Impaired glycemia and diabetic polyneuropathy: the OC IG Survey

Abstract

Objective: To test whether diabetic polyneuropathies (DPNs), retinopathy, or nephropathy is more prevalent in subjects with impaired glycemia (IG) (abnormality of impaired fasting glucose [IFG], impaired glucose tolerance [IGT], or impaired HbA(1c) [IA1C]) than in healthy subjects (non-IG).

Research design and methods: Matched IG and non-IG volunteers were randomly identified from population-based diagnostic and laboratory registries, restudied, and reclassified as non-IG (n = 150), IG (n = 174), or new diabetes (n = 218).

Results: Frequency (%) of DPN in non-IG, IG, and new diabetes was 3 (2.0%), 3 (1.7%), and 17 (7.8%) narrowly defined (no other cause for polyneuropathy) and 19 (12.7%), 22 (12.6%), and 38 (17.4%) broadly defined. Mean and frequency distribution of composite scores of nerve conduction and quantitative sensation tests were not significantly different between IG and non-IG but were worse in new diabetes. Frequency of retinopathy and nephropathy was significantly increased only in new diabetes. In secondary analysis, small but significant increases in retinopathy and nephropathy were found in IGT, IFG, and IGT combined groups.

Conclusions: In population studies of Olmsted County, Minnesota, inhabitants, prevalence of typical DPN, retinopathy, and nephropathy was significantly increased only in subjects with new diabetes-not in subjects with IG as defined by American Diabetes Association (ADA) criteria of abnormality of IFG, IGT, or IA1C. For atypical DPN, such an increase was not observed even in subjects with new diabetes. In medical practice, explanations other than IG should be sought for patients with atypical DPN (chronic idiopathic axonal polyneuropathy) who have IG.

Figure 1

Shown is the algorithm used to identify IG and non-IG patients from Mayo Clinic Rochester (MCR) and Olmsted Medical Center (OMC) disease and laboratory registries. At study (usually delayed by months), volunteers were classified by their IG status and microvessel complications (e.g., no DPN, DSPN, or atyp DPN) in non-IG, IG, and new diabetes (DM) groups. Eval., evaluation; Dx, diagnosis; Neuro, neuropathy; Tx, treated as DM.

Figure 2

Data are the prevalence and 95% CIs by IG classification and disease end point. P values are for unadjusted pairwise comparisons using Pearson χ² tests. ¹Typical DPN was significantly more frequent in new diabetes (DM) (6.0%) than in IG (0.6%, P <0.01) and more frequent than in non-IG (2.0%), although this latter difference was almost significant (P = 0.07). Atypical DPN was more frequent in DM (1.8%) than in non-IG (0.0%) or IG (1.%), but these differences were not significant. ²Typical DPN was more frequent in DM (8.3%) than in non-IG (5.3%) or IG (4.6%), but these differences were not significant. Atypical DPN was more frequent in DM (9.2%) than in non-IG (7.3%) or IG (8.1%), but these differences were not significant.

Figure 3

Cohorts studied are described in text (n = number of patients studied). Σ 2 NC nds is the sum of peroneal MNCV and sural SNAP nds; Σ 5 NC nds is the sum of peroneal CMAP, MNCV, and MNDL, tibial MNDL, and sural SNAP nds; Σ 4 NC nds is the sum of peroneal, tibial, and ulnar CMAP and sural SNAP nds; Σ 6 NC nds is the sum of peroneal, tibial, and ulnar MNCV and f-wave latency nds (all percentiles expressed in the lower tail of the distribution). Two-sample t tests: Σ 2 NC nds – 1 vs. 3 0.002, 1 vs. 5 <0.001, 2 vs. 3 <0.001, 2 vs. 5 <0.001, 3 vs. 4 <0.001, 3 vs. 5 <0.001, 4 vs. 5 <0.001; Σ 5 NC nds – 1 vs. 3 0.033, 1 vs. 5 <0.001, 2 vs. 3 0.044, 2 vs. 5 <0.001, 3 vs. 4 0.002, 3 vs. 5 <0.001, 4 vs. 5 <0.001; Σ 4 NC nds – 1 vs. 3 0.008, 1 vs. 5 <0.001, 2 vs. 3 <0.001, 2 vs. 5 <0.001, 3 vs. 4 0.002, 3 vs. 5 <0.001, 4 vs. 5 <0.001; Σ 6 NC nds – 1 vs. 3 0.006, 2 vs. 3 <0.001, 3 vs. 4 0.002. Among 1, 2, and 4, there were no significant differences for any composite score. CMAP, compound muscle action potential; MNCV, motor nerve conduction velocity; MNDL, motor nerve distal latency; SNAP, sensory nerve action potential.