Impaired glucose tolerance and metabolic syndrome in idiopathic polyneuropathy: The role of pain and depression

Chronic idiopathic axonal polyneuropathy (CIAP) is referred to as axonal neuropathy after an adequate workup fails to determine a cause. A subgroup of patients with CIAP has impaired glucose tolerance (IGT). These patients have been considered by some investigators to have a neuropathy as a result of IGT and/or metabolic syndrome (MetS). Patients with CIAP usually suffer from chronic pain and associated depression, both of which have been proposed to cause insulin resistance (IR) by such mechanisms as a sustained increase in the corticosteroids and catecholamines, and chronic low grade inflammation. In a pilot study of 14 patients with CIAP + IGT and eight normal controls, we found a correlation between the number of features of the MetS with scores of pain and depression. There was no increase in the frequency of retinopathy and nephropathy in these patients, contrary to what would have been expected if chronic hyperglycemia was the cause of the neuropathy. We hypothesize that neuropathy has an unclear cause in the majority of patients with CIAP + IGT/MetS – and IGT/MetS are a result of comorbidities of CIAP, including chronic pain and depression.