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General principles of nutritional disorders of the nervous system
- -diffuse
- -subacute
- -often symmetric
- -affect selectively vulnerable systems
- Most common phenotypes:
- -distal polyneuropathy
- -ataxia
- -non-specific cognitive dysfunction
- Causes:
- 1. not available in diet
- 2. inability to absorb or metabolize
- 3. poor diet due to chronic alcohol/vegan
- 4. toxic excess of nutrient
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Thiamine (B1) deficiency
- Causes:
- -Alcoholism
- -Malabsorption from chronic vomiting, primary GI disorders, short gut syndromes, bariatric surgery
- -Dietary restriction
- Two classic syndromes:
- -Wernicke Korsakoff
- -BeriBeri (dry and wet)
- -human body has 7-8 week store of thiamine
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Thiamine Deficiency: Wernicke Korsakoff
- -involves CNS
- -acute to subacute onset
- Presentation:
- 1. Ophthalmoplegia: weakness of EOM --> diplopia (esp LR), nystagmus
- 2. Ataxia (axial > appendicular)
- 3. Cognitive Syndrome: delirium, memory problems, basic amnesia syndrome, confabulation
- Pathology:
- -mammillary bodies (amnesia)
- -dorsomedial nucleus of thalamus (amnesia)
- -midbrain and pontine tegmentum (CNIII, CNVI nuclei --> ophthalmoplegia)
- -medulla (vestibular nuclei --> nystagmus, ataxia)
- -dilated capillaries with prominent endothelial cells --> hemorrhagic necrosis
- Pathophysiology:
- -unknown
- -genetic mutation in an enzyme that requires thiamine
- Treatment:
- -thiamine administration
- ***in patients with low thiamine levels glucose administration can trigger Wernicke Korsakoff syndrome
- Prognosis:
- -early treatment
- -ophthalmoplegia resolves (days)
- -ataxia improves partially (wks to months)
- -often congitive residua of basic amnesia syndrome
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Thiamine Deficiency: BeriBeri
- -involves PNS
- -two forms in adults: dry and wet
- -infantile variant in breastfed infants in areas with heavy white rice consumption
- Presentation:1. Dry BeriBeri
- -chronic progressive polyneuropathy
- -sensorimotor defect, may include pain
- 2.Wet BeriBeri
- -similar to dry
- -with associated heart failure
- 3. Infantile Variant
- -wet BeriBeri
- -eye movement abnormalities of Wernicke Korsakoff
- Pathology:
- -lesions most prominently in distal portions of longest and largest myelinated fibers
- -axonal degeneration
- Pathophysiology:
- -see Wernicke Korsakoff
- Treatment:
- -thiamine administration
- -drugs for neuropathic pain
- Prognosis:
- -tx prevents worsening
- -may or may not lead to gradual improvement (months)
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Cobalamin (B12) Deficiency
- -subacute onset (many weeks-months)
- -human body has 3 year store of cobalamin
- -may have megaloblastic anemia
- Presentation:
- 1. Subacute combined degeneration (dorsal columns and lateral corticospinal tracts) and large fiber polyneuropathy (predominantly sensory)
- -sensory paresthesias usually hands and feet
- -worsening distal somatosensory and motor dysfunction
- -impaired proprioception, vibration and fine touch
- -UMN findings in distal extremeties
- -sometimes ataxia
- 2. Neuropsychiatric effects (absent or mild)
- -trouble concentrating to overt dementia
- 3. Optic Neuropathy
- -decreased visual acuity (often later)
- Pathology:
- -demyelinating lesions starting in dorsal columns, lateral corticospinal tracts
- -low cervical to mid thoracic spinal cord
- -myelin sheaths swollen
- -intramyelinic vacuoles
- Pathophysiology:
- -often due to pernicious anemia
- -strict vegan diet, celiac sprue, GI resections, tapeworm etc
- Diagnosis:
- -normal range of cobalamin is very wide: can have normal levels and still be deficient
- -check homocysteine and methylmalonic acid levels
- Treatment:
- -IM cobalamin
- -large does oral supplements in pernicious anemia
- ***folate will correct the anemia but not neuro dysfxn of cobalamin deficiency
- Prognosis:
- -anemia resolves rapidly
- -neuro changes correct slowly over months and often incompletely
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Pyridoxine (B6) Deficiency
- Presentation:
- -polyneuropathy
- -seizures (rarely)
- Pathophysiology:
- -often in patients taking isoniazid for TB
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