Diabetic Peripheral Neuropathies in Type 2 Diabetes at Brazzaville University Hospital: Prevalence and Associated Factors ()
1. Introduction
Diabetes mellitus (DM) is a major public health issue globally. According to the International Diabetes Federation (IDF), an estimated 588.7 million people had diabetes worldwide in 2023, including 24.6 million in Africa. These figures are projected to rise to 852.5 million globally and 59.5 million in Africa by 2050 [1]. Consequently, diabetes represents an escalating burden on global health systems [2].
Type 2 diabetes mellitus (T2DM) is the most common form, accounting for approximately 96% of all diabetes cases [3]. It is a chronic condition with various complications, particularly microvascular and macrovascular. Among microvascular complications, diabetic neuropathies (DN) are frequent. DN may involve the somatic peripheral nervous system, resulting in peripheral neuropathy (PN), or the autonomic nervous system, leading to autonomic neuropathy (AN). Approximately 50% of diabetic patients develop neuropathy during their lifetime, making T2DM the leading global cause of PN [4]. Recent studies in sub-Saharan Africa have reported a high prevalence of diabetic peripheral neuropathy (DPN) ranging from 34.8% to 65.8%. Multiple associated factors have been identified, including diabetic imbalance, diabetic retinopathy, and dyslipidemia [5] [6].
DPN is defined by the presence of symptoms and/or electrophysiological evidence of peripheral nerve dysfunction associated with diabetes, after excluding other causes [7]. Its clinical presentation is variable, ranging from painful, paresthesia, or motor symptoms to asymptomatic or subclinical forms, often discovered incidentally. This heterogeneity complicates early diagnosis, although subclinical forms carry the same risks of severe complications [8].
DPN significatively contributes to the development of foot ulcers and Charcot arthropathy, making it a leading cause of lower-limb amputations worldwide [9]. In Congo, the estimated average cost of managing diabetes complications was 519,461 FCFA (approximatively 865,77 USD) in 2023 [10].
Early diagnosis of DPN is therefore a public health priority. Diagnosis is primarily clinical, but ENMG provides valuable support, especially for detecting subclinical cases. However, few studies have integrated systematic electrophysiological evaluation in the context of diabetes.
This study aimed to estimate the prevalence of DPN and identify associated factors among T2DM patients at Brazzaville University Hospital.
2. Patients and Methods
2.1. Study Design and Setting
This cross-sectional analytical study was conducted over six months, from February 1 to July 31, 2024. It was carried out in the outpatient metabolic and endocrine disease unit and the clinical neurophysiology laboratory of the Neurology Department at Brazzaville University Hospital.
2.2. Participants
The study population included all T2DM patients followed at the outpatient metabolic and endocrine disease unit. Participants were recruited exhaustively. Inclusion criteria were age ≥ 18 years, documented T2DM, available glycosylated hemoglobin (HbA1c) value, ENMG assessment, and signed informed consent. Patients with a known cause of peripheral neuropathy (e.g., chronic alcohol use, HIV infection, malignancy, systemic diseases, chemotherapy, neurotoxic drugs), foot deformities, ulcerations, or amputation preventing ENMG, and those with cognitive or psychiatric disorders impairing consent and comprehension were excluded.
2.3. Data Collection
Data were collected using a standardized questionnaire. Information included sociodemographic data, medical and diabetes history, and treatment adherence assessed by the Morisky Medication Adherence Scale. Neurological evaluation included DN4 screening for neuropathic pain, measurement of the ankle-brachial index (ABI) via Doppler after 30 minutes of supine rest, and ENMG.
2.4. ENMG Protocol
Examinations were scheduled according to patient availability and conducted under optimal technical conditions (controlled skin temperature at 37°C). The following nerves were explored: median and ulnar nerves (motor and sensory components) in the upper limbs; common fibular, tibial (motor), and sural (sensory) nerves in the lower limbs. Standardized techniques were used for nerve stimulation and recording. Needle EMG was not performed due to its invasive nature. Motor parameters included distal/proximal latencies and amplitudes, conduction velocity, and F-wave latency. Sensory parameters included sensory latency, amplitude, and conduction velocity. Interpretation followed University Hospital of Brazzaville standards and ENFS/PNS guidelines [11] [12].
