Peripheral and central neurologic complications in type 2 diabetes mellitus: no association in individual patients.

Diabetes mellitus is associated with end-organ complications in the peripheral and central nervous system. It is unknown if these complications share a common aetiology, and if they co-occur in the same patient. The aim of the present study was to relate different measures of peripheral neuropathy in patients with type 2 diabetes mellitus (DM2) to cognition and brain MRI. A standardized neurological examination and questionnaire, neuropsychological examination and brain MRI were performed in 122 patients with DM2 and 56 matched controls. Measures of peripheral neuropathy were vibration threshold, a sensory examination sum score and the Toronto Clinical Neuropathy Scoring System. Neuropsychological test scores were expressed in standardized z-values across five predetermined cognitive domains. White matter lesions and cortical and subcortical atrophy were rated on MRI. Overall 38% of the patients with DM2 and 12% of the controls were classified as having any neuropathy (p<0.001). Patients with DM2 had a lower performance on the neuropsychological tests, more white matter lesions (p<0.01) and more atrophy (p<0.01) than controls. Within the DM2 group none of the measures of peripheral neuropathy was related to MRI abnormalities or cognitive dysfunction (linear regression analyses, adjusted for age, education, sex). We conclude that peripheral neuropathy in patients with DM2 is not related to cognitive dysfunction and brain abnormalities. This indicates that central and peripheral neurological complications of DM2 might have different etiologies.