia are often described as feeling and appearing as though they are "rag dolls," a "sack of jelly" or a "pillow full of pudding" 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 sometimes 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 manifestation 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. Additionally, lower muscle tone can be caused by Mikhail-Mikhail syndrome, which is characterized by muscular atrophy and cerebellar ataxia which is due to abnormalities in the ATXN1 gene.
The low muscle tone associated with hypotonia must not be confused with low muscle strength or the definition commonly used in body building. Neurologic muscle tone is a manifestation of periodic action potentials from motor neurons. As it is an intrinsic property of the nervous system, it cannot be changed through voluntary control, exercise, or diet.
"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."[5]
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.
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 them 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 to 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).
The National Institute of Neurological Disorders and Stroke states that physical therapy can improve motor control and overall body strength in individuals with hypotonia. This is crucial to maintaining both static and dynamic postural stability, which is important since postural instability is a common problem in people with hypotonia.[2] A physiotherapist can develop patient specific training programs to optimize postural control, in order to increase balance and safety.[2] To protect against postural asymmetries the use of supportive and protective devices may be necessary.[2] Physical therapists might use neuromuscular/sensory stimulation techniques such as quick stretch, resistance, joint approximation, and tapping to increase tone by facilitating or enhancing muscle contraction in patients with hypotonia.[2] For patients who demonstrate muscle weakness in addition to hypotonia strengthening exercises that do not overload the muscles are indicated.[2] Electrical Muscle Stimulation, also known as Neuromuscular Electrical Stimulation (NMES) can also be used to “activate hypotonic muscles, improve strength, and generate movement in paralyzed limbs while preventing disuse atrophy (p.498).”[2] When using NMES it is important to have the patient focus on attempting to contract the muscle(s) being stimulated. Without such concentration on movement attempts, carryover to volitional movement is not feasible.[2] NMES should ideally be combined with functional training activities to improve outcomes.
Occupational therapy can be used to assist with fine motor skill development and hand control, 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.
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| リンク元 | 「先天性筋無緊張症」 |
| 関連記事 | 「congenita」 |