Small Fibers neuropathy Vitamin E role
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Vitamin E deficiency
Vitamin E is fat soluble and found in abundance in vegetable oils and wheat germ. It is carried in portal blood to the liver, and alpha- tocopherol transfer protein binds it and recycles vitamin E in the liver for incorporation into low density and very low density lipoproteins. The patients at risk for development of vitamin E deficiency include those with hypo or abetalipoproteinemia, other disorders of the pancreas and liver, such as cystic fibrosis, protein-calorie malnutrition, familial vitamin E deficiency, and other malabsorption states (Jackson et al 1996). Symptoms include areflexia, cerebellar ataxia, cutaneous sensory impairment, position and vibratory sense
abnormalities and less commonly, ophthalmoplegia, muscle weakness, nystagmus, extensor plantar responses, ptosis, and dysarthria. The peripheral neuropathy is usually limited to the legs and is mild, axonal, and sensorimotor in nature (Brin et al 1986).
13. Diagnostic Evaluation
Thiamin deficiency may be assessed by the transketolase assay. Because the carbohydratemetabolizing enzyme transketolase requires thiamin pyrophosphate, a deficiency will lead to anelevation in the red blood cell transketolase. The assay is most sensitive when performed with and without a thiamin pyrophosphate challenge. Serum thiamin levels are unreliable due to low sensitivity and specificity. MRI of the brain will occasionally show an abnormal signal in the periaqueductal gray matter and midline structures.
Cobalamin deficiency may be due to a variety of disorders, most commonly pernicious anemia. Approximately 78% of patients with cobalamin deficiency will be found to have a proven or probable defect of intrinsic factor production from the gastric parietal cell (pernicious anemia). Perhaps 10% of patients have food-cobalamin malabsorption due to hypo- or achlorhydria, a disorder that affects from 16-40% of the elderly ( Hurwitz et al, 1997). The rest are due to a variety of causes including malabsorption from inflammatory bowel disease, tape worm infestation, blind loop syndrome, chronic H2 blocker therapy, gastric bypass, and serum binding protein abnormalities. In a patient with signs and symptoms of cobalamin deficiency, one should begin with a cobalamin assay. If the serum cobalamin assay result is less than the lower normal limit, a measurement of intrinsic factor antibodies should be taken. If this test is positive, the diagnosis of pernicious anemia is confirmed, and a Schilling test is not necessary. In pernicious anemia, some laboratory evidence of an autoimmune process is often found. Anti- parietal cell antibodies are present in 90% and intrinsic factor antibodies in 60% of patients with pernicious anemia. Antiparietal cell antibodies have a 10% false positive rate. Though it lacks sensitivity, the test for intrinsic factor antibodies is much more specific.
In patients with serum cobalamin levels in the lower normal range, but in whom one still suspects clinical cobalamin deficiency, one should measure levels of homocysteine and methylmalonic acid (Snow, 1999; Kinsella and Green, 1995). Methylmalonic acid may be measured in serum or urine. The urinary assay is more specific in patients with renal insufficiency. If either metabolite is elevated, then serum intrinsic factor antibodies and gastrin should be measured. The serum gastrin level is often elevated in pernicious anemia and is a marker for achlorhydria, a cause of food- cobalamin malabsorption.
The presence of hypersegmentation may be a sensitive marker for cobalamin deficiency, even in the absence of anemia or macrocytosis. If metabolites or the serum gastrin are elevated, a Schilling test may be performed to identify cobalamin absorption, which is usually the result of autoimmune parietal cell dysfunction that occurs in pernicious anemia. Technically, patients with classic pernicious anemia have an abnormal test result when radioactive cobalamin alone is given by mouth (Part I). This abnormality is corrected when the test is repeated with intrinsic factor
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