Age as an Independent Risk Factor for Diabetic Peripheral Neuropathy in Chinese Patients with Type 2 Diabetes

Abstract

Type 2 diabetes mellitus (T2DM) is more prevalent in aging populations. Older adults with diabetes have higher rates of macro and micro vascular complications. Our study assessed whether age is an independent factor for both large and small nerve dysfunctions in Chinese patients with T2DM. This cross-sectional study involved a total of 950 patients with type 2 diabetes (mean age: 60.01±12.30 years). Diabetic peripheral neuropathy (DPN) was assessed according to clinical symptoms and physical examinations by using neuropathy symptom score (NSS), the neuropathy disability score (NDS), Michigan Neuropathy Screening Instrument (MNSI score), vibration perception threshold (VPT) and SUDOSCAN test. By using independent logistic regression model, we showed that age was an independent risk factor of DPN (odds ratio [OR] = 1.036, 95% confidence interval [CI] 1.018-1.054, P< 0.01). T2DM patients over 71 years had a higher risk of DPN determined by using NSS/NDS (OR= 2.087; 95% CI 1.112-3.918; P <0.05), MNSI (OR=1.922; 95% CI 1.136-3.252; P<0.05), VPT (OR=3.452; 95%CI 1.052-11.332; P<0.05) and SUDOSCAN (OR=1.922; 95%CI 1.136-3.252; P<0.05) as diagnostic criteria respectively. The results of spline analysis showed a non-linearly positive association between age and OR of DPN. Individuals with 40, 50, 60, and 70 years old had LnOR of 1.22 (95%CI: 0.44- 2.00), 1.79(95%CI: 0.67- 2.91), 2.29 (95% CI: 0.98- 3.59), and 2.67(95% CI: 1.38-3.96) in DPN risk compared to T2DM patients with 19 years old, respectively. All of the above results in our study suggested age as an independent risk factor for the development of diabetic neuropathy in T2DM patients is significantly associated with the occurrence of both small and large nerve dysfunction, independent of other risk factors.

Full text

http://dx.doi.org/10.14336/AD.2018.0618
*Correspondence should be addressed to: Dr. Bin Lu (Email: binlu@fudan.edu.cn) and Yiming Li (email: yimingli@fudan.edu.cn),
Department of Endocrinology and Metabolism, Huashan Hospital, Fudan University, Shanghai, China. #These authors contributed equally
to this work.
Copyright: © 2018 Mao F et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
ISSN: 2152-5250 592
Original Article
Age as an Independent Risk Factor for Diabetic
Peripheral Neuropathy in Chinese Patients with Type 2
Diabetes
Fei Mao1, #, Xiaoming Zhu1, #, Siying Liu1, Xiaona Qiao1, Hangping Zheng1, Bin Lu1,*, Yiming
Li1, 2*
1Department of Endocrinology and Metabolism, Huashan Hospital, Fudan University, Shanghai, China
2Department of Endocrinology and Metabolism, Jing’an District Center Hospital of Shanghai, China
[Received March 12, 2018; Revised May 3, 2018; Accepted June 18, 2018]
ABSTRACT: Type 2 diabetes mellitus (T2DM) is more prevalent in aging populations. Older adults with diabetes
have higher rates of macro and micro vascular complications. Our study assessed whether age is an independent
factor for both large and small nerve dysfunctions in Chinese patients with T2DM. This cross-sectional study
involved a total of 950 patients with type 2 diabetes (mean age: 60.01±12.30 years). Diabetic peripheral
neuropathy (DPN) was assessed according to clinical symptoms and physical examinations by using neuropathy
symptom score (NSS), the neuropathy disability score (NDS), Michigan Neuropathy Screening Instrument (MNSI
score), vibration perception threshold (VPT) and SUDOSCAN test. By using independent logistic regression
model, we showed that age was an independent risk factor of DPN (odds ratio [OR] = 1.036, 95% confidence
interval [CI] 1.018-1.054, P< 0.01). T2DM patients over 71 years had a higher risk of DPN determined by using
NSS/NDS (OR= 2.087; 95% CI 1.112-3.918; P <0.05), MNSI (OR=1.922; 95% CI 1.136-3.252; P<0.05), VPT
(OR=3.452; 95%CI 1.052-11.332; P<0.05) and SUDOSCAN (OR=1.922; 95%CI 1.136-3.252; P<0.05) as
diagnostic criteria respectively. The results of spline analysis showed a non-linearly positive association between
age and OR of DPN. Individuals with 40, 50, 60, and 70 years old had LnOR of 1.22 (95%CI: 0.44- 2.00),
1.79(95%CI: 0.67- 2.91), 2.29 (95% CI: 0.98- 3.59), and 2.67(95% CI: 1.38-3.96) in DPN risk compared to T2DM
patients with 19 years old, respectively. All of the above results in our study suggested age as an independent risk
factor for the development of diabetic neuropathy in T2DM patients is significantly associated with the
occurrence of both small and large nerve dysfunction, independent of other risk factors.
