Notes on Nervous System Disorders

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Cerebral edema:

Intracellular:

• Water moves into cells due to deficient Na/K pumps causing osmotic shift.

Extracellular:

• Increased vessel permeability due to: inflammation, metastasis, trauma, lead poisoning, respiratory acidosis, hypoxemia.

Findings:

• Intracranial hypertension, papilledema, headache, projectile vomiting without nausea, bradycardia.

Pseudotumor cerebri:

• Intracranial hypertension due to decreased CSF resorption.

• Increased CSF pressure and decreased CSF protein.

• Diagnosis: CT and MRI.

Cerebral herniation:

• Complication of increased intracranial pressure.

• Subfalcine herniation compresses the ACA.

• Uncal herniation compresses the mid-brain (Duret's hemorrhages), oculomotor nerve (dilated pupil and down-n-out eye), and PCA (occipital lobe hemorrhagic infarction).

Tonsillar herniation:

• Coning of cerebellar tonsils.

• Cardiorespiratory arrest.

Hydrocephalus:

• Ventricle enlargement due to increased CSF volume.

Communicating/non-obstructive:

• Increased CSF production.

• Obstruction of CSF absorption by arachnoid granulations.

Non-communicating (obstructive):

• CSF can't flow out due to stricture of aqueduct of Sylvius, fourth ventricle tumor, etc.

Findings:

• Seen in newborns (enlarged head) and adults (dementia, wide-based gait, urinary incontinence).

Hydrocephalus ex vacuo:

• Decreased brain mass causes dilated appearance of ventricles; eg., in Alzheimer's disease.

Developmental disorders:

• Neural tube defects: no fusion between lateral folds of neural plate or rupture of previously closed neural tube.

• Findings: increased maternal AFP in serum or amniotic fluid.

Arnold-Chiari malformation:

• Non-communicating hydrocephalus; platybasia.

Dandy-Walker malformation:

• Non-communicating hydrocephalus; cystic dilation of fourth ventricle.

Syringomyelia:

• Degenerative spinal cord disease; Arnold-Chiari association; disrupted lateral spinothalamic tracts; anterior horn cells destroyed.

Phakomatoses:

Neurocutaneous syndromes:

• CNS malformations or tumors.

Tuberous sclerosis:

• AD disorder.

• Mental retardation, seizures, ash leaf lesions, angiofibromas on face, hamartomatous lesions, rhabdomyoma in heart.

Neurofibromatosis:

• AD disease.

• Cafe-au-lait macules, pigmented neurofibromas.

• Lisch nodules, kyphoscoliosis, optic nerve glioma, meningioma, acoustic neuroma, pheochromocytoma, Wilms' tumor, neurofibrosarcoma.

Sturge-Weber syndrome:

• Vascular malformation on face and arteriovenous malformation in meninges.

Head trauma:

Cerebral contusion:

• Permanently damaged small blood vessels on brain surface.

• Acceleration-deceleration injury.

• Coup = site of impact; contrecoup = opposite side of impact.

Acute epidural hematoma:

• Blood-filled space between bone and dura due to arterial bleeding.

• Severed middle meningeal artery.

• Increased intracranial pressure.

Subdural hematoma:

• Venous bleeding between dura and arachanoid membranes.

• Blunt trauma.

• Fluctuating levels of consciousness.

CNS vascular disorders: global hypoxic injury:

Causes:

• Secondary to atherosclerosis of carotid artery.

• Chronic CO poisoning.

• Chronic hypoxemia.

Complications:

• Cerebral atrophy, watershed infarcts, cerebrovascular accident.

Cerebrovascular accidents:

Atherosclerotic (thrombotic) stroke:

• Most common.

• Platelet thrombus develops over disrupted plaque: MCA or ICA near bifurcation.

• Findings: pale infarction, swelling of brain, gliosis, cystic area.

• Clinical findings: strokes.

MCA stroke:

• Contralateral hemiparesis and sensory loss of upper extremity; expressive aphasia, visual defects, head and eyes deviate toward side of lesion.

• Vertebrobasilar arterial system stroke: vertigo, ataxia, ipsilateral facial sensory loss, comtralateral hemiparesis and sensory loss in trunk and limbs.