2.5. Assessment Criteria
DPN was categorized as electro-clinical (presence of clinical signs and ENMG abnormalities), clinical (presence of clinical signs only), subclinical (presence of ENMG abnormalities only), or none (absent of both clinical and ENMG findings).
According to the recommendations of the American Diabetes Association (ADA), diabetes control was defined as reaching a glycosylated hemoglobin (HbA1c) level of ≤7%. The ABI was interpreted as follows [13]: >1.30, non-compressible arteries or medial arterial calcification (MAC); 0.90 - 1.30, normal; <0.9, peripheral arterial occlusive disease (PAOD).
2.6. Statistical Analysis
The data were entered into Microsoft Excel and analyzed using Jamovi v2.6.17. Categorical variables were expressed as frequencies and percentages, and continuous variables were expressed as the mean ± standard deviation or the median [interquartile range (IQR)], depending on the results of the Shapiro-Wilk test. Categorical comparisons used the Chi-square or Fisher’s exact test. Continuous data comparisons used a Student’s t-test or a Mann-Whitney test. Multivariate logistic regression was performed to identify factors associated with DPN. Variables with p < 0.20 in the univariate analysis were included in the multivariate model. Model fit was evaluated using the Hosmer and Lemeshow test. The significance threshold was set at p < 0.05.
2.7. Ethical Considerations
All participants provided written informed consent prior to being included in the study. The study protocol was reviewed and approved by the Ethics and Research Committee of the Faculty of Health Sciences at Marien Ngouabi University. All procedures were conducted in accordance with the principles outlined in the Declaration of Helsinki. Patients diagnosed with DPN were referred to the neurology outpatient unit for appropriate management, including optimization of glycemic control, treatment of neuropathic pain, lifestyle advice, and prevention of complications, such as foot ulcers. These patients were subsequently monitored as part of their routine diabetes care.
The authors declare that they have no conflicts of interest related to this study.
3. Results
3.1. Prevalence of DPN
Of the 220 patients with type 2 diabetes mellitus (T2DM) selected, 102 completed clinical and electrophysiological investigations, yielding a participation rate of 46.3%. The remaining 118 patients did not undergo ENMG because they missed their appointment.
DPN was diagnosed in 81 patients, representing a prevalence of 79.4%.
3.2. Sociodemographic and Anthropometric Characteristics
The mean age of patients with DPN was 59.75 ± 9.87 years, ranging from 38 to 82 years old. Of these patients, 56 were women (69.1%) and 25 were men (30.9%), resulting in a male-to-female ratio of 0.44.
Table 1 summarizes occupational status, socioeconomic and education levels.
3.3. Body Mass Index
The mean BMI was 28.2 ± 5.7 kg/m2 (range: 16.8 - 44.1). Patients were evenly distributed among normal weight, overweight, and obese categories (33.3% in each).
3.4. Diabetes History
The median duration of diabetes was 20 months (approximately 1.7 years), and the mean was 56.4 ± 71.5 months (approximately 4.7 ± 6 years). The range was 1 - 384 months.
The ABI was normal in 59.3% of cases and abnormal in 40.7%, with PAOD predominating (63.6%) over MAC (36.4%).
Table 1. Occupational status, socioeconomic and education levels.
|
n |
% |
Occupational status |
|
|
Retired |
26 |
32.1 |
Administrative officer |
12 |
14.8 |
Sales |
10 |
12.3 |
Teacher |
3 |
3.7 |
Farmer |
2 |
2.5 |
Unemployed |
20 |
24.7 |
Others* |
8 |
9.9 |
Socioeconomic level |
|
|
High |
2 |
2.5 |
Medium |
49 |
60.5 |
Low |
30 |
37 |
Education level |
|
|
Primary |
5 |
6.2 |
Secondary |
51 |
62.9 |
Higher |
24 |
29.6 |
None |
1 |
1.2 |
*Others: policeman (n = 2), brewer (n = 1), orderly (n = 1), driver (n = 1), electrician (n = 1), nurse (n = 1) and pastor (n = 1).