Key words: Age, T2DM, DPN, risk factor
Diabetes mellitus (DM) is a common metabolic disorder
closely associated with chronic macro-micro vascular
complications (WHO 2016). Among a series of chronic
microvascular complications, diabetic peripheral
neuropathy (DPN) is very common [1-3]. The typical
DPN is a chronic, symmetrical, length-dependent
sensorimotor polyneuropathy [3]. Up to 50% of patients
experience typical manifestations consist of a series of
sensory symptoms, which could be assessed by several
traditional questionnaires as easy screening methods in
everyday clinic [4-6].
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Mao F., et al Age as an independent risk factor for DPN in T2DM patients
Aging and Disease • Volume 10, Number 3, June 2019 593
Though the mechanism of DPN still remains unclear,
it has already been proposed that inflammation, oxidative
stress, and mitochondrial dysfunction are three main
alterations involved in the pathologic changes of DPN [7].
All of these alterations are related to the process of aging
[8]. DPN has been testified to be associated with a number
of modifiable and non-modifiable risk factors [9-12]. Age
as the most evaluated non-modifiable risk factor in the
majority of epidemiological studies of DPN, has been
found highly correlated with the incidence of DPN in
T2DM patients [8].
Previous studies mainly used traditional screening
methods as well as clinical golden diagnostic method
NCS as criteria in diagnosing DPN [13]. However, an
accurate assessment of small fiber damage in diabetic
patients has not evolved in parallel with that of large fiber
damage[13]. The aim of our study was to assess whether
age is an independent factor for the occurrence of DPN
including both small and large nerve dysfunction to prove
more sufficient evidence for early screening of DPN in
diabetic patients in elder patients.
MATERIALS AND METHODS
Study population
The study was conducted in Huashan hospital, Shanghai
from September 2014 to September 2015. The ethics
committee of Hua Shan Hospital approved the study.
Voluntary outpatients diagnosed with type 2 diabetes
between 18 and 80 years of age, with or without
symptoms of neuropathy, were continually enrolled in the
study. Exclusion criteria included undiagnosed
hyperglycemia, T1DM patients, those under treatment
with drugs that could have an effect on the sympathetic
system such as beta blockers and antineoplastic drugs,
implantation of electrical implantable devices, history of
seizures or epilepsy, lumbar sciatic nerve lesion, severe
varices of the lower limbs, other metabolic diseases
including thyroid disease or vitamin B12 deficiency, and
any other advanced systemic condition including severe
hepatic and renal dysfunction [14, 15].
Physical examination
One trained nurse examined all the patients and recorded
the results. Basic physical characteristics were recorded
including height, weight, waist and hip circumference
measured by using standard methods. Body mass index
(BMI) and waist hip ratio (WHR) were calculated. Blood
pressure was recorded in the supine position after 5
minutes of rest. Medical history (diabetes, hypertension,
dyslipidemia, cardiovascular disease and other) was
recorded completely for each patient.
Laboratory examination
Blood samples were collected after at least 8 hours of
fasting. Plasma HbA1c level was determined by high-
pressure liquid chromatography and liquid enzymatic
assay. Serum total cholesterol (TC), triglyceride, high-
density lipoprotein (HDL-C) cholesterol, triglycerides
(TG), high-density lipoprotein cholesterol (HDL-C), low-
density lipoprotein cholesterol (LDL-C) was measured by
using an automatic analyzer (AU640; Olympus
Corporation, Tokyo, Japan).
