Homocysteine and Vitamin B₁₂ Levels Related to MRI White Matter Abnormalities in Parkinson's Disease Dementia

son’s disease group. This finding could also be further analyzed by using the ROC curve which allows the determination of a cutoff point, and sensitivity and specificity values. Additionally, the percentage of patients with vitamin B 12 levels below the reference range was 5.3 and 14% in the Parkinson’s disease and PDD groups. The significantly lower vitamin B 12 levels in the PDD group should also be further evaluated by using urine or serum methylmalonic acid concentrations, which is accepted as a gold standard test for the assessment of functional or tissue levels of vitamin B 12 deficiency [3] . After all, this timely report draws our attention to the importance of these micronutrients for PDD patients. We read with great interest an investigation by Slawek et al. [1] on the total homocysteine (tHcy) levels and some vascular risk factors in relation to the white matter changes of Parkinson’s disease dementia (PDD). We congratulate the authors on their valuable article. It is not so easy to collect a great number of samples from PDD patients and make precise assessments. However, we would like to add a short note to help the readers to interpret the results of the study. In the study, the mean tHcy levels of patients and controls were found to be 17.75 8 7.86 and 13.6 8 7.39 mol/l, respectively. Although the authors accepted these values as being below the upper limit of their laboratory’s normative values (upper limit defined as 20.44  mol/l for females and 16.00 mol/l for males), the widely accepted upper limit for plasma tHcy levels is 12 mol/l, which is far below their values. Furthermore, the manufacturer of the tHcy determination kit they used also recommends the lower values. Thus, the increased tHcy levels in the patient and control groups should be clarified. One reason for elevated tHcy concentrations might be due to prolonged waiting times of samples at room temperature before centrifugation, which has been reported to cause abnormally increased tHcy measurements [2] . Although they did not find any relationship between tHcy and white matter abnormalities, higher tHcy levels were found in patients with PDD compared with the ParkinReceived: August 14, 2012 Accepted: September 27, 2012 Published online: December 12, 2012 D i s e a s e s