Table of Contents
- Definition of Neurologic Disorders in Children
- Epidemiology of Neurologic Disorders in Children
- Etiology of Neurologic Disorders in Children
- Risk Factors for Neurologic Disorders in Children
- Classification of Neurologic Disorders in Children
- Pathophysiology of Neurologic Disorders in Children
- Diagnosis of Neurologic Disorders in Children
- Therapy of Neurologic Disorders in Children
- Prognosis of Neurologic Disorders in Children
Definition of Neurologic Disorders in Children
- Mental retardation (intellectual disability): below average intellectual function (usually full scale IQ <70) and below average adaptive behaviour
- Autism: developmental disorder where patients do not develop a theory of mind. This manifests as abnormal language, poor social skills, behavioural abnormalities and repetitive and stereotyped behaviours.
- Developmental regression: loss of previously attained developmental milestones with almost always a bad prognosis
- Neurocutaneous disorders: broad term for neurologic disorders that are lifelong conditions. These include:
Tuberous sclerosis complex
- Neurofibromatosis type 1 and type 2
- Sturge-Weber syndrome
- Familial telangiectasia
- Von Hippel-Lindau disease
- Incontinentia pigmenti
Not all disorders are discussed in detail in this article.
- Hypotonia: reduction in postural tone (floppy infant). Not necessarily associated with significant weakness.
Epidemiology of Neurologic Disorders in Children
- Cerebral palsy: incidence of around 3 in 1000 live births
- Autism spectrum disorders: incidence and prevalence of autism has increased rapidly in recent years. Around 1 in 100 children are diagnosed with some autism spectrum disorder.
- Neurocutaneous disorders:
- Tuberous sclerosis – autosomal dominant disease with incidence of 1 in 10,000
- Neurofibromatosis type 1 – autosomal dominant disease with an incidence of 1 in 3,000
- Neurofibromatosis type 2 – autosomal dominant disease that is far less common than neurofibromatosis type 1
Etiology of Neurologic Disorders in Children
Brain tissue begins to differentiate from the ectoderm at around 3 weeks. During weeks 3 to 4, neurulation (the formation and closure of the neural tube) takes place. The anterior (rostral) neural tube closes around 24 days. Failure of this process leads to anencephaly or encephalocele. Infants with anencephaly have no forebrain and as such have an open calvarium.
The posterior or caudal neural tube closes around 27 days. Failure can lead to myelomeningocele, meningocele and spina bifida. In a spina bifida there is a failure of the bony spinal canal to close. It can often be seen as a “tuft” of hair on the low back in patient with a minor deficit.
- A meningocele is when the meninges outpouch, or herniate, through the bony defect.
- A meningomyelocele is described when both the meninges and nervous system tissue bulge through the defect.
Around weeks 5-6 the vesicle forms. The prosencephalon forms the telencephaon and diencephalon. The mesencephalon remains undivided. The rhombencephalon forms the metencephalon and the myelencephalon.
- Holoprosencephaly can occur due to failure of prosencephalon cleavage. Holoprosencephaly is associated with mutations in the “sonic the hedgehog” gene. In severe instances patients will have cyclopia.
Between weeks 8 and 32, cellular proliferation and migration take place. The sulci and gyri form.
- Lissencephaly is a smooth cortical surface due to poor migration.
- Pachygyria is defined as large gyri.
- Microgyria is defined as small gyri.
- Schizencephaly is defined as a crack brain where a cleft exists due to defective morphogenesis (stroke can often be the cause).
Etiology of intellectual disability (mental retardation)
This can be caused by a number of factors including prenatal or postnatal trauma, hypoxic ischemic encephalopathy, perinatal infections (TORCH, HIV), chromosomal abnormalities as in Down’s or Fragile X, metabolic disorders as in hypothyroidism or Tay-Sachs disease. Toxins (e.g. alcohol in fetal alcohol syndrome) and perinatal hypoxic ischemic insult.
Developmental regression (the loss of previously attained developmental milestones) usually has an onset before age 2. It is caused by a number of disorders including:
- Mitochondrial disorders (MELAS – mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes)
- Neurocutaneous disorders: neurofibromatosis
- Gray matter disorders
- White matter disorders: metachromatic leukodystrophy
- Amino acid metabolism disorders: phenylketonuria
- Enzymatic disorders
Neurocutaneous disorders are genetic disorders. Tuberous sclerosis is caused by an autosomal dominant mutation in 2 genetic loci. Either TSC1 on chromosome 9 which codes for the protein hamartin or TSC2 on chromosome 16 which codes for tuberin.
Neurofibromatosis type 1 is an autosomal dominant disease caused by a mutation on chromosome 17 in the gene that codes for the protein neurofibromin.
Neurofibromatosis type 2 is an autosomal dominant disease that is caused by a mutation on chromosome 22 that codes for the protein Merlin.
Sturge-Weber syndrome is a somatic non-inherited mutation developmental abnormality in the neural crest. This is caused by activation of a gene called GNAQ. This affects small blood vessels and patients typically present with a classic “port wine” stain on the face.
A number of underlying conditions can cause hypotonia (floppy baby syndrome). These can be either congenital or acquired.
There are a number of causes of cerebral palsy and as such the disorder has multiple etiologies. Antenatal factors like premature birth and thyroid disease can lead to cerebral palsy. Perinatal factors like asphyxia have also been linked to the development of the condition.
