Vitamin B1 (thiamine)
ETIOLOGY.
water soluble = thiamine pyrophosphate or cocarboxylase,
functions as a coenzyme in carbohydrate metabolism.
required for the synthesis of acetylcholine,
deficiency results in impaired nerve conduction.
coenzyme in transketolation and in decarboxylation of a-keto
acids.
Transketolase participates in the hexose monophosphate shunt
that generates nicotinamide adenine dinucleotide phosphate and pentose.
sources
Breast milk
cow's milk
vegetables
cereals
fruits,
eggs
meats
legumes
destroyed by heat
Because the covering of grains of cereals contains the
vitamin, polishing reduces its availability.
Thiamine absorption decreases with gastrointestinal or liver
disease.
Requirements increase with fever, surgery, or stress.
Thiamine dependence has been described in a child with
megaloblastic anemia
and in maple syrup urine disease.
Large doses of thiamine improve some of the physical
abnormalities associated with Leigh's encephalomyelopathy
PATHOLOGY.
Heart
peripheral nerves
subcutaneous tissue,
serous cavities.
The heart is dilated, and fatty degeneration of the
myocardium is common
Generalized edema or edema of the legs, serous effusions,
and venous engorgement
nerves undergo degeneration of myelin and axon cylinders,
with wallerian degeneration, beginning in the distal locations.
The nerves of the lower extremities are affected first.
Lesions in the brain include vascular dilatation and
hemorrhage.
CLINICAL MANIFESTATIONS.
Early = fatigue, apathy, irritability, depression,
drowsiness, poor mental concentration, anorexia, nausea, and abdominal
discomfort.
Signs of progression = peripheral neuritis with tingling,
burning, and paresthesias of the toes and feet; decreased tendon reflexes; loss
of vibration sense; tenderness and cramping of leg muscles; congestive heart
failure; and psychic disturbances.:
ptosis of the eyelids and atrophy of the optic nerve.
Hoarseness or aphonia due to paralysis of the laryngeal
nerve
Muscle atrophy and tenderness of nerve trunks are followed
by ataxia, loss of coordination, and loss of deep sensation.
Paralytic symptoms are more common in adults than in
children.
signs of increased intracranial pressure, meningismus, and
coma .
In dry beriberi, …
appear plump but is pale, flabby, listless, and dyspneic
the heart rate is rapid,
the liver enlarged
In wet beriberi,
undernourished, pale, and edematous
dyspnea, vomiting, and tachycardia
The skin appears waxy.
urine may contain albumin and casts.
cardiac signs are cyanosis and dyspnea.
Tachycardia, enlargement of the liver
loss of consciousness,
convulsions
heart is enlarged, especially to the right.
The electrocardiogram shows increased Q-T interval,
inversion of T waves,
and low voltage, changes that rapidly revert to normal with treatment.
Cardiac failure may lead to death in chronic or acute
beriberi.
Wernicke's Encephalopathy.
Irritability
somnolence,
ocular signs
mental confusion and ataxias
it occurs in malnourished infants and children
Encephalopathy and beriberi has occurred during total
parenteral nutrition,
Associated conditions include malignancy, infection,
malnutrition gastrointestinal disorders (especially with malabsorption),
DIAGNOSIS.
lowered red blood cell transketolase and high blood or
urinary glyoxylate
Measurement of excretion after an oral loading dose of
thiamine - help to identify the deficiency state.
Clinical response to administration of thiamine is the best
test for thiamine deficiency.
PREVENTION.
diet containing sufficient amounts of thiamine
Thiamine requirements increase with a high-carbohydrate
content of the diet.
TREATMENT.
mother and child should be treated with thiamine.
The daily dose for
adults is 50 mg and
children 10 mg or more.
Oral administration is effective
heart is not permanently damaged.
Because patients with beriberi often have other B complex
deficiencies, all other vitamins of the B complex should be administered,
