Pain in diabetic neuropathy case study: whole patient management

Efficient conditioned pain modulation despite pain persistence in painful diabetic neuropathy

Despite persistent clinical pain in patients with painful diabetic neuropathy, longer pain duration was associated with more efficient CPM.

Introduction:

Alleviation of pain, by either medical or surgical therapy, is accompanied by transition from less efficient, or pro-nociceptive, to efficient conditioned pain modulation (CPM). Spontaneous decrease or resolution of pain with disease progression is reported for some patients with painful diabetic neuropathy (PDN).

Objectives:

To explore whether CPM changes similarly in parallel to spontaneous resolution of pain in PDN patients.

Methods:

In this cross-sectional study, thirty-three patients with PDN underwent psychophysical assessment of pain modulation on the forearm, remote from the clinical pain.

Results:

Pain duration was not correlated with neuropathic pain intensity, yet, it correlated with CPM efficiency; patients with longer pain duration had same pain level, but more efficient CPM than those with short-pain duration (ρ = −0.417; P = 0.025, Spearman correlation). Patients with pain more than 2 years (median split) expressed efficient CPM that was not different from that of healthy controls. These patients also had lower temporal summation of pain than the short-pain duration patients group (P < 0.05). The 2 patient groups did not differ in clinical pain characteristics or use of analgesics.

Conclusion:

Pro-nociception, expressed by less efficient CPM and high temporal summation that usually accompanies clinical painful conditions, seems to “normalize” with chronicity of the pain syndrome. This is despite continuing pain, suggesting that pro-nociceptivity in pain syndromes is multifactorial. Because the pain modulation profile affects success of therapy, this suggests that different drugs might express different efficacy pending on duration of the pain in patients with PDN.

Prevalence, discomfort and self-relief behaviours of painful diabetic neuropathy in Taiwan: a cross-sectional study

OBJECTIVES

To explore the prevalence, discomfort, and self-relief behaviours of painful diabetic neuropathy (PDN) among rural community residents with type 2 diabetes.

DESIGN

A community-based, cross-sectional study.

SETTING

This study was part of a longitudinal cohort study of a nurse-led health promotion programme for preventing foot ulceration in Chiayi County, Taiwan.

PARTICIPANTS

Six hundred and twenty-eight community adults with type 2 diabetes participated in this study.

OUTCOME MEASURES

Parameters assessed included peripheral neuropathy, peripheral vasculopathy, glycaemic control and metabolic biomarkers. Statistical analyses included descriptive statistics and a multivariate logistic regression model.

RESULTS

About 30.6% of participants (192/628) had PDN. Factors associated with PDN included an abnormal ankle brachial index (ABI; OR=3.4; 95% CI 1.9 to 6.2; p<0.001), Michigan neuropathy screening index (OR=1.69; 95% CI 1.0 to 2.6; p=0.021), triglyceride level (OR=1.61; 95% CI 1.0 to 2.4; p=0.036) and being female (OR=1.68; 95% CI 1.1 to 2.4; p=0.022). PDN was characterised by uncomfortable feelings of prickling, stinging or burning pain and inexplicable dullness around the base or dorsal areas of the feet, but received little attention or treatment from primary healthcare providers.

CONCLUSIONS

A high prevalence of PDN was found in rural community residents with type 2 diabetes and the healthcare workers provided little attention to, or treatment of, discomfort. It is important to identify high-risk groups with PDN early in order to prevent foot ulceration and reduce the incidence of amputation of the extremities. It is also urgent to develop appropriate treatment and self-relief behaviours to halt or reverse the progression of PDN for this population living in rural areas.

Utility of DN4 questionnaire in assessment of neuropathic pain and its clinical correlations in Turkish patients with diabetes mellitus

AIM

We aimed to assess the utility of DN4 questionnaire (Douleur Neuropathique en 4 questions) to define the frequency and severity of neuropathic pain (NP) and also its clinical correlation to daily clinical practice.

METHODS

We included 1357 patients with diabetes (56.5% women, 90.4% type 2 diabetes) who were followed up in our diabetes outpatient clinic. Presence of NP was evaluated by performing simultaneous DN4 questionnaires and physical examination. Those who had a DN4 score ≥4 were considered to have NP.

RESULTS

The mean age was 58.2±12.1 years, mean duration was 12.5±7.5; (min-max: 1-45) years, mean HbA1c level was 7.8±1.6% (min-max: 5-16.2%), (61.7±6.0mmol/mol; min-max: 31.1-153.6mmol/mol). Three hundred thirteen patients (23%) were diagnosed with NP using the DN4 tool. Male gender (p=0.01), receiving antihypertensive treatment (p=0.01), presence of retinopathy (p<0.001), cardiovascular disease (CVD) (p=0.01) and previously diagnosed neuropathy (p<0.001) were significantly associated with higher NP scores. Those who had increased DN4 scores were more likely to be on oral hypoglycemic agents (OHA)+insulin combinations (p<0.001), had longer diabetes duration (p<0.001) and higher HbA1c levels (p=0.001). Logistic regression model revealed that diabetes duration (OR: 1.02, 95% CI: 1.00-1.04, p=0.007), elevated HbA1c levels (1.11, 1.02-1.21, 0.015), presence of retinopathy (1.41, 1.20-1.64, <0.001), management with at least one OHA (1.47; 1.12-1.92; 0.004) or any insulin regimen (1.62; 1.16-2.27; 0.005) (compared with diet only-regimens) were significantly associated with NP.

CONCLUSION

Utilization of DN4 questionnaire in daily clinical practice is an effective tool in the identification of pain related with peripheral diabetic polyneuropathy.

