Prediabetes/early diabetes-associated neuropathy predominantly involves sensory small fibres

The aim of this study was to investigate the characteristics of prediabetes (preDM) and early (<3 years) diabetes mellitus type 2 (eDM2)-associated neuropathy and the value of recently proposed diagnostic criteria for diabetic sensorimotor polyneuropathy (DSPN). A prospective case-control study in a group of 48 consecutive patients with eDM2, 16 preDM patients and 40 age- and sex-matched normoglycaemic controls was performed. Clinical and laboratory diagnostic tests were used to detect neuropathic abnormalities; these were further classified in terms of recent diagnostic criteria. Criteria for confirmed DSPN based on abnormal nerve conduction (NC) studies were met in 7 (14.6%) eDM2 patients compared to no control (p < 0.05), and the proportion significantly increased to 37.5% compared to 2.5% controls (p < 0.001), if intraepidermal nerve fibre density (IENFD) was used as an alternative criterion in addition to NC. The subclinical DSPN criteria based on NC abnormalities were met in 4.2% eDM2 patients, while the proportion of preDM and eDM2 cases with subclinical sensory small-fibre involvement documented by IENFD reached 12.5% and 22.9% compared with 2.5% controls (p = 0.005 for eDM2). The absolute IENFD values from distal leg were significantly lower in both eDM2 (p < 0.0001) and preDM patients (p = 0.005) compared to controls. Neuropathy associated with preDM/eDM2 predominantly involves sensory small fibres.