Dominic Stone
Hypotonia, or hypotonic muscles, is a medical term used to describe decreased muscle tone. It is often detected at birth or during infancy and is less common in adults. Hypotonia is not a specific medical disorder but a potential symptom of many different diseases and disorders that affect motor nerve control by the brain or muscle strength. It is characterised by low muscle tone and strength, resulting in poor movement and incomplete closure of certain valves. The condition can be central or peripheral, with central hypotonia associated with normal strength or mild to moderate weakness, and peripheral hypotonia associated with muscle weakness and the absence of antigravity movements.
| Characteristics | Values |
|---|---|
| Definition | Decreased resistance to passive muscle stretch or movement |
| Muscle Tone | Low |
| Muscle Strength | Reduced |
| Muscle Contraction | Decreased |
| Muscle Tension | Low |
| Muscle Feel | Soft and limp |
| Reflexes | Poor |
| Developmental Disorders | Determinant factor |
| Occurrence | More common in infants and children |
| Diagnosis | Challenging |
| Treatment | Occupational and physical therapy |
| Classification | Central, Peripheral, Cerebral Palsy, Muscular Dystrophy, Polyneuropathy |
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What You'll Learn
Hypotonia is a state of low muscle tone
Hypotonia is a medical term used to describe low muscle tone, which is the amount of tension or resistance to stretch in a muscle. It is often associated with reduced muscle strength, but the two should not be confused. Hypotonia is characterised by decreased resistance to passive muscle stretch or movement, which can contribute to hyperextension at the joints. It is not a specific medical disorder but a potential symptom of many different diseases and disorders that affect motor nerve control by the brain or muscle strength.
The condition is usually detected at birth or during infancy, and it is less common in adults. It is sometimes called "floppy baby syndrome" or "floppy infant syndrome", and it can cause abnormal limpness in the limbs, trunk, and head. In severe cases, hypotonic infants may have difficulty feeding due to an inability to maintain a proper suck-swallow pattern or a good breastfeeding latch.
The causes of hypotonia are generally different in children and adults. In adults, for example, hypotonia may be caused by Mikhail-Mikhail syndrome, which is characterised by muscular atrophy and cerebellar ataxia due to abnormalities in the ATXN1 gene. In children, the causes are often neuromuscular, encompassing primary muscular dystrophies, chromosome abnormalities, neuropathies, and inborn errors of metabolism. Determining the underlying cause of hypotonia can be challenging, and many cases cannot be definitively diagnosed. However, recognising the condition, even in early infancy, is usually relatively straightforward.
Hypotonia can be classified as central or peripheral. Central hypotonia is associated with normal strength or mild to moderate weakness, while peripheral hypotonia is associated with muscle weakness and the absence of antigravity movements. Central hypotonia originates from the central nervous system, while peripheral hypotonia is related to problems within the spinal cord, peripheral nerves, and/or skeletal muscles. Central hypotonia accounts for 60 to 80% of all hypotonia in infants.
Occupational and physical therapy can help people manage their low muscle tone, and early intervention can improve outcomes. Treatment generally focuses on providing support to the patient and their family to manage the condition.
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Hypotonia is not a specific medical disorder
Hypotonia is a state of low muscle tone, often involving reduced muscle strength. It 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.
Hypotonia is characterised by decreased resistance to passive muscle stretch or movement, which contributes to hyperextension at the joints. It is caused by problems with the nervous system, specifically the central nervous system (CNS) or the peripheral nervous system (PNS). The nervous system is important for maintaining normal muscle tone. The CNS consists of the brain and spinal cord, while the PNS consists of peripheral nerves and skeletal muscles.
The most common test for diagnosing hypotonia is observation, followed by the pull-to-sit test, and the adoption of a frog posture. Other diagnostic tests include blood tests, MRI and CT scans, spinal taps, electromyography muscle tests, and muscle and nerve biopsies.
The treatment for hypotonia depends on the underlying cause. If the cause is known, treatment is tailored to the specific disease, followed by symptomatic and supportive therapy. Physical therapy is often used to improve motor control and overall body strength in individuals with hypotonia.
In summary, hypotonia is a condition of low muscle tone that is not a specific medical disorder but a symptom of various underlying diseases and disorders. It is caused by problems with the nervous system and can be diagnosed through various tests. Treatment depends on the underlying cause and often includes physical therapy.
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Hypotonia can be classified as central or peripheral
Hypotonia is a condition of low muscle tone and strength. It is characterised by decreased resistance to passive movement of a muscle through its range of motion. It is a common problem in the neonatal and early infant period. Hypotonia can be classified as central or peripheral, depending on its origin.
