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Shyam Sunder Tummanapalli, Mark Willcox, Tushar Issar, Aimy Yan, Natalie Kwai, Ann Poynten, Arun Krishnan, Maria Markoulli; Reduced tear film substance P concentration is associated with diabetic peripheral neuropathy. Invest. Ophthalmol. Vis. Sci. 2019;60(9):4731.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the association between the concentration of tear film substance P and diabetic peripheral neuropathy (DPN) in type1 and type 2 diabetes.
A group of 43 individuals with type 1 diabetes, 26 with type 2 diabetes and 36 age-matched healthy controls were enrolled. The presence and severity of peripheral neuropathy was assessed using the Total Neuropathy Score. The concentration of substance P in flush tears was measured by ELISA and corneal nerve fibers were measured using in vivo corneal confocal microscopy. Corneal nerve fibers in the central cornea (C) and the inferior whorl (IW) were measured for nerve fiber length (CNFL; IWNFL), fiber density (CNFD; IWNFD), branch density (CNBD; IWNBD), total branch density (CTBD; IWTBD) and nerve fractal dimension (CNFrD; IWNFrD). One-way ANOVA or Kruskal-Wallis were used to assess differences between groups.
In type 1 diabetes, median [IQR] tear film substance P concentrations was significantly reduced in those with DPN, (130.4 [74-679] pg/mL) compared to controls (714.3 [372-1464] pg/mL, P = 0.01) and those without DPN (849.4 [84.5-1803] pg/mL, P = 0.02). In type 2 diabetes, there was no difference between diabetic patients and controls, regardless of neuropathic status. In type 1 diabetes in those with DPN, the mean CNFD (fibers/mm2; 28.8 ± 4.71 vs. 19.22 ± 5.43, P < 0.001) and IWL (mm/mm2; 17.03 ± 2.82 vs. 10.41 ± 3.98, P < 0.001) were significantly reduced compared to controls, and the mean CNFD (fibers/mm2; 24.45 ± 5.27 vs. 19.22 ± 5.43, P = 0.005) and IWFrD (1.47 ± 0.03 vs. 1.42 ± 0.05, P < 0.001) were significantly reduced compared in those without DPN. Furthermore, a significant reduction was also found those without DPN and controls in mean CNFD (fibers/mm2; 28.8 ± 4.71 vs. 24.45 ± 5.27, P = 0.009). In type 2 diabetes in those with DPN, the mean CNFD (fibers/mm2; 27.87 ± 5.21 vs. 21.73 ± 4.53, P = 0.009) and IWL (mm/mm2; 16.49 ± 2.96 vs. 12.62 ± 3.08, P = 0.03) were significantly reduced compared to control subjects only.
The concentration of substance P in tears is reduced in type 1 with DPN only, although corneal nerve physiology is changed with type1 and type 2 DPN. This may indicate a different effect of type 1 and type 2 diabetes on nerve biochemistry.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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