Associated complications included nephropathy (12.3%), stroke (8.6%), coronary artery disease (3.7%), and retinopathy (2.5%).
Regarding treatment, 61.7% were on oral antidiabetics (OADs), 19.8% were on insulin, and 18.5% were on both. Treatment adherence was high in 49.4% of patients, moderate in 42% and low in 8.6%.
The mean HbA1c was 8.7% ± 2.1% (range: 5.1-15%). Glycemic control (HbA1c ≤ 7%) was achieved by 19.6% (n = 20) of patients.
3.5. Clinical Features of Peripheral Neuropathy
DPN was clinically suspected in 66 patients (81.5%).
3.5.1. Subjective Complaints
Previous paresthesia was reported by 25.9% of patients. Eighty-one-point five percent of patients had current neuropathic symptoms, including paresthesia (100%), cramps (28.8%), and neuropathic pain (21.2%). Symptoms had persisted for more than six months in 92.4% of patients.
3.5.2. Objective Clinical Signs
Objective clinical signs were present in 33 patients (40.7%). These signs included the absence of osteotendinous reflexes (63.6%), thermal hypoesthesia (63.6%), amyotrophy of the thenar eminence or leg (9.1%), and vibratory hypoesthesia (3%).
3.6. Electrophysiological Characteristics
ENMG confirmed DPN in 54 patients (66.7%). Of the 66 cases suspected clinically cases, ENMG confirmed 81.8%. Twelve patients (18.2%) had no ENMG abnormalities, which suggests small fiber involvement. Conversely, 18,5% of DPN cases were subclinical, presenting only with ENMG abnormalities.
There was no significant association between subjective symptoms and ENMG abnormalities (p = 0.109).
Table 2 presents DPN types identified by ENMG.
Table 2. Types of diabetic peripheral neuropathy identified by ENMG.
|
n |
% |
Mononeuropathy |
47 |
87 |
Carpal tunnel syndrome |
45 |
95.7 |
Symmetrical ulnar sensory neuropathy |
2 |
4.3 |
Polyneuropathy |
20 |
37 |
Topography |
|
|
Four members |
17 |
85 |
Lower limbs |
2 |
10 |
Upper limbs |
1 |
5 |
Type of nerve fibers affected |
|
|
Sensorimotor |
16 |
80 |
Sensory only |
4 |
20 |
Mechanism of injury |
|
|
Axonal damage |
17 |
85 |
Demyelination |
3 |
15 |
Radiculopathies |
10 |
18.5 |
L5 radiculopathy |
7 |
70 |
S1 radiculopathy |
3 |
30 |
Multiple mononeuropathy |
1 |
1.8 |
3.7. Correlation between DPN Types and Clinical Variables
DPN types were significantly associated with diabetes duration (p = 0.001), but not with age, BMI, or HbA1c levels. See Table 3 for detailed results.
3.8. Factors Associated with the Occurrence of DPN
Univariate analysis revealed associations with age (p = 0.009), diabetes duration (p = 0.034), right ABI (p = 0.040), and the Morisky adherence scale (p = 0.002) (see Table 4).
Table 3. Correlation between DPN types and clinical variables.
|
Mean ± SD |
Extremes |
Median |
p-value |
Age (years) |
|
|
|
0.333 |
Subclinical |
60.5 ± 11.2 |
40 - 81 |
62 |
|
Clinical |
55.8 ± 10.4 |
38 - 71 |
54 |
|
Electro-clinical |
60.4 ± 9.4 |
41 - 78 |
60 |
|
Progression time (months) |
|
|
|
0.001 |
Subclinical |
24.1 ± 52.7 |
1 - 240 |
7 |
|
Clinical |
33.8 ± 44.6 |
2 - 120 |
12 |
|
Electro-clinical |
70.5 ± 77.2 |
1 - 384 |
42 |
|
BMI (kg/m2) |
|
|
|
|
Subclinical |
26.5 ± 4.8 |
20.6 - 38.7 |
26.9 |
0.633 |
Clinical |
29.2 ± 5.6 |
19.5 - 44.1 |
27.5 |
|
Electro-clinical |
27.8 ± 6.4 |
18.2 - 41.8 |
26.2 |
|
HbA1c level (%) |
|
|
|
|
Subclinical |
8.5 ± 1.8 |
5.1 - 11.4 |
8.7 |
0.095 |
Clinical |
7.7 ± 1.4 |
6 - 10 |
7.2 |
|
Electro-clinical |
9.1 ± 2.3 |
5.3 - 15 |
8.9 |
|
DPN: diabetic peripheral neuropathy, BMI: body mass index, HbA1c: glycated hemoglobin.