Peripheral neuropathy examination
Symptoms and signs of lower limbs were recorded
respectively. The assessments of the DPN were performed
by one expert nurse using three different questionnaires
including neuropathy symptom score (NSS), the
neuropathy disability score (NDS) and Michigan
Neuropathy Screening Instrument (MNSI score). A
composite score was calculated separately for neuropathic
symptoms using NSS score questionnaire and for clinical
examination using NDS score. Neurological symptoms
and signs based on the neuropathy symptom score (NSS)
and the neuropathy disability scores (NDS) were
evaluated. Neurological symptoms included burning,
numbness, tingling, fatigue, cramping or aching, and
neurological signs included vibration sense, pain,
temperature sensation and ankle reflex.
MNSI score consists of two parts: The appearance of
the feet (deformity, dry skin, callus, infection or fissures)
and examination of foot ulceration, ankle reflex and
vibration perception with a 128 Hz tuning fork.
Evaluation of each parameter was made at both sides with
a maximum score of 8 points.
Vibration perception threshold (VPT) test
Vibration perception threshold was measured by the same
technician by using a neuro-thesiometer (Bio-
Thesiometer; Bio-Medical Instrument Co., Newbury
Ohio). Before testing, skin temperature of each patient
was examined by a nurse. Then, the stimulus of neuro-
thesiometer was applied to the great toe with the probe
balanced vertically on the pulp of the toe on each side.
Patients were requested to indicate when vibration
sensation was first perceived. Stimulus strength was
gradually increased from null intensity to a value in
voltage at which the subject first detected vibration. The
whole testing procedure was carried out with the subject’s
eyes closed. Both feet were tested three times in a random
order and the VPT for each foot was determined as the
average value of the three measurements calculated in
volts. A ‘null stimulus’ trial was added before the testing

Mao F., et al Age as an independent risk factor for DPN in T2DM patients
Aging and Disease • Volume 10, Number 3, June 2019 594
to ensure the subject’s adherence and understanding. The
whole testing generally required less than 3 min.
Table 1. Baseline characteristics of 950 patients of T2DM
enrolled in the study.
Clinical characteristics
Mean ± SD
Age (years)
60.01±12.30
Male/ Female
555/395
Duration of T2DM (years)
8.85±7.33
SBP (mmHg)
128.69±13.63
DBP (mmHg)
80.27±7.89
HbA1c (%)
8.02±1.88
BMI (kg/m2)
24.43±3.59
Waist circumference (cm)
89.92±10.71
Hip circumference (cm)
96.61±6.62
WHR
0.93±0.07
Smokers (N, %)
215 (22.5)
Alcoholic (N, %)
126 (13.3%)
CHO (mmol/L)
4.48±1.23
HDL-C (mmol/L)
1.06±0.37
TG (mmol/L)
1.91±1.93
LDL-C (mmol/L)
2.54±0.88
NSS score
2.86±2.71
NDS score
2.85±2.62
VPT(V)
12.07±8.03
Foot ESC (µS)
62.25±19.28
Hand ESC (µS)
62.45±17.58
Data are means (SD), percentage (%);
T2DM, type 2 diabetes mellitus; BMI, body mass index; SBP, systolic
blood pressure; DBP, dilated blood pressure; DPN, diabetic peripheral
neuropathy; WHR, waist-hip ratio; HbA1c, glycated hemoglobin; LDL-
C, low-density lipoprotein cholesterol; HDL-C, high-density lipoprotein
cholesterol; CHO, cholesterol; TG, triglyceride; NSS, neuropathy
symptom score; NDS, neuropathy disability score; MNSI, Michigan
Neuropathy Screening Instrument; VPT, vibration perception threshold;
ESC, electrochemical skin conductance; P-value was calculated after
adjustment for age, sex except for itself. *P<0.05; ** P <0.01.
SUDOSCAN test procedure
The SUDOSCAN device is composed of two sets of
electrodes for the feet and hands, both of which are
connected to a computer for recording and data analysis.
The whole process of the test is non-invasive, and no
special preparation is required. Patients only need to place
the palms of their hands and the soles of their feet on the
electrodes for 2 to 3 minutes and a low-voltage (<4V)
electrical current stimulus will be applied by the device
automatically [16]. The device can measure
electrochemical skin conductance values expressed in
micro-Siemens (μS) for the hands and the feet (both right
and left sides). We used the mean of left and right ESC
values for statistical analysis [16].
Diagnostic criteria of DPN
The diagnostic criterion of DPN was a MNSI examination
score of > 2 as previously reported [17]. In this study, we
also used other diagnostic criteria of DPN including
NSS/NDS score [18], VPT [19] and SUDOSCAN [16].