Embolic stroke:

• Emboli, usually originating from the left side of the heart, produce hemorrhagic infarction; most in distribution of the MCA.

Intracerebral hemorrhage:

• Due to hypertension-imposed stress on vessels.

• Charcot-Bouchard macroaneurysms.

• Common hemorrhagic sites: basal ganglia, thalamus, pons.

Subarachnoid hemorrhage:

Causes:

• Secondary to ruptured congenital berry aneurysm.

• Congenital berry aneurysm: develops at junctions of communicating branches with MCA due to hemodynamic stress or hypertension.

• Rupture releases blood into subarachnoid space; blood in CSF.

Findings:

• Sudden occipital headache.

Complications:

• Further hemorrhage, hydrocephalus, permanent neurologic deficits.

Lacunar infarcts:

• Caused by hyaline arteriosclerosis.

• Due to hypertension or diabetes mellitus.

CNS infections:

• Hematogenous spread; traumatic implantation.

Meningitis:

• Pia mater (brain cover) inflammation.

• Fever, nuchal rigidity, headache.

Labs:

• Viral: increased CSF protein; normal CSF glucose.

• Bacterial/fungal: increased CSF protein; decreased CSF glucose.

Encephalitis:

• Brain inflammation.

• Fever, headache, altered mental status.

Demyelinating disorders:

Multiple sclerosis:

• More common in females.

• HLA-DR2.

• CD8 T-cell destruction of myelin and oligodendrocytes.

Findings:

• Sensory and motor dysfunction, visual and speech disturbances, ataxia, tremor, nystagmus, bilateral internuclear ophthalmoplegia.

Labs:

• Increased CSF leukocyte, protein, myelin basic protein; normal CSF glucose; oligoclonal bands on CSF electrophoresis; central pontine myelinolysis.

Hereditary disorders:

Adrenoleukodystrophy:

• XR disease.

• Fatty acids cannot be oxidized; accumulate; demyelination in brain and adrenal insufficiency.

Metachromatic leukodystrophy:

• AR disease.

• Arylsulfatase A deficiency; defective lysosomal storage.

• Accumulation of sulfatides.

Krabbe's disease:

• AR disorder:

• Galactocerebroside beta-galactocerebrosidase deficiency; defective lysosomal storage.

• Accumulation of galactocerebroside.

• Brain has large, multinucleated, histiocytic cells (globoid cells).

Degenerative diseases:

Alzheimer's disease:

• Important role of beta-amyloid (A-beta) protein coded by chromosome 21.

• Defective degradation of APP.

• Apolipoprotein gene E on chromosome 19.

• Defective tau protein; located on chromosome 14.

Findings:

• Cerebral atrophy, dilated ventricles, NF tangles in neuron cytoplasm, senile plaques, amyloid angiopathy.

Confirmation:

• Postmortem examination of brain.

Parkinsonism:

• Altered dopaminergic pathways.

• Defective control over voluntary muscle movement.

Pathology:

• Idiopathic degeneration of neurons in substantia nigra causing deficiency of dopamine.

Findings:

• Muscle rigidity, resting/rolling pill tremor, expressionless face, shuffling gait.

Treatment:

• Dopamine replacement.

Huntington's disease:

• AD disease.

• Trinucleotide repeat disorder involving chromosome 4.

• Atrophy of striatal neurons.

Findings:

• Chorea, muscle rigidity, dementia.

Friedreich's ataxia:

• AR disease.

• Trinucleotide repeat disorder.

Findings:

• Ataxia, lack of joint sensation, peripheral neuropathy, hypertrophic cardiomyopathy.

Lou Gehrig's disease (ALS):

• Degeneration of UMNs and LMNs.

• Mutated chromosome 21.

• Findings: UMN: spasticity, Babinski's sign; LMN: muscle weakness causing respiratory paralysis.

Metabolic and toxic diseases:

Wilson's disease:

• AR disease.

• Defective synthesis of ceruloplasmin causing decreased copper excretion in bile.

• Findings: signs of Parkinsonism, chorea and dementia.

Acute intermittent porphyria (AIP):

• AD disorder.