Table 4. Univariate analysis of factors associated with presence of DPN.
|
DPN absent N = 21 |
DPN present N = 81 |
p-value |
Age (years)* |
52.1 ± 11.4 |
59.8 ± 9.9 |
0.009 |
Gender, n (%) |
|
|
|
Male |
7 (33.3) |
25 (30.8) |
1.000 |
Female |
14 (66.6) |
56 (69.1) |
Socioeconomic level, n (%) |
|
|
|
Low |
8 (38) |
30 (37) |
0.073 |
Medium |
10 (47.6) |
49 (60.4) |
High |
3 (14.2) |
2 (2.4) |
Education level, n (%) |
|
|
|
Primary |
- |
5 (6.2) |
0.618 |
Secondary |
14 (66.7) |
51 (63) |
|
Higher |
6 (28.6) |
24 (29.6) |
None |
1 (4.7) |
1 (1.2) |
Diabetes duration (months) |
11.8 ± 20.4 |
56.4 ± 71.5 |
0.034 |
HbA1c rate (%) |
8.5 ± 0.6 |
8.7 ± 5.7 |
0.680 |
Morisky score |
0.3 ± 0.5 |
0.9 ± 1 |
0.002 |
Body mass index (kg/m2) |
28.1 ± 5 |
28.2 ± 5.7 |
0.950 |
Ankle-brachial index (mmHg) |
|
|
|
Left |
1.1 ± 0.2 |
1.1 ± 0.2 |
0.230 |
Right |
1.1 ± 0.1 |
1.0 ± 0.2 |
0.040 |
Arteriopathy, n (%) |
|
|
|
Absent |
16 (76.2) |
48 (59.3) |
0.357 |
PAOD |
3 (14.3) |
21 (25.9) |
MAC |
2 (9.5) |
12 (14.8) |
DPN: diabetic peripheral neuropathy, PAOD: peripheral arterial occlusive disease, MAC: medial arterial calcification. *Mean ± standard deviation.
Five covariates with a p < 0.20 were included in the multivariate logistic regression: age, diabetes duration, right ABI, Morisky score, and sociodemographic level. With 81 events (patients with DPN), the events-per-variable ratio was 16.2, meeting accepted methodological standards. The multivariate logistic regression analysis identified advanced age (OR = 1.069 [95% CI: 1.008 - 1.134]; p = 0.027) and longer diabetes duration (OR = 1.034 [95% CI: 1.002 - 1.066]; p = 0.034) as independent predictors. The other variables were excluded during stepwise selection due to a lack of statistical significance, suggesting that their effects were confounded or not independently associated with the outcome.
4. Discussion
4.1. Prevalence of DPN
The 79.4% prevalence rate observed in our study is higher than the rates reported in INTERPRET-DD study (26.7%) and an African meta-analysis (46%) [14] [15]. The INTERPRET-DD study included 2733 patients with T2DM from 14 countries worldwide. The African meta-analysis involved 33 studies with 269,691 participants. The estimated prevalence in Central Africa was the lowest, at 35.9%. This difference may be explained by the use of ENMG, which identified 18.5% of subclinical cases.
Similar rates were reported in the neurological functional explorations unit at Limoges University Hospital (87.3%) and among elderly patients undergoing ENMG in Tunis (89.4%) [16] [17]. Other studies using clinical criteria report lower prevalence rates ranging from 14.3% to 44% [18] [19]. In Mali, a prevalence of 69.8% was reported when autonomic neuropathies were included [20]. At Brazzaville University Hospital, 93.13% of patients with diabetic foot syndrome had DPN [10].
