Page 516 - Medicine and Surgery

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512 Chapter 13: Nutritional and metabolic disorders

legs with weakness, parasthesia and loss of ankle jerks. vere,chronic deficiency may lead to encephalopathy and
Cerebral involvement causes Wernicke–Korsakoff’s syn- spasticity.
drome (see page 317). Wet beriberi is the high output
heart failure caused by thiamine deficiency resulting in Management
oedema. Wet beriberi is rare in alcoholics. Supplementation with nicotinic acid and treatment of
other coexisting deficiencies.
Investigations
Diagnosisisusuallyclinicalandonresponsetothiamine.
Erythrocyte transketolase activity and blood pyruvate Vitamin B 6 (pyridoxine) deficiency
are increased. Definition
Deficiency of pyridoxine is rarely a primary disorder, but
Management it does occur as a secondary disorder.
Thiamine is replaced orally, intravenously or intramus-
cularly. The cardiac failure usually responds rapidly, but
Aetiology
neuropathies may only partially resolve if they are long-
Important sources of Vitamin B 6 are similar to those of
standing.
theotherBvitamins:liver,meat,wholegraincereals,veg-
etables and nuts. Deficiency may occur with malabsorp-
Niacin deficiency (pellagra) tion such as coeliac disease, dietary lack in alcoholism
and drug toxicity especially isoniazid.
Definition
Niacin (vitamin B 3 ) has two principle forms: nicotinic
Pathophysiology
acid and nicotinamide. Deficiency of niacin causes pel-
Pyridoxine is important in the metabolism of amino
lagra.
acids, especially tryptophan to nicotinic acid. In some
rare metabolic disorders, pyridoxine deficiency is as-
Aetiology
sociated with infantile convulsions and sideroblastic
Niacin is found in plants, meat and fish. It can also be
anaemia.
synthesised from tryptophan. Pellagra is seen in people
with a predominantly maize diet, low in tryptophan.
Clinical features
Othercausesincludeincreasedtryptophanconsumption
Marginal deficiency may cause stomatitis, glossitis, dry
in the carcinoid syndrome, prolonged use of isoniazid
lips, irritability and confusion. Deficiency causes men-
and Hartnup disease, an autosomal recessive congenital
tal confusion, glossitis, dry skin lesions and peripheral
disorder with reduced absorption of tryptophan from
neuropathy.
the gut and reduced amino acid re-uptake in the renal
tubules.
Management
Oral replacement; however, high doses may cause
Pathophysiology
Nicotinic acid is involved in energy utilisation. It is a neurotoxicity.
precursor of nicotinamide, as in NAD and NADP, which
are essential to glycolysis and oxidative phosphorylation. Vitamin B 12 deficiency
It is also used in maintaining skin, especially in sun-
exposed areas. Deficiency also causes villus atrophy in See page 471.
the small intestine.
Vitamin C deficiency
Clinical features
Pellagra is due to lack of nicotinic acid, it often occurs Definition
as part of a more general nutritional deficiency. Pellagra Vitamin C deficiency causes scurvy, which was first de-
presents with dermatitis, diarrhoea and dementia. Se- scribed by Lind in the eighteenth century.