Risk Factors for Neurologic Disorders in Children
Risk factors are events associated with the development of a disease. The underlying etiology behind how the risk events cause the disorder are not always known. Below are a number of risk factors for common pediatric neurological conditions.
In cerebral palsy, risk factors include:
- Low birth weight
- Prenatal viral infection
- Prenatal strokes
- Perinatal hypoxic-ischemic insult
Risk factors for autism spectrum disorders are:
- Male sex
- Positive family history
- Some genetic variant
- Chromosomal abnormalities
Classification of Neurologic Disorders in Children
A number of the disorders discussed in this article can be further classified into subtypes. These subtypes are discussed in more detail below.
- Classification of cerebral palsy: There are a number of classifications of cerebral palsy. The classification is based upon the type of motor abnormalities and their distribution in the patients. These include:
- Spastic (hypertonic) – most common
- Flaccid (hypotonic)
- Dystonic (athetoid)
- Classification of hypotonia (floppy baby syndrome): hypotonia can either be central or peripheral.
Pathophysiology of Neurologic Disorders in Children
Pathophysiology of cerebral palsy
Cerebral palsy has a number of underlying pathophysiological mechanisms dependent on the etiology of the condition. In the event of oxygen compromise during or just after birth there is a hypoxic ischaemic encephalopathy that may lead to insults to the periventricular white matter (particularly the internal capsule, leading to motor deficits).
As such, neural projections from the motor cortex are disrupted in the internal capsule and skeletal muscle response is as such affected. Fine motor control is often lost.
Pathophysiology of autism spectrum disorders
The complete pathophysiology of autism is not known. There are genetic factors, but their association is weak and a definition pathophysiology has not been deciphered. We do know that the disorder is neurodevelopmental and much research has been done on the altered function of hippocampal and amygdala brain structures (that are intimately tied to our emotions and empathy).
There are a few theories although these are not important to know. They include the theory of mind explanation of autism whereby autistic individuals are hypothesised to not have a “theory of mind” i.e. an understanding of the internal agency of others.
Diagnosis of Neurologic Disorders in Children
A clinical diagnosis of autism is not expected to be made in the USMLE step 1 but it is good to understand the general principles. Diagnosis of autism spectrum disorders is typically made clinically and by pediatricians. Most patients will have behavioural signs affecting their home and school life by 2 years. Babies are either quiet and placid or irritable and throw frequent tantrums.
Diagnosis is difficult because the severity of the disorder varies and many children display these types of symptoms without having an autism spectrum disorder. Many patients will fail theory of mind tests (e.g. the Sally Anne test).
Diagnosis of cerebral palsy is typically clinical. Examination will look at the range of motion, the power of movement and voluntary motor control. Thorough history should be taken and risk factors like teratogen exposure in pregnancy or asphyxiation during birth should be identified.
Patients with tuberous sclerosis typically present with the classic “Vogt’s” triad of symptoms. These are skin lesion, convulsive seizures and intellectual disability. Patients with tuberous sclerosis will have adenoma sebaceum, ungual fibroma, cortical tubers, subependymal nodules and multiple retinal astrocytomas. They then go on to develop infantile spasms, ash leaf spots (hypomelanotic macules), cardiac rhabdomyoma, renal angiolipomas.
Patients with neurofibromatosis type 1 will have Café au lait spots, axillary freckles and Lisch nodules (iris hamartomas). On investigation they have plexiform simple neurofibromas, optic gliomas, obstructive hydrocephalus and pheochromocytomas.
Patients with neurofibromatosis type 2 will on investigation have bilateral acoustic neuromas and can also develop multiple meningiomas.
Sturge-Weber syndrome can often be noticed by the “port wine” stain, or “nevus flammeus” stain that typically has a cranial nerve V distribution. Patients develop leptomeningeal angiomas and will suffer from seizures and intellectual disability. They may have early onset glaucoma.
Remember – hypotonia is not a diagnosis of a disease but a syndrome. When examining a patient with hypotonia it is important to identify underlying causes. Central hypotonia is typically associated with other signs of CNS dysfunction like seizures, developmental delay, microcephaly and dysmorphic features. Peripheral hypotonia has a lack of central sign; weakness is prominent.
Therapy of Neurologic Disorders in Children
Treatment of cerebral palsy is tailored for the individual patient. In children with cerebral palsy, current therapies include anticonvulsants, botulinum toxin, diazepam, fitness training and goal directed training amongst others.
There is no treatment for neurocutaneous disorders like neurofibromatosis and Von Hippel-Lindau syndrome. When tumours from, surgery is often the only option. Apart from surgery, most management will come from support and general counselling.
There is no cure for autism and therapy is based around improving social communication.
Prognosis of Neurologic Disorders in Children
The prognosis of cerebral palsy is highly dependent on the level of motor deficit and the intellectual ability of the sufferer. In most cases, cerebral palsy sufferers survive into adulthood and live to a senior age. Life expectancy has improved significantly in the last 10-20 years.
Autism spectrum disorders are lifelong and have a variable course often dependent on the severity of the disease in childhood. Many (around 15 %) will live independent lives. Another 15 to 10 % will need community living support. The most prognostic factors for independent living are cognitive and verbal capacity.
Those with neurofibromatosis type 1 rarely live beyond 50. Poor prognostic factors include childhood serious learning difficulties and optic gliomas amongst others.