• Deficiency of uroporphyrinogen synthase (porphobilinogen deaminase).

• Defective porphyrin disorder.

• Urine colorless when voided; turns black on light exposure due to oxidation of PBG to porphobilin.

• Findings: neurologic dysfunction, psychosis, peripheral neuropathy, dementia.

CNS and alcohol abuse:

• Cortical and cerebellar atrophy.

• Central pontine myelinolysis.

• Wernicke-Korsakoff syndrome due to thiamine deficiency.

• Findings: ataxia, confusion, nystagmus, ophthalmoplegia.

• Anterograde and retrograde amnesia.

CNS tumors:

Astrocytoma:

• 70% of all neurologic tumors.

• Involves frontal lobe (adults) and cerebellum (children).

• Eg., glioblastoma multiforme (GBM), a hemorrhagic tumor.

Meningioma:

• Most common adult benign brain tumor.

• Associated with neurofibromatosis.

• Psammoma/calcified (whorled pattern) bodies.

• Most common cause of focal seizures.

Ependymoma:

• Arises in cauda equine in adults and fourth ventricle in children.

Medulloblastoma:

• Malignant small cell tumor in children.

• Invades fourth ventricle.

Oligodendroglioma:

• Originates from oligodendrocytes in frontal lobe.

• Fried-egg appearance.

CNS lymphoma:

• Metastatic B-cell non-Hodgkin's lymphomas.

• Associated with AIDS, EBV.

Peripheral nervous system disorders:

Peripheral neuropathies:

• Demyelination and axonal degeneration.

• Glove-n-stocking sensory changes.

Charcot-Marie-Tooth (CMT) disease:

• AD disease.

• Inverted bottle appearance of legs.

Guillain-Barre syndrome (GBS):

• Autoimmune demyelination syndrome.

• Associated with M. pneumoniae pneumonia, C. jejuni enteritis, CMV, EBV, and HIV.

• Weakness of ascending motor neurons.

• Findings: increased CSF protein.

• Treatment: plasmapheresis.

Idiopathic Bell's palsy:

• Unilateral facial paralysis due to LMN palsy.

• Inflamed facial nerve.

• Associated with HIV, sarcoidosis, Lyme disease.

• Findings: drooping corner of mouth; can't speak; can't close eye.

• Causes: eg., vincristine, hydralazine.

• Deficiency of vitamins: thiamine, B12, pyridoxine.

Schwannoma (neurilemoma):

• Schwann cell-derived benign tumor.

• CN 5, 8 may be involved.

Acoustic neuroma (CN 8):

• Findings: association with neurofibromatosis.

• Tinnitus, deafness, CN 5 sensory changes.

Additional Reading:

Basic Pathology

1. Cell Injury
2. Inflammation and Repair
3. Immunopathology
4. Water, Electrolyte, Acid-Base, Hemodynamic Disorders
5. Genetic and Developmental Disorders
6. Environmental Pathology
7. Nutritional Disorders
8. Neoplasia
9. Vascular Disorders
10. Heart Disorders
11. Red Blood Cell Disorders
12. White Blood Cell Disorders
13. Lymphoid Tissue Disorders
14. Hemostasis Disorders
15. Blood Banking and Transfusion Disorders
16. Upper and Lower Respiratory Disorders
17. Gastrointestinal Disorders
18. Hepatobiliary and Pancreatic Disorders
19. Kidney Disorders
20. Lower Urinary Tract and Male Reproductive Disorders
21. Female Reproductive and Breast Disorders
22. Endocrine Disorders
23. Musculoskeletal Disorders
24. Skin Disorders
25. Nervous System Disorders
26. Notes on Tissue Regeneration
27. A Table of Bleeding Disorders
28. FAQ on Structure and Function of Red Blood Cells
29. FAQ on Components of Blood
30. Notes on Hemostatic Mechanisms
31. What is Fever?
32. What is Edema?
33. FAQ on Blood Pressure
34. FAQ on principles of fluid and flow dynamics of Blood
35. Causes of Thrombocytopenia
36. Squamous cell carcinoma of head and neck mucosa
37. Four tumors which never metastasize to the brain
38. What is caustic injury?
39. What causes Peripheral Edema?

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