WHAT IS A NEUROLOGIC DISORDER?
A neurologic disorder is caused by a dysfunction in the brain or nervous system (i.e. spinal cord and nerves). This dysfunction can result in physical and psychological symptoms.
The brain begins developing before birth. It continues developing throughout infancy, childhood, and adolescence. Most brain cells form before birth. One type of cell is the neuron, or nerve cell. Trillions of connections exist between neurons. These do not develop until infancy.
The brain is composed of:
- Gray matter. Neurons and the connections between them make up gray matter.
- White matter. Long fibers called axons make up white matter. An outer layer called the myelin sheath protects them.
A motor neuron carries impulses away from the brain.
The brain is self-organizing. It selects information to forward its growth. It also adapts to the environment. An individual experiences their environment through:
These senses produce connections in the brain.
Neurologic disorders involve the brain, spinal column, and nerves. Symptoms depend on where damage occurs. Affected areas may control:
Neurologic disorders are wide ranging. They have various causes, complications, and outcomes. Many require life-long management.
Symptoms vary as well. Types of symptoms include:
- Cognitive (or thinking)
Specific disorders have combinations or clusters of these symptoms. For example, cerebral palsy tends to have more physical symptoms. ADHD tends to affect behavior more.
Many neurologic disorders emerge during the early years of development. They may be diagnosed at birth. Some are diagnosed later. Symptoms may only appear when:
- A child misses developmental milestones or has developmental difficulties (such as with autism)
- A damaging infection occurs (such as with meningitis)
- An accident causes brain injury (such as with a stroke, trauma)
CAUSES OF NEUROLOGIC DISORDERS
Many neurologic disorders are congenital. This means they are present at birth. Some disorders are acquired. This means they develop after birth. Those with an unknown cause are called idiopathic.
Genetic factors can influence the development of some neurologic disorders. A child typically inherits them through genes and chromosomes, but these genetic changes are not always inherited from the parents – this is called de novo.
Chromosomes are long strands of DNA supported by protein. They exist in the center of cells. Genes are sections of DNA. They carry the chemical code that makes us who we are. Chromosomes are composed of thousands of genes.
A human cell normally contains 46 chromosomes (23 pairs). A child inherits half from their mother and half from their father.
Congenital causes of neurologic disorders include:
Genes determine a person’s characteristics. A mutation or variant is a change in a gene. Variants can change a person’s characteristics, though some variants are benign and will not cause disease. Some cause abnormalities that can be damaging (for example, cystic fibrosis). A parent can pass a mutation on to their children. This can affect the child’s characteristics.
Changes in chromosomes can greatly affect characteristics. They contain large numbers of genes. They can be abnormal in number or structure.
- Change in chromosome number
The term monosomy refers to a loss of one chromosome out of a pair (for example, Turner syndrome). In trisomy, a pair gains an extra chromosome (for example, Down syndrome).
- Change in chromosome structure
Microdeletions result in a loss of genes from a chromosome. Microduplications occur when a chromosome gains genes. Examples of such genetic conditions include:
- Cri-du-chat syndrome
- Prader-Willi syndrome
- Angelman syndrome
Metabolism refers to the chemical processes that occur in the body. Metabolic disorders can cause lasting damage. They must be identified as early as possible. Blood or urine tests can help diagnose them. Examples of metabolic disorders include:
- Phenylketonuria (PKU)
Phenylalanine is a building block for protein. It is present in many foods. PKU is an inherited disorder. It occurs when levels of phenylalanine in the blood become too high. This damages brain cells. It also affects intellectual ability.
Many metabolic disorders are detected at birth. Newborns have their blood screened. In the United States, each state decides which screenings are performed. Not all countries have such screening programs.
Congenital anomalies are believed to be the result of complex interactions between:
- The environment
An example is tuberous sclerosis. This is a condition where children have growths in regions such as:
- The brain
They may also experience:
- Learning difficulties and impairments
Prenatal and Perinatal Causes
A neurologic disorder can be caused during pregnancy (prenatal). It can also be caused throughout the period before, during, and after birth (perinatal). Such causes include:
Toxins and environmental factors
Neurotoxins can damage a child’s growing system. They enter through the placenta during fetal development. As a result, a child may develop intellectual and behavioral problems. Neurotoxins include:
- Alcohol (linked to fetal alcohol syndrome)
- Lead (linked to intelligence, learning, and memory difficulties)
- Mercury (linked to learning and development disorders)
- Tobacco (linked to challenging behaviors and developmental impairments)
- Food additives (linked to higher rates of ADHD in children)
Growth requires nutrients. A deficiency of nutrients during the last three months of pregnancy can decrease the number of brain cells. A deficiency of folic acid (a B vitamin) could lead to a neural tube defect (NTD). One example of an NTD is spina bifida (open spine).
