Water-soluble vitamins are non-toxic and relatively cheap and can therefore always be given in excess if a deficiency is possible. The daily requirements of water-soluble vitamins.
Thiamine is a co-factor of many enzyme reactions, particularly in the glycolytic pathway. Body stores are small and signs of deficiency will quickly develop with an inadequate intake. Thiamine is found in many foodstuffs and deficiency is only seen:
• As beriberi, where the only food consumed is polished rice
• In chronic alcohol-dependent patients who are consuming virtually no food at all
• Rarely in starved patients, e.g. with carcinoma of the stomach; severe prolonged hyperemesis gravidarum, especially when treated by i.v. fluids alone
This is now confined to the poorest areas of South East Asia. It can be prevented by eating undermilled or parboiled rice, or by fortification of rice with thiamine. Probably the most important factor in the reduction of beriberi is the general increase in overall food consumption so that the staple diet is varied and contains legumes and pulses, which contain a large amount of thiamine. There are two main clinical types of beriberi, which, surprisingly, only rarely occur together.
DRY BERIBERI usually presents insidiously with a symmetrical polyneuropathy. The initial symptoms are heaviness and stiffness of the legs, followed by weakness, numbness, and pins and needles. The ankle jerk reflexes are lost and eventually all the signs of polyneuropathy that may involve the trunk and arms. Cerebral involvement occurs, producing the picture of the Wernicke-Korsakoff syndrome (p. 947). In endemic areas mild symptoms and signs may be present for years without unduly affecting the patient.
WET BERIBERI causes oedema. Initially this is of the legs, but it can extend to involve the whole body, with ascites and pleural effusions. The peripheral oedema may mask the accompanying features of dry beriberi. Thiamine deficiency results in inadequate metabolism of glucose and the accumulation of lactate and pyruvate, producing peripheral vasodilatation and eventually oedema. The heart muscle is also affected and heart failure occurs, causing a further increase in the oedema. Initially there are warm extremities, a full, fast, bounding pulse and a raised venous pressure (‘high output state’) but eventually heart failure advances and a poor cardiac output ensues. The electrocardiogram may show conduction defects.
INFANTILE BERIBERI occurs, usually acutely, in breastfed babies at approximately 3 months old. The mothers show no signs of thiamine deficiency but presumably their body stores must be virtually nil. The infant becomes anorexic, develops oedema and has some degree of aphonia. Tachycardia and tachypnoea develop and, unless treatment is instituted, death occurs quickly.
In endemic areas the diagnosis of beriberi should always be suspected and if in doubt treatment with thiamine should be instituted. A rapid disappearance of oedemaafter thiamine (50 mg i.m.) is diagnostic. Other causes of oedema must be considered, e.g. renal or liver disease, and the polyneuropathy is indistinguishable from that due to other causes. The diagnosis is confirmed by measurement of transketolase activity in red cells. This enzyme is dependent on thiamine pyrophosphate (TPP). The assay is performed with and without added TPP; an increase in activity of 30% with TPP indicates deficiency.
Thiamine 50 mg i.m. is given for 3 days, followed by 20 mg of thiamine daily by mouth. The response in wet beriberi occurs in hours, giving dramatic improvement, but n dry beriberi improvement is often slow to occur. In most cases all the B vitamins are given because of multiple deficiency. Infantile beriberi is treated by giving thiamine to the mother, which is then passed on to the infant via the breast milk.
Thiamine deficiency in patients with alcohol dependence
In the western hemisphere, this is the only major group to suffer from thiamine deficiency. Rarely they develop wet beriberi, which must be distinguished from alcoholic cardiomyopathy. More usually, however, thiamine deficiency presents with polyneuropathy or with the Wernicke- Korsakoff syndrome. This syndrome, which consists of dementia, ataxia, varying ophthalmoplegia and nystagmus (see p. 947), presents acutely and should be suspected in all heavy drinkers. If treated promptly, it is reversible, but if left, it becomes irreversible; it is a major cause of dementia in the USA. Urgent treatment with thiamine 50-100 mg i.m. or i.v. is given for 3 days, often combined with other vitamin B complex vitamins. Thiamine must always be given before any intravenous glucose infusion.