NSS/NDS scores: Patient with an NSS of 3–5 points
were considered with mild neuropathy signs, 6–8 points
as medium neuropathy signs and 9–10 points as severe
neuropathy signs. DPN was diagnosed with an NDS score
of ≥ 6, or an NDS score of 3–5 associated with an NSS
score of ≥ 5. For VPT, we used a threshold of 15V as the
cut-off for diagnosis of DPN in this study. As for the
diagnostic criteria of SUDOSCAN test, we used 60 μS of
mean feet ESC as the cut-off for diagnosis of DPN
according to previous studies.
Statistical analysis
Data are presented as means ± SD for normally distributed
variables and as median (interquartile range) for variables
with a skewed distribution. Parity and gender, which were
analyzed by Chi-square distribution in Table 2.
Differences between groups were examined by
independent-sample t tests for normally distributed
variables and Mann-Whitney U-test for non-normally
distributed data. Differences in offspring parity and sex
distribution were examined by Chi-square test. Logistic
regressions were used to estimate the odds ratio of DPN
in each age group using the lowest group as the reference
category adjusting for other covariates. Considering that
the association between age and DPN risk might be
nonlinear, restricted cubic spline (RCS) analysis was used
to describe nonlinear relationships between the
continuous age and the DPN risk. The RCS analysis uses
piecewise cubic polynomials that are connected across
different intervals of a continuous variable. We chose 3
knots at quantiles 0.050, 0.500 and 0.95. In RCS analysis,
the least value of age was used as the referent, and the ORs
of all other age versus the referent value were calculated
and plotted against their respective age.
RESULTS
In this study, a total number of 950 patients with type 2
diabetes were enrolled continuously (including 563 males

Mao F., et al Age as an independent risk factor for DPN in T2DM patients
Aging and Disease • Volume 10, Number 3, June 2019 595
and 387 females). Amongst these 950 patients with type 2
diabetes (mean age: 60.01±12.30 years, mean duration of
type 2 diabetes: 8.85±7.33 years, mean HbA1C% level:
8.02±1.88 %). Clinical and biochemical characteristics of
the 950 patients are described in Table 1. We divided the
patients into DPN and non-DPN groups by using MNSI
score as diagnostic criteria as indicated before (Table 2).
T2DM patients in the study with DPN diagnosed by
MNSI are older (P< 0.01), have longer duration of T2DM
(P< 0.001), higher systolic blood pressure (P<0.001),
higher NSS score (P<0.001), higher NDS score (P<0.001)
and MNSI score (P<0.001).
Table 2. Characteristics of 950 T2DM patients enrolled in the study divided by DPN diagnosed by
MNSI score.
Clinical characteristics
With DPN
（N=264）
Without DPN
(N=686)
P
Age (years)
63.78±10.91
57.73±12.47
0.000**
Male/Female
157/107
398/288
0.069
Duration of T2DM (years)
11.10±8.23
7.81±6.62
0.000**
SB P(mmHg)
131.82±15.33
127.81±13.10
0.000**
DBP (mmHg)
80.52±7.61
80.20±8.08
0.619
BMI (kg/m2)
24.46±3.39
24.36±3.63
0.741
Waist circumference (cm)
90.74±9.95
89.71±10.94
0.238
Hip circumference (cm)
96.91±6.89
96.50±7.85
0.517
HbA1c (%)
8.19±1.81
8.05±1.97
0.400
Smokers (%)
56(56/200)
147(147/573)
0.515
Alcoholic (%)
23(23/200)
93(93/573)
0.134
MNSI score
5.54±2.11
1.93±1.59
0.000**
NSS score
4.05±2.76
2.50±2.58
0.000**
NDS score
5.59±2.17
1.92±2.04
0.000**
VPT (V)
17.11±10.66
10.39±6.13
0.000**
Foot ESC (µS)
53.49±22.69
65.52±17.14
0.000**
Hand ESC (µS)
55.86±19.21
64.76±16.67
0.000**
Data are means (SD), percentage (%);
T2DM, type 2 diabetes mellitus; BMI, body mass index; SBP, systolic blood pressure; DBP, dilated blood pressure; DPN,
diabetic peripheral neuropathy; WHR, waist-hip ratio; HbA1c, glycated hemoglobin; LDL-C, low-density lipoprotein
cholesterol; HDL-C, high-density lipoprotein cholesterol; CHO, cholesterol; TG, triglyceride; NSS, neuropathy symptom
score; NDS, neuropathy disability score; MNSI, Michigan Neuropathy Screening Instrument; VPT, vibration perception
threshold; ESC, electrochemical skin conductance; P-value was calculated after adjustment for age, sex except for itself.
