Vitamin B6 in carpal tunnel syndrome.

Abstract

To the Editor: The study by Dr Franzblau et al1 presents a common interpretation of the relationship between vitamin B6 status and carpal tunnel syndrome (CTS). For the past 5 years, we have also been measuring vitamin B6 status (plasma pyridoxal 5'-phosphate; PLP) in industrial workers as part of a study of the causes of median-nerve slowing and CTS in industry. Five important considerations cast doubt on the conclusions of Franzblau et al.1 First, many workers are taking vitamin B6 supplements specifically because they have hand/wrist symptoms. Inclusion of these workers in any analysis would bias the result in favor of the null hypothesis of no significant association. There is no indication that vitamin users were excluded. The high means and standard deviations suggest that there were vitamin B6 users in the population. Second, the distribution of raw plasma PLP levels is markedly skewed, making the use of parametric statistics such as t tests or linear correlation coefficients inappropriate without prior transformation of the raw plasma PLP levels. This was not done, as indicated by the extremely high standard deviations reported relative to the means (see Tables 4 and 51). Third, the inclusion of the erythrocyte glutamic pyruvic transaminase (EGPT, or the erythrocyte alanine aminotransferase [EALT] index) data is appropriate.2 The blood samples were frozen and then analyzed, however. Freezing and thawing is known to decrease transaminase activity. The range of EGPT index values (some of which are below 1:0) suggests that this was a problem. Thus, interpretation of this data is difficult. Fourth, there was no regression analysis to determine whether the vitamin B6 status measures made an independent contribution to predicting any of the outcome variables. It is not unusual for an independent variable, such as plasma PLP, that is not linearly correlated with the dependent variable, such as CTS symptoms, to nevertheless be an independent predictor of that dependent variable because of interactions with other independent variables, such as age. Fifth, to understand the relationship between CTS and vitamin B6, one must understand the pharmacology of vitamin B6 and the psychophysiology of symptom perception. Perhaps the proper question in this case has more to do with the frequency and severity of specific hand/wrist symptoms, such as pain/discomfort or nocturnal awakening, than with median-nerve slowing.3-7 As will be reported in greater detail in an article to follow, some of our findings with 390 workers from six industries and 51 exercise study volunteers agree with those of Franzblau et al1 and some do not. We view vitamin B6 as an effective analgesic in selected cases of CTS. We feel that the conclusion "... empiric treatment for CTS with vitamin B6 supplementation is unwarranted" cannot be drawn from the medical literature and the data presented by Franzblau et al. Richard C. Keniston, MD Pathologist; Portland Hand Surgery and Rehabilitation Center; Portland, OR James E. Leklem, PhD Department of Nutrition and Food Management; Oregon State University; Corvallis, OR Peter A. Nathan, MD Hand Surgeon; Portland Hand Surgery and Rehabilitation Center; Portland, OR