What is a Neurologic Disorder?
The term “neurologic disorder” applies to any condition that is caused by a dysfunction in part of the brain or nervous system, resulting in physical and/or psychological symptoms.
The development of the human brain begins during pregnancy and continues through infancy, childhood and adolescence. Most brain cells are formed before birth but the trillions of connections between these nerve cells (neurons) are not developed until infancy.
The brain is composed of gray matter (neurons and interconnections) and white matter (axons surrounded by a myelin sheath). A motor neuron (above) carries impulses away from the brain.
The brain is self-organizing. It selects information to forward its growth and development. It also adapts to the environment. Experience of the environment through the senses of touch, smell, sight, taste and hearing produces connections in the brain.
All neurologic disorders involve the brain, spinal column or nerves. Symptoms depend on where damage occurs. Areas that control movement, communication, vision, hearing or thinking can be affected.
Neurologic disorders are wide ranging. They have various causes, complications and outcomes. Many result in additional needs requiring life-long management.
Symptoms of neurologic disorders vary. Physical, cognitive (or thinking), emotional and behavioral symptoms may be present, with specific disorders having combinations or clusters of these symptoms. For example, cerebral palsy tends to have more physical symptoms whereas ADHD tends to have greater effects on behavior.
Many neurologic disorders emerge during the early years of development and may be diagnosed at birth. Some are diagnosed later because symptoms only appear when:
- A child misses developmental milestones or has developmental difficulties (e.g. autism).
- A damaging infection occurs (e.g. meningitis).
- An accident causes brain injury (stroke, trauma, hypoxia).
Causes of Neurologic Disorders
Many neurologic disorders are “congenital,” meaning they were present at birth. But some of the disorders are “acquired,” which signifies that they developed after birth. Those with an unknown cause are termed “idiopathic.”
Congenital Causes (present at birth)
Genetic factors can influence the development of a variety of neurologic disorders that are typically inherited from parents through genes and chromosomes.
Chromosomes are long strands of DNA supported by protein that are found in the nuclei of human cells.
Sections of DNA called genes carry the chemical code which makes us who we are. Chromosomes are composed of thousands of genes.
A human body cell normally contains 46 (23 pairs) of chromosomes, half inherited from the mother and half from the father.
- Gene abnormalities
Genes are responsible for determining characteristics. Changes in genes (called mutations) therefore change characteristics. Some mutations cause abnormalities that are damaging to individuals (for example, cystic fibrosis). Mutations can be passed on to offspring affecting their characteristics.
- Chromosome abnormalities
Changes in chromosomes, whether in number or in structure, have large effects on characteristics because they contain large numbers of genes.
- Change in chromosome number
The term monosomy refers to a loss of one chromosome out of a pair (for example, Turner syndrome). In trisomy, an extra chromosome has been gained by a pair (for example, Down syndrome).
- Change in chromosome structure
Microdeletions result in a loss of genes (fragments of DNA) from a chromosome. Microduplications occur when genes (fragments of DNA) are gained. Examples of such genetic conditions include cri-du-chat, Prader-Willi, and Angelman syndromes.
- Metabolic disorders
Metabolism refers to the chemical processes that occur in the body. Metabolic disorders can cause lasting damage and must be identified as early as possible (for example, through blood or urine tests). Examples of metabolic disorders include phenylketonuria (PKU) and homocystinuria. PKU is an inherited disorder where phenylalanine (present in food) can reach high concentration in blood serum. This causes damage to brain cells and to intellectual ability. Many metabolic disorders are detected at birth as blood samples are sent for ‘universal newborn screening’. In the United States, each state has its own guidelines as to what screening testing is done and not all countries have such screening programs
- Congenital malformation
Congenital ‘defects’ are believed to be the result of complex interactions between genes, environment and behaviors. An example is tuberous sclerosis, a condition where children have growths in regions such as the brain, heart, eyes, skin, kidneys and lungs. They may also experience epilepsy, learning difficulties/impairments and autism.
