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,