*P<0.05; ** P <0.01;

Mao F., et al Age as an independent risk factor for DPN in T2DM patients
Aging and Disease • Volume 10, Number 3, June 2019 596
Table 3. Characteristics of 950 T2DM patients enrolled in the study stratified by four age groups (≤50,
51-60, 61-70, ≥71).
≤50
(N=183)
51-60
(N=269)
61-70
(N=308)
≥71
(N=180)
P
Male (%)
128 (69.95%)
167 (62.08%)
167 (54.22%)
93 (51.67%)
0.001**
Duration of T2DM
(years)
4.73±5.11
7.57±5.42
10.28±7.85
12.89±8.32
0.000**
SBP (mmHg)
125.09±11.77
126.46±14.09
130.62±13.46
132.42±13.47
0.000**
DBP (mmHg)
81.03±7.92
80.88±7.97
80.26±7.80
78.34±7.62
0.004**
BMI
25.77±4.11
23.84±3.32
24.39±3.36
24.05±3.48
0.000**
WHR
0.93±0.08
0.93±0.06
0.92±0.07
0.93±0.09
0.952
NSS
2.24±2.59
2.82±2.80
3.13±2.69
3.11±2.61
0.003**
NDS
2.15±2.37
2.62±2.53
3.16±2.67
3.64±2.68
0.000**
MNSI
1.14±1.30
1.39±1.27
1.86±1.45
2.16±1.48
0.000**
VPT (V)
8.34±6.78
11.11±7.50
13.47±7.97
17.18±7.91
0.000**
Foot ESC (µS)
65.00±19.85
65.32±17.78
62.11±18.67
55.35±20.12
0.000**
Hand ESC (µS)
64.91±17.89
63.47±16.04
62.45±17.82
58.29±18.19
0.002**
HbA1c (%)
8.39±2.11
8.031±1.90
7.98±1.85
7.67±1.61
0.009**
T2DM, type 2 diabetes mellitus; BMI, body mass index; SBP, systolic blood pressure; DBP, dilated blood pressure; DPN, diabetic
peripheral neuropathy; WHR, waist-hip ratio; HbA1c, glycated hemoglobin; NSS, neuropathy symptom score; NDS, neuropathy
disability score; MNSI, Michigan Neuropathy Screening Instrument; VPT, vibration perception threshold; ESC, electrochemical
skin conductance;
P-value was calculated after adjustment for age, sex except for itself. *P<0.05; ** P <0.01.
To understand the influence of age on the incidence
of DPN, we further analyzed all clinical characteristics in
T2DM patients stratified by age of ≤50, 51-60, 61-70, ≥
71 (Table 3). As we could see from the table, T2DM aging
above 71 have the longest duration of T2DM (P< 0.01),
highest systolic blood pressure level (P<0.01) and highest
scores including NSS (P< 0.01), NDS (P<0.01), highest
VPT level (P< 0.01), lowest hands (P<0.01）and feet
ESC levels (P<0.01).
We used independent logistic regression model to
quantify significant risk factors for DPN. Multivariate
logistic regression analysis showed that clinical factors
including age (odds ratio [OR] = 1.036, 95% confidence
interval [CI] 1.018-1.054, P< 0.01), duration of T2DM
(OR= 1.034, 95% CI 1.007-1.062, P< 0.01), HbA1c level
(OR= 1.121, 95% CI 1.018-1.054, P< 0.01) and systolic
blood pressure (OR= 1.017, 95% CI 1.003-1.032, P<
0.05) were independent risk factors of DPN (Table 4).
After adjusting for duration of T2DM, gender,
smoking, drinking, SBP, BMI, HbA1c, as compared with
T2DM patients aged under 50 years old (reference),
T2DM patients aged over 71 years had a higher risk of
DPN determined by using NSS/NDS (OR= 2.087; 95% CI
1.112-3.918; P < 0.05), MNSI (OR=1.922; 95% CI 1.136-
3.252; P <0.05), VPT (OR=3.452; 95% CI 1.052-11.332;
P<0.05) and SUDOSCAN (OR=1.922; 95% CI 1.136-
3.252; P<0.05) as diagnostic criteria respectively (Table
5). However, both T2DM patients aged between 50 and
60 years old as well as aged between 60 and 70 didn’t
show significant higher risk of DPN by different
diagnostic criteria (Table 5).
