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Hypotonia

Updated : April 3, 2023





Background

Hypotonia is characterized by poor muscle tone, resulting in a floppy build. It is identified by a decreased resistance observed with passive joint movements. However, it should not be confused with muscle weakness, which refers to reducing the maximum power a muscle can produce. Hypotonia can be challenging to diagnose as it is caused by various factors.

Nevertheless, physicians can adopt a systematic approach to identifying the underlying cause by taking a detailed medical history and performing a thorough physical examination. Although hypotonia is a recognizable condition, its diagnosis may be complex and can be associated with or without muscle weakness.

Epidemiology

Hypotonia is characterized by decreased muscle tone or strength. Although it is not a disease in itself, it can be a sign of various underlying conditions. Due to this, determining the exact incidence of hypotonia is difficult. Congenital hypotonia is the most common type of hypotonia. Central pathology, which refers to problems in the central nervous system, accounts for most cases, ranging from 60% to 80%.

Peripheral causes of hypotonia are less common and include conditions such as congenital muscular dystrophy, congenital myopathies, and spinal muscle atrophy. Acquired hypotonia, on the other hand, can be caused by toxins or infections, such as infant botulism. Infant botulism is a rare but potentially severe condition that occurs when infants ingest Clostridium botulinum spores, producing toxins affecting their nervous system and muscles.

Although hypotonia is rare worldwide, it is more frequently diagnosed in the United States due to greater clinician awareness. In particular, Utah, Pennsylvania, and California have higher incidences of infant botulism, with approximately 50% of cases occurring in California.

Anatomy

Pathophysiology

Hypotonia can occur due to several underlying causes, including neurological disorders, genetic, metabolic disorders, and developmental delays. The pathophysiology of hypotonia is complex and involves several different mechanisms. In general, hypotonia can be caused by a decrease in the number or function of muscle fibers, or by a decrease in the nervous system activity that controls muscle function. One possible cause of hypotonia is the impairment of the motor neurons that control muscle contraction. Motor neurons are the nerve cells that carry signals from the brain and spinal cord to the muscles, telling them to contract.

If there is damage to these motor neurons, the signals may be weakened or disrupted, leading to a decrease in muscle tone. This can occur as a result of neurological disorders such as cerebral palsy, spinal muscular atrophy, or Guillain-Barré syndrome. Another possible cause of hypotonia is a problem with the muscle fibers themselves. Muscles are composed of many muscle fibers, and if there is a decrease in the number or function of these fibers, the muscle may become weaker and less able to resist passive movement.

This can occur due to genetic conditions such as muscular dystrophy or metabolic disorders such as mitochondrial myopathy. In addition to these primary causes, several secondary factors can contribute to hypotonia. For example, if there is a decrease in the amount of calcium or ATP available to the muscle fibers, they may be less able to contract effectively. This can occur as a result of metabolic disorders or other conditions that affect the way the body produces or uses energy.

Etiology

Hypotonia is often present at birth and can be diagnosed in early infancy. There are several reasons why an infant may experience hypotonia, which can include abnormalities in the muscles, neuromuscular junction, or the central and peripheral nervous system. Furthermore, it may also present in various genetic disorders, metabolic diseases, endocrine problems, and acute or chronic illnesses.

In approximately 50% of the cases, the underlying cause of hypotonia can be determined with a thorough medical history and physical examination. Central causes may include hypoxic encephalopathy, brain insults, genetic syndromes, congenital or acquired infections, and metabolic disorders. On the other hand, peripheral causes may include myasthenia gravis, spinal muscular atrophy, drug or toxin exposure, hereditary neuropathies, muscular dystrophies, and congenital myotonic dystrophies.

Genetics

Prognostic Factors

The prognosis for individuals with hypotonia varies depending on the cause of the condition. Complete recovery with few to no complications is possible in transient myasthenia and infantile botulism.

In contrast, hypotonia associated with infections like sepsis or congestive heart failure usually improves with appropriate treatment. However, conditions like spinal muscular atrophy and Pompe disease can be life-threatening in the early stages.

