• Diabetic Neuropathies
• Diagnostic Techniques and Procedures
• Foot Ulcer
• Diabetes Complications

Diabetic peripheral neuropathy (DPN) is causal in the development of foot ulceration and amputation.1 Most guidelines recommend easy-to-use chairside tests such as the 10 g monofilament and neurological examination to assess light touch, proprioception and ankle reflexes for the diagnosis of DPN.2 The 10 g monofilament evaluates large nerve fibers and identifies those with advanced DPN at high risk of diabetic foot ulceration (DFU). However, early diabetic neuropathy is characterized by small fiber damage.3 4

In a multicenter study of 506 patients with diabetes referred to neurology clinics for the assessment of DPN in Norway, Dunker and colleagues show that the 10 g monofilament has a sensitivity and specificity of 0.60 and 0.82, respectively.5 Furthermore, the diagnostic utility of the 10 g monofilament was worse in females, those with neuropathic pain and surprisingly those with more advanced DPN. The authors conclude:‘We do not recommend the use of the 5.07/10 g monofilament in the evaluation of patients with diabetes referred to polyneuropathy assessment’.

Are these findings surprising? Not really! Consistent with the current study, a systematic review and meta-analysis on the diagnostic utility of the 10 g monofilament showed a poor sensitivity of 0.53 and specificity of 0.88, generating a high likelihood of a false negative test result in the diagnosis of DPN.6 It may be time to challenge this failed strategy, given that the rate of DFU and amputation as well as re-amputation is increasing,1 and the vast majority of patients with DPN remain undiagnosed.7 A systematic screening strategy is required for the diagnosis of early DPN and risk factor interventions targeting obesity, physical inactivity, hyperglycemia, hypertension and hyperlipidemia to limit progression to more advanced DPN and DFU.7 The UK National Health Services diabetic eye screening program is an excellent example of effective implementation of population-level retinal screening which led to a significant reduction in the incidence of premature blindness in patients with diabetes.8

A major issue is the lack of time in a busy physician’s outpatient clinic, especially when dealing with patients with multiple comorbidities, in whom DPN is not a priority for the physician.9 How and where does one deploy screening for early DPN? A ‘one-stop-shop’ model has been deployed for the simultaneous assessment of retinopathy, nephropathy and neuropathy in Sheffield.10 Indeed, they showed that DPN was identified with the Toronto Clinical Neuropathy Score in 30.9%, but was markedly underestimated with the 10 g monofilament (14.4%) but was diagnosed in 61.9% of patients when combining large fiber nerve conduction (DPN-check) and small fiber sudomotor (Sudoscan) assessment, alongside microalbuminuria and retinal screening. Any strategy to diagnose early DPN must evaluate small fibers with high sensitivity and specificity. In this context, corneal confocal microscopy (CCM) may be useful as it is a rapid ophthalmic test of small fiber pathology with comparable sensitivity and specificity with intraepidermal nerve fiber density for the diagnosis of DPN.11 It also identifies subclinical DPN12 and predicts the development of clinical DPN13 and DFU.14 A one-stop-shop model which uses artificial intelligence-driven analysis of digital retinal fundus and corneal confocal microscopy images may enable rapid diagnosis of early diabetic retinopathy and neuropathy, respectively. In a pilot study in Manchester, 427 of 450 (94.9%) consecutive subjects with type 1 or type 2 diabetes attending for annual eye screening in primary care optometry settings successfully underwent CCM for the early diagnosis of DPN.15 This model requires further evaluation, but until then the physician must perform a comprehensive neurological examination which includes assessment of pin prick and thermal perception to assess small fiber damage that detects early DPN, rather than rely solely on the 10 g monofilament test.