SLR - March 2011 - Andrew M. Hall
Reference: Chi-Chao Chao, MD; Ming-Tsung Tseng, MD, PHD; Ya-Jun Lin, MD; et al. Diabetes Care. Volume 33. Number 12. December 2010.
Scientific Literature Review
Reviewed by: Andrew M. Hall, DPM, PGY-2
Residency Program: Southern Arizona VA Healthcare System
Podiatric relevance:
Neuropathic pain is a common component of Type 2 diabetic neuropathy. Currently, there are two mainstream methods (both invasive) of diagnosing small-fiber sensory neuropathy: psychophysical assessments by measuring thermal thresholds on quantitative sensory testing and pathological evaluations by quantifying intra-epidermal nerve fiber density in skin punch biopsies. Recently, contact heat-evoked potential (CHEP) has been developed as a non-invasive, more clinically feasible method of evaluating the physiology of thermonociceptive nerve dysfunction.
The authors sought to investigate the following: 1) the changes in CHEP and its diagnostic role in diabetic neuropathy, 2) correlations of CHEP with the skin innervation and thermal thresholds, and 3) the relationship of CHEP and neuropathic pain in diabetic neuropathy.
Methods:
32 type 2 diabetic patients (20 males and 12 females, aged 51.63 +/- 10.93 years) were enrolled. The inclusion criteria were 1) symmetrical neuropathic pain in the feet and 2) pathological evidence of skin denervation. CHEPs were recorded with heat stimulations at the distal leg, where a skin biopsy was also performed.
Results:
CHEP amplitude was reduced in patients compared with age- and sex-matched control subjects (14.8 to15.6 vs. 33.7, p< 0.001). Abnormal CHEP patterns (reduced amplitude or prolonged latency) were noted in 81.3% of these patients. The CHEP amplitude was the most significant parameter correlated with IENF density (p=0.003) and pain perception to contact heat stimuli (p=0.019) on multiple linear regression models. An excitability index was derived by calculating the ratio of the CHEP amplitude over the IENF density. This excitability index was higher in diabetic patients than in control subjects (p=0.023), indicating enhanced brain activities in neuropathic pain. Among different neuropathic pain symptoms, the subgroup with evoked pain had higher CHEP amplitudes than the subgroup without evoked pain (p=0.011).
Conclusions:
The authors noted the following important findings:
1.) Abnormal CHEP patterns were found in most patients (81.3%) of diabetic peripheral neuropathy with skin denervation, and these findings could be neurophysiological characteristics in diagnosing small-fiber sensory neuropathy.
2.) The CHEP amplitude was the most significant parameter correlated with the IENF density and the pain perception to contact heat stimuli, and could represent the physiological consequences of thermonociceptive nerve degeneration.
3.) Patients with diabetic painful neuropathy had much higher CHEP amplitude relative to their corresponding IENF densities, especially the patients with evoked pain despite a similar degree of skin denervation.
In summary, contact heat-evoked potential offers a non-invasive, sensitive, and clinically practical method of evaluating the involvement and progression of peripheral neuropathy.