The quality of evidence is downgraded by study limitations (unclear allocation concealment) and upgraded by large magnitude of effect.
A Cochrane review included 17 studies to investigate the effects of enhanced glycaemic control on neuropathy in patients with DM after at least one year of intervention. Primary outcome was defined as development of clinical neuropathy. Secondary outcomes included motor nerve conduction velocity and quantitative vibration testing. Definition of enhanced glucose control varied across studies; included were all measures aimed to improve control (multiple injections, insulin pump, education etc.). Results of the The studies concerning patients with type 1 DM are summarized here.
| Outcome | Number of participants (studies) | Assumed risk (control) | Corresponding risk (intervention) | Relative effect (95% CI) |
|---|---|---|---|---|
| Incidence of clinical neuropathy after 5 years | 1228 (3) | 173 per 1000 | 79 per 1000 (57 to 109) | RR 0.46 (0.33 to 0.63) |
| Annual change in vibration threshold in the feet | 177 (3) | -0.62 SMD (mean annual change) | 0.32 SD higher (0.02 to 0.62 higher) | RR 0.32 (0.02 to 0.62) |
| Annual change in peroneal nerve motor conduction | 1371 (4) | -0.25 m/sec (mean annual change) | 0.61 higher (0.51 to 0.71 higher) | RR 0.61 (0.51 to 0.71) |
Three studies measured clinical neuropathy, which was defined as the presence of 2 or more of the following: symptoms, sensory examination findings, and decreased or absent reflexes. The cohort was divided to primary prevention group (IDDM of 1 to 5 years' duration, no detectable retinopathy, and urinary albumin excretion less than 40 mg/24 hour) and secondary prevention group (IDDM of 1 to 15 years' duration, very mild to moderate non-proliferative retinopathy, and urinary albumin excretion less than 200 mg/24 hour).
At five years in the primary prevention cohort, there was a decrease in the incidence of clinical neuropathy in the participants randomized to intensive treatment (n=251) compared to standard treatment (n=292): annualized RD -1.53% (95% CI -2.54 to -0.51), RR 0.47 (95% CI 0.27 to 0.80).
In the secondary prevention cohort (n = 642, 327 intensive, 315 conventional), the annualized RD was -1.97% (95% CI -3.04 to -0.90) in favor of enhanced glucose control at five years (RR 0.48, 95% CI 0.32 to 0.73).
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