An observational study of vitamin b12 levels and peripheral neuropathy profile in patients of diabetes mellitus on metformin therapy.

METHODS: A descriptive, observational study was completed in a tertiary care hospital between November 2014 and March 2016. Fifty consecutive patients of Type 2-Diabetes Mellitus who had been on metformin therapy for at least three months were included in our study. Several Parameters were compared with vitamin B12 levels and severity of peripheral neuropathy (using Toronto Clinical Scoring System (TCSS) and Nerve Conduction Velocity). These included the duration of diabetes, duration of metformin usage, dietary history, and HbA1c levels. Definite B12 deficiency was defined as B12<150pg/ml and possible B12 deficiency as <220pg/ml.

RESULTS: In our study, we found a negative correlation between duration of metformin use and Vitamin B12 levels(r=-0.40). The mean Vitamin B12 levels seen in our study was 212.3pg/mL. There is a positive correlation between the duration of metformin therapy and peripheral neuropathy (r=0.40). The mean TCSS score was 6.8. The percentage of patients with mild neuropathy was 28%, with moderate neuropathy was 20% and severe neuropathy in 12% of the patients. The average duration of metformin use in patients without peripheral neuropathy was 5.5yrs whereas the average length of metformin use in patients with peripheral neuropathy was 10.4 yrs.

CONCLUSION: Patients on long-term metformin therapy are at a high risk for Vitamin B12 deficiency and peripheral neuropathy. Interval Screening for peripheral neuropathy is recommended for patients on metformin even if Vitamin B12 levels appear to be normal.