Central Hypotonia
Central hypotonia is associated with normal strength or mild to moderate weakness. Antigravitational movements appear, although responses may be weaker. It is caused by a lesion in the efferent motor unit, specifically in CNS disorders above lower motor neurons, often with developmental delays and dysmorphic features. Central hypotonia may be generalized and affect the limbs, trunk and neck, or it may be localized with specific areas of the body being predominantly hypotonic, with others having normal or hypertonic characteristics. It is often seen in combination with muscle weakness and can interfere with functional activities such as reaching, sitting, standing and crawling/walking. Central hypotonia can also result in reflux and/or constipation due to abnormalities in the coordination of voluntary and involuntary muscle function.
Peripheral Hypotonia
Peripheral hypotonia is associated with muscle weakness and the absence of antigravity movements. It is determined by the peripheral nervous system, with the myotatic reflex being the main component of muscle tone. Peripheral hypotonia is caused by disorders of the peripheral nervous system. Purely peripheral neuromotor disorders will be discussed under Differential Diagnosis.
Diagnosis
The most used test in the diagnosis of hypotonia is observation, followed by the pull-to-sit test, and the adoption of frog posture. Electrophysiologic studies can be used as a screening tool for peripheral causes of hypotonia. If CK is mildly elevated (<10x normal) and electromyography (EMG) is myopathic, then a muscle biopsy will be needed. If the EMG is neuropathic, then testing for spinal muscular atrophy (SMA), hereditary sensorimotor neuropathy, and Dejerin-Sottas syndrome should be done.
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Hypotonia is a common problem in the neonatal and early infant period
The condition can be classified as central or peripheral hypotonia. Central hypotonia is associated with normal strength or mild to moderate weakness, and antigravitational movements may still be present, albeit with weaker responses. Peripheral hypotonia, on the other hand, is linked to muscle weakness and the absence of antigravity movements. In some cases, hypotonia may be the only symptom at birth or during early infancy, with cerebral dysgenesis being a suspected cause when associated with malformations in other organs or abnormalities in head size and shape. Brain injuries during the perinatal period or infancy, resulting from anoxia, hemorrhage, infection, or trauma, can also lead to hypotonia.
The identification of the underlying cause of hypotonia is crucial for determining prognosis, associated morbidities, and recurrence risk. Physical examination, patient history, basic laboratory testing, and imaging techniques such as magnetic resonance imaging (MRI) are all employed in the differential diagnosis of hypotonia. Electrophysiologic studies, muscle biopsies, and electromyography (EMG) can also aid in differentiating between various peripheral causes of hypotonia and guiding further treatment.
The prevailing therapeutic approach to hypotonia involves respiratory, physical, and occupational therapy, as well as attention to speech and feeding strategies. In cases of severe hypotonia, special feeding techniques may be required due to poor sucking and swallowing reflexes. While hypotonia is a common problem in the neonatal and early infant period, it often improves with time, and many infants with benign congenital hypotonia can achieve complete recovery.
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Hypotonia is associated with muscle weakness
Hypotonia, or low muscle tone, is defined by decreased resistance to passive movement, and may or may not be associated with decreased muscle strength or weakness. It is a common problem in the neonatal and early infant periods. The recognition of hypotonia in newborns may be straightforward, but determining its cause can be challenging. It is important for neonatologists, child neurologists, and other health providers to have an organised approach to its assessment.
Hypotonia can be classified as central and peripheral. Central hypotonia is associated with normal strength or mild to moderate weakness, and antigravitational movements appear, although responses may be weaker. Peripheral hypotonia is associated with muscle weakness and the absence of antigravity movements. It is a determinant factor in multiple developmental disorders and is associated with various characteristics and morbidities.
The most common test in the diagnosis of hypotonia is observation, followed by the pull-to-sit test, and the adoption of the frog posture. The pull-to-sit test involves pulling a supine infant to a sitting position. Head lag can be noticed in newborns, but it should disappear by 2 months of age. Hypotonic infants would have a significant head lag. When assessing weakness in an infant, the course and area of involvement must also be noted.
Hypotonia may be overt in its presentation, with the manifestations of low muscle tone apparent to family and the medical team alike. Other times, hypotonia may be insidious, subtly presenting to an examiner during a medical evaluation. It is rarely seen in isolation without some degree of weakness. Comparing the severity of weakness to the severity of hypotonia can be a helpful clinical tool in determining whether the origin is central or peripheral.
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Frequently asked questions
Hypotonia is the medical term for low muscle tone. It is characterised by decreased resistance to passive muscle stretch or movement, often resulting in hyperextension at the joints.
Symptoms of hypotonia include muscle weakness, hypermobility, poor reflexes, speech difficulties, and delays in reaching physical developmental milestones such as crawling, walking, and talking.
Hypotonia is typically diagnosed by a physician through a physical examination and patient history. Additional tests may include CT scans, MRI scans, blood tests, and muscle biopsies.
The causes of hypotonia vary and may be muscle, nerve, or central in origin. It is often a symptom of another condition, such as muscular dystrophy, polyneuropathy, or cerebral palsy. In adults, it may be associated with autism spectrum disorder (ASD).