A mother can pass a TORCH infection to her baby during pregnancy. These include sexually transmitted infections. As reflected by the letters in the name, TORCH infections include:
- Other infections (hepatitis B, syphilis, varicella-zoster virus, HIV, and parvovirus B19)
- Herpes simplex virus
These infections can cause developmental abnormalities in the fetus.
Perinatal asphyxia results from a lack of oxygen (hypoxia). With hypoxic ischemia, insufficient blood flow reduces oxygen in the blood.
A developing baby in the uterus may not have enough oxygen. When that occurs, it could have hypoxic ischemic encephalopathy (HIE). HIE results in neurologic damage caused by low oxygen. The effects of severe HIE can include:
- Cerebral palsy
- Intellectual impairments
Complications during childbirth
The protective skull is not fully formed at birth. This makes the brain vulnerable to injury. The supply of blood and oxygen from the umbilical cord can also become affected at birth. The brain depends on this supply of oxygen. So, deprivation of oxygen can cause brain damage.
Prematurity/low birth weight
Low birth weight may indicate growth problems in the womb. It has been associated with a greater likelihood of developing:
- Cognitive impairments
- Speech and language impairments
- Attention problems
- Social difficulties
- Learning impairments
Some may arise because of childbirth complications.
A number of factors can interact in complex ways to cause some neurologic disorders. Factors include:
- Gene expression
- The environment
- Infectious disease
- Poor nutrition
- Drugs and other chemicals
Acquired causes develop after birth. They are less common than congenital causes. They include:
Immune disorders, such as autoimmune encephalitis, can cause:
- Emotional challenges
- Abnormal body movements
Children with such problems can develop symptoms over several months. Diagnosis is challenging. It frequently involves the analysis of blood and cerebrospinal fluid.
- Encephalitis refers to inflammation of the brain. Many types of infection can cause it. It is usually viral. Children may develop neurologic long-term consequences following encephalitis. These include:
- Memory problems
- Behavioral changes
- Speech impairments
- The membranes surrounding the brain and spinal cord are called the meninges. Meningitis occurs when these become inflamed by a bacterial or viral infection. The inflammation and swelling can damage the brain and nerves. Complications are more likely following bacterial meningitis than with viral meningitis. Lasting symptoms can include:
- Hearing impairments
- Memory difficulties
- Coordination and balance problems
- Learning impairments
- Cerebral palsy
- Speech impairments
- Vision loss
Traumatic brain injury
A traumatic brain injury (TBI) occurs when head trauma damages the brain. There are three main types of TBI:
- Closed head injuries. No damage is visible. These are common in car accidents.
- Open wounds. An object exposes and damages the brain.
- Crushing injuries. The head is crushed and brain damage occurs.
Evidence suggests that children’s brains are susceptible to lasting damage from TBI. This is due to a disruption of the nervous system during development.
Spinal cord injuries
Car accidents, falls, or sports accidents are some causes of spinal cord injuries. The degree of damage depends on:
- Where the damage occurs
- What part of the body the injured spinal area controls
Spinal injuries can lead to loss of muscle function, loss of sensation, and loss of bowel/bladder control.
Neoplasm is an abnormal mass of tissue or tumor. Tumors can develop in the brain or spinal cord. They can be:
- Benign (noncancerous)
- Malignant (cancerous)
Malignant tumors are the most dangerous. So, early diagnosis is key. Benign tumors can have neurologic consequences. They increase pressure on other parts of the brain. This damages healthy tissue. Symptoms include:
- Limb weakness
- Difficulty walking
- Difficulty with speech and swallowing
- Strange sensations
- Learning impairments
- Challenging behaviors
- Vision and hearing impairments
Exposure to environmental chemicals or toxins during childhood can lead to neurologic impairment.