Clinical History

Clinical History

The evaluation of a child with hypotonia is a critical step in identifying the underlying cause and determining appropriate management. This assessment involves obtaining a detailed history, including family and prenatal history. Family members with known causes of hypotonia, such as genetic disorders, muscular diseases, and consanguineous marriage, should be given particular attention.

Information about maternal exposure to toxins or drugs, method of delivery, gestational age, any infections during pregnancy, and Apgar score at birth. The onset of hypotonia and the clinical course can also provide valuable insights into the underlying cause. Hypotonia at birth with a low Apgar score may show hypoxic-ischemic encephalopathy, while poor muscle tone developing 12 to 24 hours after birth may suggest a metabolic disorder.

A neurodevelopmental assessment should be performed in older children, with tools such as the Bayley Scale III being valuable for assessing motor, language, cognitive, and social-emotional development for ages 1-42 months. However, evaluating children with profound weakness can be challenging using any standardized scale.

Additionally, a thorough review of all organ systems must be included in the assessment, as hypotonia may involve multiple systems. Such a review may assist in the diagnosis of the underlying etiology, as symptoms in other systems may indicate specific conditions. For example, respiratory symptoms may suggest a neuromuscular disorder, while gastrointestinal symptoms may indicate an inborn error in metabolism.

Physical Examination

Physical Examination

When evaluating a patient with hypotonia, performing a thorough physical and neurological examination is crucial. The examination should focus on identifying any dysmorphic features or associated congenital malformations. Additionally, the shape and size of the head should be assessed, and muscular strength should be evaluated, especially in infants with hypotonia. It is also essential to determine whether the hypotonia has progressed or remained static since onset.

Several maneuvers can be used to assess an infant’s tone, such as vertical suspension, horizontal suspension, the pull-to-sit maneuver and the Scarf sign. The vertical suspension tests the appendicular tone, while the horizontal suspension evaluates the ability to hold the head above the horizontal for some time. The Scarf sign assesses the appendicular tone in the shoulders, and the pull-to-sit maneuver assesses the ability to sit upright.

When evaluating weakness in an infant, decreased spontaneous movements can be a sign of weakness. The sucking reflex, cry, facial expressions, spontaneous movements, antigravity movements, and respiratory effort should be evaluated. The course and area involved should also be noted. Central hypotonia is characterized by normal muscle strength, reduced level of consciousness, and exaggerated reflexes. Primitive reflexes and clonus may persist, and dysmorphic features and congenital abnormalities may be present, pointing towards a syndromic cause of hypotonia.

Peripheral hypotonia, on the other hand, is characterized by a varying degree of impairment in the ability to move the extremities against gravity. Patients with peripheral hypotonia are usually alert, have a normal sleep-wake pattern, and respond appropriately to their surroundings. However, they may have delayed gross and fine motor skills, feeding difficulties, reduced or absent reflexes, respiratory impairment, and impaired ocular and facial movements.

Age group

Associated comorbidity

Associated activity

Acuity of presentation

Differential Diagnoses

Differential Diagnoses

Ullrich congenital muscular dystrophy

Myotubular myopathy

Congenital muscular dystrophy type 1A

Nemaline myopathy

Congenital myasthenic syndromes

Laboratory Studies

Imaging Studies

Procedures

Histologic Findings

Staging

Treatment Paradigm

Infants with central hypotonia require supportive treatment, which should be prioritized over encountering the underlying cause. The treatment should be customized based on the infant’s symptoms and may vary depending on the underlying cause. To ensure better outcomes, rehabilitation, respiratory support, and proper nutrition are essential components of the treatment plan.

In cases of central hypotonia, other than hypoxic-ischemic encephalopathy, metabolic experts and geneticists should be consulted. Speech, occupational and physical therapy are also vital as they significantly maximize muscle function and prevent secondary anatomic abnormalities. These therapies have proven to be beneficial for infants with central hypotonia.