- Toxins and environmental factors
Neurotoxins can enter and damage a child’s developing system through the placenta during fetal development. Consequently a child may develop intellectual and behavioral problems. Neurotoxins include alcohol (linked to fetal alcohol syndrome), lead (linked to intelligence, learning and memory problems), mercury (linked to learning and development disorders), tobacco (linked to challenging behaviors and developmental impairments) and some food additives (linked to higher rates of ADHD in children).
- Nutritional deficiencies
Nutrients are needed for growth. 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)—for example, spina bifida (open spine).
TORCH infections, including sexually transmitted infections, can be passed from mother to baby during pregnancy. As reflected by the letters in the name, TORCH infections include Toxoplasmosis, Other infections (hepatitis B, syphilis, varicella-Zoster virus, HIV and Parovirus B19), Rubella, Cytomegalovirus and Herpes simplex virus. These infections can cause developmental abnormalities in the unborn child. Chorioamnionitis can be a cause of cerebral palsy.
Perinatal asphyxia is the condition resulting from a lack of oxygen (hypoxia). Hypoxic ischemia is insufficient blood flow causing reduced blood oxygen content. If a developing baby in the uterus does not have enough oxygen then it may have hypoxic ischemic encephalopathy (neurologic damage caused by low oxygen). The effects of severe HIE can include cerebral palsy, intellectual impairments and epilepsy.
- Complications during childbirth
The protective skull is not fully formed at birth making the brain vulnerable to physical injury. The supply of blood and oxygen from the umbilical cord can also become affected at birth. As the brain is dependent upon this supply of oxygen, deprivation of oxygen can cause brain damage.
- Prematurity/low birth weight
Low birth weight may indicate growth problems in the womb and has been associated with a greater likelihood of developing cognitive impairments, speech and language impairments, attention problems, social difficulties, hyperactivity and learning impairments. Some may arise because of associated complications during childbirth.
- Interaction effects
A number of factors, including heredity, gene expression, the environment, infectious disease, poor nutrition, stress, drugs and other chemicals, can interact in complex ways to cause some neurologic disorders.
Acquired Causes (developed after birth)
These are less common than congenital causes of neurologic disorders, and include:
- Immune disorders
Immune disorder, such as autoimmune encephalitis, can cause emotional challenges, abnormal body movements and seizures. Children with such problems can develop symptoms over several months and the diagnosis is challenging and frequently involves analysis of blood and cerebrospinal fluid.
- Postnatal infections
- Encephalitis (inflammation of the brain) can be caused by many types of infection (usually viral). Some children may develop neurologic long-term consequences following encephalitis, including memory problems, behavioral changes, speech impairments, and epilepsy.
- Meningitis is caused by a bacterial or viral infection that inflames the meninges (membranes surrounding the brain and spinal cord). The inflammation and swelling can damage the brain and nerves. Complications are more likely following bacterial meningitis than with viral meningitis. Lasting symptoms include hearing impairments, memory difficulties, coordination and balance problems, learning impairments, epilepsy, cerebral palsy, speech impairments, and loss of vision.
- Traumatic brain injury
This occurs when trauma to the head results in damage to the brain. There are three main types of traumatic brain injury (TBI):
- Closed head injuries – where no damage is visible; these are common in car accidents.
- Open wounds – where the brain is exposed and damaged by an object.
- Crushing injuries– where the head is crushed and brain damage occurs.
Evidence suggests that children’s brains are susceptible to lasting damage from TBI due to a disruption of the nervous system during development.
- Spinal cord injuries
Car accidents, falls, or sports accidents can cause spinal cord injuries. The degree of damage depends on where the damage occurs and what part of the body the injured spinal area controls. Spinal injuries can lead to loss of muscle function.
Neoplasm is an abnormal mass of tissue producing tumors. Tumors can develop in the brain or spinal cord. They can be benign (noncancerous) or malignant (cancerous). Malignant tumors are the most dangerous, so early diagnosis is very important. Benign tumors can have neurologic consequences as they increase pressure on other parts of the brain, damaging healthy tissue. Symptoms include seizures, limb weakness, difficulty walking, speech impairments and swallowing difficulties, strange sensations, learning impairments, challenging behaviors, or vision and hearing impairments.
Exposure to environmental chemicals or toxins during childhood can lead to neurologic impairment. Closed head injuries – where no damage is visible; these are common in car accidents.