This variability can be attributed to diagnostic methods, population characteristics, and care quality. However, one study reported no significant geographical variation [21].
4.2. Clinical and Electrical Characteristics of Peripheral Neuropathy
Consistent with its known association in diabetics, carpal tunnel syndrome (87%) was the most frequent form [22]-[25]. The pathophysiological mechanisms include endoneural glucose accumulation, ischemia, and compression due to musculoskeletal alterations [23] [24] [26] [27].
The second most common form was polyneuropathy (37%), which was mainly sensorimotor, axonal, and diffuse, aligning with existing literature [28]-[32]. Oxidative stress appears to be the common pathway for nerve damage induced by hyperglycemia [33]-[35].
The prevalence of neuropathic pain (21.2%) was lower than in other studies (36.8% to 56.7%) [36] [37]. Radiculopathies were rare and difficult to distinguish from common sciatica [38]-[40].
The 18.5% rate of subclinical DPN supports the use of systematic ENMG at diagnosis. Up to 50% of DPN may be asymptomatic, which exposes patients to insensitive foot lesions [41]. The shorter median onset time of seven months underscores the early manifestation of these forms compared to clinical forms, which have median onset times of 12 months for small fibers and 42 months for large fibers. Furthermore, clinical symptoms did not influence ENMG results.
4.3. Factors Associated with the Occurrence of Peripheral Neuropathy
Several factors have been linked to the development of DPN in patients with T2DM [42] [43]. Consistent with prior studies, age and diabetes duration were significantly associated with DPN [14] [18] [21] [44]. Other known risk factors include poor glycemic control, smoking, sedentary behavior, obesity, cardiovascular disease, microalbuminuria, severe ketoacidosis, and retinopathy [14] [18] [19] [21] [42]-[44]. However, in our study, neither ABI abnormalities nor HbA1c level were significantly associated with DPN, despite 40.7% of participants having ABI abnormalities and the mean HbA1c level being 8.7%.
The prevalence of DP increases with diabetes duration, rising from 7% in the first year to 50% after 20 years [45]. This is consistent with reports linking DPN to diabetes durations of over 15 years [31]. The main mechanisms involved in nerve degeneration are chronic oxidative stress and metabolic pathway overload induced by hyperglycemia [46]. Thus, while treatment adherence was not associated with DPN occurrence in the multivariate analysis, it was significantly lower among patients with DPN in the univariate analysis. This reflects the increased risk of poor glycemic control associated with DPN development. Furthermore, these patients had slightly higher mean HbA1c levels, and nearly half of them were taking oral antidiabetics medication.
4.4. Strengths and Limitations
This study has several strengths. First, the systematic use of ENMG enabled the detection of both clinical and subclinical forms of DPN. Second, the rigorous exclusion of alternative causes of neuropathy ensured diagnostic specificity. Conducted in a real-world hospital setting, the study also identified key associated factors, such as age and diabetes duration. However, the cross-sectional design limits causal interpretation, and the relatively small sample size and single-center setting may affect generalizability. Only 102 out of 220 eligible patients completed the full protocol, potentially introducing selection bias. Additionally, this study did not include specific tests for assessing small fibers, such as quantitative sensory testing or skin biopsies, due to the limited availability of these techniques in our setting. Consequently, some cases of small fiber neuropathy may have gone undetected, particularly in patients with normal ENMG results. This limitation may have led to an underestimation of DPN prevalence in the early stages or in its sensory form. Additionally, the lack of longitudinal follow-up for treatment outcomes limits our ability to assess treatment effectiveness.
5. Conclusion
Diabetic peripheral neuropathy is common among patients with type 2 diabetes mellitus (T2DM) at Brazzaville University Hospital, with carpal tunnel syndrome and distal sensorimotor polyneuropathies being the most prevalent forms. The detection of subclinical DPN in nearly 20% of patients underscores the importance of conducting ENMG screenings as soon as diabetes is diagnosed. Age and duration of diabetes are key predictive factors. Early detection and neurological monitoring are crucial to preventing disabling complications.