Proper nutrition is crucial for these patients, who may be underweight and have various micronutrient deficiencies. It is important to address their nutritional needs, especially during illnesses when their requirements may increase. In severe cases where chest muscles are weak, percutaneous or nasogastric gastrostomy tubes may be needed for nutrition.

by Stage

by Modality

Chemotherapy

Radiation Therapy

Surgical Interventions

Hormone Therapy

Immunotherapy

Hyperthermia

Photodynamic Therapy

Stem Cell Transplant

Targeted Therapy

Palliative Care

Medication

Media Gallary

References

Hypotonia

Updated : April 3, 2023




Hypotonia is characterized by poor muscle tone, resulting in a floppy build. It is identified by a decreased resistance observed with passive joint movements. However, it should not be confused with muscle weakness, which refers to reducing the maximum power a muscle can produce. Hypotonia can be challenging to diagnose as it is caused by various factors.

Nevertheless, physicians can adopt a systematic approach to identifying the underlying cause by taking a detailed medical history and performing a thorough physical examination. Although hypotonia is a recognizable condition, its diagnosis may be complex and can be associated with or without muscle weakness.

Hypotonia is characterized by decreased muscle tone or strength. Although it is not a disease in itself, it can be a sign of various underlying conditions. Due to this, determining the exact incidence of hypotonia is difficult. Congenital hypotonia is the most common type of hypotonia. Central pathology, which refers to problems in the central nervous system, accounts for most cases, ranging from 60% to 80%.

Peripheral causes of hypotonia are less common and include conditions such as congenital muscular dystrophy, congenital myopathies, and spinal muscle atrophy. Acquired hypotonia, on the other hand, can be caused by toxins or infections, such as infant botulism. Infant botulism is a rare but potentially severe condition that occurs when infants ingest Clostridium botulinum spores, producing toxins affecting their nervous system and muscles.

Although hypotonia is rare worldwide, it is more frequently diagnosed in the United States due to greater clinician awareness. In particular, Utah, Pennsylvania, and California have higher incidences of infant botulism, with approximately 50% of cases occurring in California.

Hypotonia can occur due to several underlying causes, including neurological disorders, genetic, metabolic disorders, and developmental delays. The pathophysiology of hypotonia is complex and involves several different mechanisms. In general, hypotonia can be caused by a decrease in the number or function of muscle fibers, or by a decrease in the nervous system activity that controls muscle function. One possible cause of hypotonia is the impairment of the motor neurons that control muscle contraction. Motor neurons are the nerve cells that carry signals from the brain and spinal cord to the muscles, telling them to contract.

If there is damage to these motor neurons, the signals may be weakened or disrupted, leading to a decrease in muscle tone. This can occur as a result of neurological disorders such as cerebral palsy, spinal muscular atrophy, or Guillain-Barré syndrome. Another possible cause of hypotonia is a problem with the muscle fibers themselves. Muscles are composed of many muscle fibers, and if there is a decrease in the number or function of these fibers, the muscle may become weaker and less able to resist passive movement.

This can occur due to genetic conditions such as muscular dystrophy or metabolic disorders such as mitochondrial myopathy. In addition to these primary causes, several secondary factors can contribute to hypotonia. For example, if there is a decrease in the amount of calcium or ATP available to the muscle fibers, they may be less able to contract effectively. This can occur as a result of metabolic disorders or other conditions that affect the way the body produces or uses energy.

Hypotonia is often present at birth and can be diagnosed in early infancy. There are several reasons why an infant may experience hypotonia, which can include abnormalities in the muscles, neuromuscular junction, or the central and peripheral nervous system. Furthermore, it may also present in various genetic disorders, metabolic diseases, endocrine problems, and acute or chronic illnesses.

In approximately 50% of the cases, the underlying cause of hypotonia can be determined with a thorough medical history and physical examination. Central causes may include hypoxic encephalopathy, brain insults, genetic syndromes, congenital or acquired infections, and metabolic disorders. On the other hand, peripheral causes may include myasthenia gravis, spinal muscular atrophy, drug or toxin exposure, hereditary neuropathies, muscular dystrophies, and congenital myotonic dystrophies.

The prognosis for individuals with hypotonia varies depending on the cause of the condition. Complete recovery with few to no complications is possible in transient myasthenia and infantile botulism.

