Diabetic neuropathy: a consideration of factors in onset

Peripheral neuropathy in type 2 diabetes mellitus in Isfahan, Iran: prevalence and risk factors

BACKGROUND

To estimate the prevalence and risk factors of peripheral neuropathy (PN) in people with type 2 diabetes mellitus.

METHODS

A total of 810 patients with type 2 diabetes (289 men and 521 women) from Isfahan Endocrinology and Metabolism Research Centre outpatient clinics, Iran, were examined. Part of examination included an assessment of neurological function including neuropathic symptoms and physical signs and nerve conduction velocity.

RESULTS

The prevalence of PN was 75.1% (95% confidence interval 72.1, 78.0). PN was associated with age, proteinuria, and duration of diabetes, insulin-treatment, and presence of any retinopathy and ischaemic heart disease (IHD). The age-adjusted prevalence rate of PN was 78% higher among patients with IHD, 64% higher among patients with any retinopathy, 66% higher among insulin-treated type 2 diabetes, and it was greater with duration of diabetes. Using a stepwise binary logistic regression model, age, duration of diabetes and proteinuria were significant independent predictors of PN.

CONCLUSION

Peripheral neuropathy is a common complication in this population of Iranian type 2 diabetic patients. It increases with age, duration of diabetes and proteinuria.

Experimental diabetes accelerates accumulation of fluorescent pigments in rat trigeminal neurons

The purpose of this study was to investigate autofluorescent pigment granules (lipofuscin, ceroid) in the trigeminal neurons (TN) during aging and streptozotocin-induced diabetes. Four young adult male rats were injected with streptozotocin (STZ; 50 mg/kg) to produce diabetes (DM), for comparison with four young uninjected control rats and four aged rats (90 weeks old). Eight weeks after STZ injection, all rats were fixed with 4% paraformaldehyde, and paraffin sections of TN were prepared and observed by fluorescence microscopy. We found the number of neurons with autofluorescent pigments had increased to 30.38% of the total in DM compared to 8.98% in the control group, and 25.36% in the aged rats. The area of autofluorescence within those neurons was 16.84% in aged rats, 13.02% in DM and 4.45% in the controls. Thus, DM caused accelerated accumulation of fluorescent granules in trigeminal neurons, and this change may show that premature aging contributes to neuronal functional decline and morphological change.

Elevated glycosylated hemoglobin in diabetic neuropathy

Glycosylated hemoglobin (GHb) levels were measured in 36 patients with established symptomatic neuropathy and in an identical number of matched controls. Strict criteria were employed in the selection of subjects and all had neuropathy of at least 12 months' duration. The diagnosis of neuropathy was supported by estimation of motor conduction velocities and vibration perception threshold. A semi-automated colorimetric technique, employing the reaction between thiobarbituric acid and 5-hydroxy-methyl furfural, was used for the estimation of GHb. Those patients with neuropathy had significantly higher GHb levels (58.2 +/- 11.3 mmol HMF/mol Hb) than the controls (50.0 +/- 8.9 mmol HMF/mol Hb) (p less than 0.01). This suggests that hyperglycemia or related metabolic abnormalities are important factors in established symptomatic neuropathy.

Glycosylated hemoglobin concentrations in patients with diabetic neuropathy

Glycosylated hemoglobin (Hb) concentrations were measured in 50 patients with clinically significant diabetic neuropathy. There were 24 males and 26 females with a mean age of 58.1 years and a mean duration of diabetes of 8.9 years. The glycosylated Hb concentration was not significantly different in these patients (13.9% +/- 2.4 SD) compared with randomly selected diabetic patients matched for age (+/- 5 years), sex and therapy without clinical evidence of neuropathy (13.6% +/- 2.2). There was no significant difference in the duration of diabetes between the two groups. The results would suggest that factors other than the degree of control of diabetes are important in the pathogenesis of diabetic neuropathy.

Serum pyridoxal concentrations in patients with diabetic neuropathy

Serum pyridoxal (vitamin B6) concentrations were measured in 50 patients with significant diabetic neuropathy. There were 24 males and 26 females with a mean age of 58.2 years and a mean duration of diabetes of 9.8 years. The level of pyridoxal was significantly lower in these patients when compared with randomly selected diabetic patients matched for age and sex without clinical evidence of neuropathy. There was no significant difference in the duration of the diabetes between the two groups. The results indicate an association between pyridoxal deficiency and neuropathy in diabetic patients.

Diabetic neuropathy: clinical aspects

The importance of diabetic neuropathy derives from its remarkable frequency and its clinical impact. In view of the varying underlying pathogenetic mechanisms and the resulting diversity of clinical representations, it becomes apparent that there are diabetic neuropathies, rather than a single entity of diabetic neuropathy. The scope of involvement is widespread with virtually every system at risk. Although peripheral neuropathy is by far the most common expression, visceral neuropathy is also highly significant. It may affect every part of the gastrointestinal tract, the genitourinary tract, and sexual function, as well as direct autonomic nerve pathology. Clearly, neuropathy in diabetes offers a specific and important diagnostic challenge to the clinician and plays a definitive role in differential diagnosis. The problem is heightened by the fact that any and all of the diabetic neuropathic syndromes may be the initial clinical manifestation of diabetes in the absence of covert manifestations of carbohydrate metabolic disorder. It is to be stressed that the diagnosis is more than an academic exercise, since each diabetic neuropathic syndrome carries with it some beneficial therapeutic modality to aid the patient.