Study designs of evaluations included in the review
Randomised controlled trials (RCTs) were eligible for inclusion. Uncontrolled trials and observational studies were excluded.
Specific interventions included in the review
Studies that assessed any type of vitamin B12 therapy, including coenzyme forms of vitamin B12 (methylcobalamin, cyanocobalamin, hydroxycobalamin), in either oral or injection form were eligible for inclusion. Studies involving combination therapy were also included if vitamin B12 or its coenzyme form was one of the treatment agents. The specific interventions assessed were vitamin B complex (B1, B6 and B12) as a combination agent, and methylcobalamin as a single agent. The duration of treatment ranged from 4 to 16 weeks.
Participants included in the review
Studies of participants with diabetic neuropathy were included. Diabetic neuropathy was defined as peripheral large- or small-fibre neuropathy resulting in autonomic or somatic sensory symptoms. Studies focusing on only a specific population, such as patients with uraemia, and studies in patients with other medical conditions were excluded. The primary studies were conducted in patients with type 1 and type 2 diabetes mellitus. In the included studies, the mean age of the patients was 50 to 60 years and the mean duration of diabetes mellitus, where reported, was 9 to 12 years.
Outcomes assessed in the review
Studies that reported clinical scores of somatic and autonomic symptoms or signs, vibrometer-detected thresholds of vibration perception, or electrophysiological measures such as nerve conduction velocities (NCVs) and somatosensory evoked potentials, were eligible for inclusion. The included studies used different methods to measure pain and somatosensory symptoms.
How were decisions on the relevance of primary studies made?
Two reviewers independently assessed studies for inclusion, with any disagreements being resolved by consensus.