Vitamin deficiencies

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Vitamin deficiencies


Vitamin deficiencies are a significant cause of neurologic disease in developing countries and in certain high-risk groups in developed countries (i.e. chronic alcoholics, patients with gastrointestinal diseases, and patients receiving long-term parenteral nutrition with inadequate vitamin supplementation). They can also result from lifestyle factors such as vegetarianism or from a wide variety of medical and psychiatric conditions. Evidence of the importance of vitamins for the wellbeing and normal function of the brain derives from data showing neurologic and psychologic dysfunction in vitamin deficiency states, and in inherited defects of vitamin metabolism. Vitamin deficiencies (particularly of B vitamins) are frequent in the elderly and may contribute to loss of cognitive function. Vitamin deficiencies have effects on the functional and structural integrity of the nervous system that are diverse and highly dependent on the degree of maturity of the system. For the pathologist there are significant difficulties in differentiating between changes that are specific and those that are secondary or non-specific. It is generally acknowledged that maternal nutritional status can affect the development of a number of organ systems in the infant including the brain.


Dietary deficiency of folate, vitamin B6 and B12 results in a significant increase of homocysteine levels, which has been shown to be a risk factor for developing Alzheimer’s disease (AD). Vitamin deficiencies can also affect the early development of the brain.



THIAMINE DEFICIENCY AND WERNICKE’S ENCEPHALOPATHY




MACROSCOPIC APPEARANCES


Lesions are usually discernible in the mamillary bodies (Fig. 21.1), but may also involve other parts of the hypothalamus, the medial thalamic nuclei, the floor of the third ventricle, the periaqueductal region (Fig. 21.1), the colliculi (Fig. 21.1), the nuclei in the pontomedullary tegmentum (Fig. 21.1) (particularly the dorsal motor nuclei of the vagus), the inferior olives, and the cerebral cortex. Typically, the involved regions are slightly shrunken and show brown discoloration due to hemosiderin deposition, and there may be petechial hemorrhages. The periventricular and periaqueductal lesions often spare a slender strip of subependymal tissue. In some patients, particularly those with previously treated disease, the mamillary bodies may be only mildly discolored and the brain may appear macroscopically normal.




image WERNICKE’S ENCEPHALOPATHY





MICROSCOPIC APPEARANCES


Acute lesions are edematous with relative preservation of neurons, variable necrosis of intervening tissue (Fig. 21.2), and loss of myelinated fibers. Capillaries may appear strikingly prominent due to endothelial hyperplasia and cuffing by macrophages (Fig. 21.2), but this is not a constant feature. There may be petechial hemorrhages and hemosiderin-laden macrophages (Fig. 21.3). Astrocytes show reactive changes.




Chronic lesions usually appear gliotic and slightly spongiotic, with mild loss of neurons, depletion of myelinated fibers, and scattered hemosiderin-laden macrophages and astrocytes (Figs 21.4, 21.5).




The histologic changes in Wernicke’s encephalopathy and Wernicke–Korsakoff syndrome are essentially identical. Studies suggest that Korsakoff’s psychosis occurs in those patients who have lesions involving the medial dorsal (or possibly other medial thalamic) nuclei (Fig. 21.6).




image WERNICKE’S ENCEPHALOPATHY




image This usually manifests acutely with gaze palsies and ataxia, which rapidly respond to thiamine administration.


image Apathy and clouding of consciousness (acute confusion/delirium) may form part of the initial presentation, though these symptoms often develop later if the encephalopathy is left untreated for more than a few days.


image Wernicke’s encephalopathy is sometimes associated with Korsakoff’s psychosis, which is characterized by retrograde and anterograde amnesia (i.e. impaired recall of events before the onset of illness and of new information), and confabulation. This does not respond to thiamine and is usually irreversible. The combination of Korsakoff’s psychosis with Wernicke’s encephalopathy is known as Wernicke–Korsakoff syndrome.


image Post-translationally modified variants of transketolase with a reduced affinity for thiamine pyrophosphate have been described in some chronic alcoholics with Wernicke–Korsakoff syndrome.



NICOTINIC ACID DEFICIENCY AND PELLAGRA




MACROSCOPIC AND MICROSCOPIC APPEARANCES


The brain and spinal cord appear macroscopically normal. Histologic changes in the CNS occur predominantly in the later stages of pellagra. Betz cells and neurons in the pontine and cerebellar dentate nuclei show striking chromatolysis without associated microglial or astrocytic changes (Fig. 21.7). Other neurons in the brain stem and the anterior horn cells of the spinal cord (Fig. 21.7) may also be affected. Symmetric degeneration of the dorsal columns, especially the gracile funiculi, and, to a lesser extent, of the corticospinal tracts, has been observed.




image NICOTINIC ACID DEFICIENCY AND PELLAGRA


Pellagra is caused by a deficiency of nicotinic acid or its amino acid precursor (i.e. tryptophan). Although fortification of bread and cereals with niacin has greatly reduced its prevalence, pellagra still occurs in developing countries where the primary source of calories is unfortified maize. Other causes include:




image PELLAGRA


The classic clinical triad of dermatitis, diarrhea, and dementia is often present only in part. The range of manifestations includes the following:


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Jul 20, 2016 | Posted by in NEUROLOGY | Comments Off on Vitamin deficiencies

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