We next used spline analysis to determine the risk
association between age and OR of DPN in patients with
T2DM. On spline analysis, the age level was non-linearly
associated with OR of DPN comparing patients of 19
years old, and OR of DPN significantly increased with age
(As seen in Figure 1). Individuals with 40, 50, 60, and 70

Mao F., et al Age as an independent risk factor for DPN in T2DM patients
Aging and Disease • Volume 10, Number 3, June 2019 597
years old had LnOR of 1.22 (95% CI: 0.44, 2.00), 1.79
(95% CI: 0.67, 2.91), 2.29 (95% CI: 0.98, 3.59), and 2.67 (95% CI: 1.38-3.96) in DPN risk compared to T2DM
patients with 19 years old, respectively.
Figure 1. Adjusted dose-response association between age (years) and DPN diagnosed by different criteria including NSS/NDS
score, MNSI score, VPT and SUDOSCAN. Adjusted dose-response association between age (years) and the presence of DPN with
three knots located at the 5th, 50th , and 95th percentiles. Y-axis represents the Ln (Odds Ratio) to present DPN for any value of age
compared to individuals with 19 years old. The red line is the adjusted curve and dashed lines are 95 percent confidence intervals. A)
Adjusted dose-response association between age (years) and DPN diagnosed by MNSI score. B) Adjusted dose-response association
between age (years) and DPN diagnosed by NSS/NDS score. C) Adjusted dose-response association between age (years) and DPN
diagnosed by VPT value. D) Adjusted dose-response association between age (years) and DPN diagnosed by SUDOSCAN ESC value
DISCUSSION
Diabetic neuropathy is a well-known microvascular
complication of type 2 diabetes mellitus attributed to
chronic hyperglycemia and is defined as the presence of
peripheral nerve dysfunction in diabetics after exclusion
of other causes [20, 21]. No study has ever reported the
possible relationship between age and small fibre
neuropathy which is indicated in early stage of diabetic
nerve dysfunction. Our results in this study demonstrated
that increasing age is independently associated with an
increased risk of developing DPN in patients with T2DM
by using different diagnostic criteria including both
traditional scoring methods, VPT screening as well as the
newly developed sudomotor device. We found that age is
non-linearly positively associated with OR of DPN. This
study is the first cross-sectional study carried out to
analyze the risk factor of age in Chinese T2DM patients
by using SUDOSCAN targeting at small nerve function
and VPT targeting at large nerve function.

Mao F., et al Age as an independent risk factor for DPN in T2DM patients
Aging and Disease • Volume 10, Number 3, June 2019 598
Table 4. Multivariate logistic regression model of clinical factors and DPN diagnosed by MNSI score.
Clinical factors
B
SE
OR
LCI
UCI
P
Age (years)
0.035
0.009
1.036
1.018
1.054
0.000**
Duration of T2DM (years)
0.034
0.014
1.034
1.007
1.062
0.015*
Gender
-0.149
0.198
0.862
0.585
1.270
0.452
SBP（mmHg）
0.017
0.007
1.017
1.003
1.032
0.015*
BMI (kg/m2)
0.014
0.028
1.014
0.960
1.071
0.618
HbA1c (%)
0.114
0.051
1.121
1.014
1.240
0.026*
T2DM, type 2 diabetes mellitus; BMI, body mass index; SBP, systolic blood pressure; DPN, diabetic peripheral neuropathy;
HbA1c, glycated hemoglobin; SE, standard error; OR, odds ratio; CI, confidence interval; UCI, upper confidence interval; LCI,
lower confidence interval
P-value was calculated after adjustment for age, sex except for itself. *P<0.05; ** P <0.01.