In contrast, hypotonia associated with infections like sepsis or congestive heart failure usually improves with appropriate treatment. However, conditions like spinal muscular atrophy and Pompe disease can be life-threatening in the early stages.

Clinical History

The evaluation of a child with hypotonia is a critical step in identifying the underlying cause and determining appropriate management. This assessment involves obtaining a detailed history, including family and prenatal history. Family members with known causes of hypotonia, such as genetic disorders, muscular diseases, and consanguineous marriage, should be given particular attention.

Information about maternal exposure to toxins or drugs, method of delivery, gestational age, any infections during pregnancy, and Apgar score at birth. The onset of hypotonia and the clinical course can also provide valuable insights into the underlying cause. Hypotonia at birth with a low Apgar score may show hypoxic-ischemic encephalopathy, while poor muscle tone developing 12 to 24 hours after birth may suggest a metabolic disorder.

A neurodevelopmental assessment should be performed in older children, with tools such as the Bayley Scale III being valuable for assessing motor, language, cognitive, and social-emotional development for ages 1-42 months. However, evaluating children with profound weakness can be challenging using any standardized scale.

Additionally, a thorough review of all organ systems must be included in the assessment, as hypotonia may involve multiple systems. Such a review may assist in the diagnosis of the underlying etiology, as symptoms in other systems may indicate specific conditions. For example, respiratory symptoms may suggest a neuromuscular disorder, while gastrointestinal symptoms may indicate an inborn error in metabolism.

Physical Examination

When evaluating a patient with hypotonia, performing a thorough physical and neurological examination is crucial. The examination should focus on identifying any dysmorphic features or associated congenital malformations. Additionally, the shape and size of the head should be assessed, and muscular strength should be evaluated, especially in infants with hypotonia. It is also essential to determine whether the hypotonia has progressed or remained static since onset.

Several maneuvers can be used to assess an infant’s tone, such as vertical suspension, horizontal suspension, the pull-to-sit maneuver and the Scarf sign. The vertical suspension tests the appendicular tone, while the horizontal suspension evaluates the ability to hold the head above the horizontal for some time. The Scarf sign assesses the appendicular tone in the shoulders, and the pull-to-sit maneuver assesses the ability to sit upright.

When evaluating weakness in an infant, decreased spontaneous movements can be a sign of weakness. The sucking reflex, cry, facial expressions, spontaneous movements, antigravity movements, and respiratory effort should be evaluated. The course and area involved should also be noted. Central hypotonia is characterized by normal muscle strength, reduced level of consciousness, and exaggerated reflexes. Primitive reflexes and clonus may persist, and dysmorphic features and congenital abnormalities may be present, pointing towards a syndromic cause of hypotonia.

Peripheral hypotonia, on the other hand, is characterized by a varying degree of impairment in the ability to move the extremities against gravity. Patients with peripheral hypotonia are usually alert, have a normal sleep-wake pattern, and respond appropriately to their surroundings. However, they may have delayed gross and fine motor skills, feeding difficulties, reduced or absent reflexes, respiratory impairment, and impaired ocular and facial movements.

Differential Diagnoses

Ullrich congenital muscular dystrophy

Myotubular myopathy

Congenital muscular dystrophy type 1A

Nemaline myopathy

Congenital myasthenic syndromes

Infants with central hypotonia require supportive treatment, which should be prioritized over encountering the underlying cause. The treatment should be customized based on the infant’s symptoms and may vary depending on the underlying cause. To ensure better outcomes, rehabilitation, respiratory support, and proper nutrition are essential components of the treatment plan.

In cases of central hypotonia, other than hypoxic-ischemic encephalopathy, metabolic experts and geneticists should be consulted. Speech, occupational and physical therapy are also vital as they significantly maximize muscle function and prevent secondary anatomic abnormalities. These therapies have proven to be beneficial for infants with central hypotonia.

Proper nutrition is crucial for these patients, who may be underweight and have various micronutrient deficiencies. It is important to address their nutritional needs, especially during illnesses when their requirements may increase. In severe cases where chest muscles are weak, percutaneous or nasogastric gastrostomy tubes may be needed for nutrition.