Previous studies have already showed that sensory
neuropathy is more common in long-standing diabetic
subjects and is strongly related to age at diagnosis [10, 11,
22]. In year 2014, Anil Bhansali et al. [9] showed that age
(OR 1.02, 95% CI 1.01–1.03, P < 0.001) was significantly
associated with diabetic microvascular complications
including diabetic neuropathy. Dehong Cai et al. [11]also
showed that the prevalence of DPN in patients with age of
20–34, 35–49, 50–64 and ≥65 was 8.4%, 22.7%, 33.0%
and 42.4%, respectively, which indicated a significant
difference between age and the incidence of neuropathy
(p<0.001). The study confirmed that age (OR: 1.016,
95%CI: 1.008, 1.024) was significantly associated with
the development of DPN. Romulus Timar et al. [22] and
their team showed in their study that the prevalence of
DPN according to MNSI score was 28.8%, being
significantly and positively correlated with higher age (65
vs 59 years; P=0.001) indicating that age influences the
presence of DN, independent of other risk factors. As has
been reported in many different animal studies, peripheral
neuropathy which is detected by nerve conduction
velocity, has been proved to be aging-related[23]. As
nerve conduction velocity remains unchanged during
adulthood of mice, it begins to decline after that. Further
morphologic examination shows that there is a gradual
decline in the number and density of both myelinated and
unmyelinated nerve fibers in mice starting from 12–20
months old. And from 20 months on, there is
approximately 50% loss of myelinated fibers and 35%
loss of unmyelinated fibers in mice [24].
Table 5. Adjusted odds ratio of T2DM patients with DPN stratified by four age groups (≤50, 51-60, 61-70, ≥71)
by using different diagnostic methods.
Age
NSS/NDS P value
MNSI P value
VPT P value
SUDOSCAN P value
≤50
Ref
Ref
Ref
Ref
51-60
1.740
(1.011-2.996)
0.046*
1.270
(0.810-1.992)
0.298
1.371
(0.430-4.376)
0.594
1.270
(0.810-1.992)
0.298
61-70
1.536
(0.880-2.681)
0.131
1.270
(0.804-2.005)
0.305
1.598
(0.505-5.060)
0.426
1.270
(0.780-2.218)
0.305
≥71
2.087
(1.112-3.918)
0.022*
1.922
(1.136-3.252)
0.015*
3.452
(1.052-11.332)
0.041*
1.922
(1.136-3.252)
0.015*
T2DM, type 2 diabetes mellitus; DPN, diabetic peripheral neuropathy; NSS, neuropathy symptom score; NDS, neuropathy disability score;
MNSI, Michigan Neuropathy Screening Instrument; VPT, vibration perception threshold; SE, standard error; OR, odds ratio; CI, confid ence
interval; UCI, upper confidence interval; LCI, lower confidence interval;
P for One-way ANOVA. P-value was calculated after adjustment for duration of T2DM, gender, SBP, BMI, HbA1c.
*P<0.05.

Mao F., et al Age as an independent risk factor for DPN in T2DM patients
Aging and Disease • Volume 10, Number 3, June 2019 599
The molecular basis of aging and aging-related
changes is still not completely understood. It is generally
accepted that aging is driven by time accompanied
accumulation of molecular and cellular damage. As in
diabetic peripheral neuropathy, damage to both large and
small fibers can be caused by axonal damage or
demyelination.
The limitations of this study should be fully
addressed. First of all, the study was conducted in
Huashan hospital and T2DM patients recruited were not
society based, which could lead to bias since those
patients were mostly middle to old age. Secondly, in this
cross-sectional study, we used relatively subjective
methods to evaluate large nerve dysfunction such as VPT,
traditional scoring methods including NSS, NDS and
MNSI scores instead of electromyography which has been
proved as golden standard in clinical use. Since
electromyography is more time consuming and expensive
compared to those screening methods, we didn’t perform
it in this study. Therefore, further study with more
accurate electrophysiological methods could be
considered as diagnostic methods in determining the
association between age and the incidence of DPN.
As we know, the management of diabetic
polyneuropathy includes three main elements: normal
blood glucose level, foot care, and treatment of pain
according to the guideline of management[6]. The results
of this study, demonstrating that advancing age is
associated with an increased risk of developing DPN in
T2DM patients, emphasize the necessity of an intensified,
proactive screening for DPN in elderly patients with
T2DM.
Acknowledgments
The present study was supported by grants from the
National Natural Science Foundation of China
(81370884, to B Lu), the Shanghai New Excellent Youth
Program (XYQ2013120, to B Lu), Fudan Zhuoxue
Project (to B Lu), Pudong program from Pudong
Municipal Commission of Health and Family Planning
(PW2014D-2, to B Lu), and Shanghai Science and
Technology Committee Program (14411962200, to YM
Li).
Disclosure
The authors declare no conflict of interest.
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