Chronic pain in type 2 diabetic patients: a cross-sectional study in primary care setting

BACKGROUND

Although diabetes mellitus (DM) is often associated with painful neuropathic syndromes, a significant number of DM patients suffer from non-neuropathic (nociceptive) pain. Unfortunately, there is insufficient data on the epidemiology of nociceptive pain in DM patients and its effect on their quality of life.

OBJECTIVE

To characterize pain in type 2 DM patients, and assess its effect on their quality of life.

METHODS

The study population included 342 type 2 DM patients, 18 years of age and above (mean age 70.7 ± 9.7), who reported having pain. The study questionnaires included the Brief Pain Inventory (BPI), the S-LANSS scale to assess pain with neuropathic features, life impact, and socio-demographic data.

RESULTS

One hundred and fifty-five DM patients (46.5%) reported having pain of predominantly neuropathic origin. Almost 75% of patients with neuropathic pain were females, compared to 57.8% of patients with nociceptive pain (P = 0.002). More patients with neuropathic pain reported constant daily pain (57.6% vs. 42.4%, P < 0.0001), and worse pain during the night (53.3% vs. 46.7%, P = 0.045). The pain affected daily activities, walking capacity, and mood. Patients with neuropathic pain reported a greater negative effect of pain on their quality of life than those with nociceptive pain (41.0% vs. 15.3%, P < 0.0001).

CONCLUSION

The impact of neuropathic pain in DM patients is much more significant than nociceptive pain and affects their quality of life and daily function to a greater degree.

Maladaptive dendritic spine remodeling contributes to diabetic neuropathic pain

Diabetic neuropathic pain imposes a huge burden on individuals and society, and represents a major public health problem. Despite aggressive efforts, diabetic neuropathic pain is generally refractory to available clinical treatments. A structure-function link between maladaptive dendritic spine plasticity and pain has been demonstrated previously in CNS and PNS injury models of neuropathic pain. Here, we reasoned that if dendritic spine remodeling contributes to diabetic neuropathic pain, then (1) the presence of malformed spines should coincide with the development of pain, and (2) disrupting maladaptive spine structure should reduce chronic pain. To determine whether dendritic spine remodeling contributes to neuropathic pain in streptozotocin (STZ)-induced diabetic rats, we analyzed dendritic spine morphology and electrophysiological and behavioral signs of neuropathic pain. Our results show changes in dendritic spine shape, distribution, and shape on wide-dynamic-range (WDR) neurons within lamina IV-V of the dorsal horn in diabetes. These diabetes-induced changes were accompanied by WDR neuron hyperexcitability and decreased pain thresholds at 4 weeks. Treatment with NSC23766 (N(6)-[2-[[4-(diethylamino)-1-methylbutyl]amino]-6-methyl-4-pyrimidinyl]-2-methyl-4,6-quinolinediamine trihydrochloride), a Rac1-specific inhibitor known to interfere with spine plasticity, decreased the presence of malformed spines in diabetes, attenuated neuronal hyperresponsiveness to peripheral stimuli, reduced spontaneous firing activity from WDR neurons, and improved nociceptive mechanical pain thresholds. At 1 week after STZ injection, animals with hyperglycemia with no evidence of pain had few or no changes in spine morphology. These results demonstrate that diabetes-induced maladaptive dendritic spine remodeling has a mechanistic role in neuropathic pain. Molecular pathways that control spine morphogenesis and plasticity may be promising future targets for treatment.

Prevalence of peripheral neuropathy and painful peripheral neuropathy in Turkish diabetic patients

The aim of this study was to determine the prevalence of diabetic peripheral neuropathy (DPN) and neuropathic pain in diabetic patients attending university outpatient clinics in Turkey. In this multicenter cross-sectional study, neurologic examinations and nerve conduction studies along with clinical diabetic neuropathy score, and Leeds Assessment of Neuropathic Symptoms and Signs pain scale were performed on 1,113 patients (46.2% male) from 14 centers. Prevalence of DPN determined only by clinical examination was 40.4% and increased to 62.2%, by combining nerve conduction studies with clinical examination. According to Leeds Assessment of Neuropathic Symptoms and Signs scores, neuropathic pain prevalence was 16.0% in those who reported pain. Poor glycemic control, retinopathy, microalbuminuria, hyperlipidemia, diabetic foot, and foot amputation were more commonly observed in patients with DPN. Clinical DPN affected 40.4% of diabetic patients, and neuropathic pain prevalence in diabetic patient population was 14.0%. Clinical examinations and nerve conduction studies are important components for early detection and accurate diagnosis of DPN and painful DPN.

Ameliorative potential of spironolactone in diabetes induced hyperalgesia in mice

The present study was designed to investigate the ameliorative potential of spironolactone against diabetic hyperalgesia in mice. Tail flick latency, an index of hyperalgesia, was assessed by analgesiometer. Serum nitrite levels, an index of nitric oxide, were analyzed by Griess reaction. Mice were rendered diabetic with streptozotocin (200 mg kg(-1) i.p) and kept for 30 days for development of diabetic pain. Thereafter, spleen homogenate supernatant (SHS) was prepared from the mouse spleen and administered in normal mice for 14 days. In both diabetic and SHS-treated mice a significant degree of hyperalgesia was developed, suggesting the key role of spleen-derived factor in induction of diabetic pain. Moreover, the levels of nitric oxide were also elevated in 30th day diabetic mice and SHS-treated mice. Administration of spironolactone (7 and 15 mg kg(-1) p.o.) significantly attenuated diabetes-induced decrease of nociceptive threshold and increase of serum nitrite oxide levels. Furthermore, SHS of spironolactone-treated diabetic mice failed to induce hyperalgesia and to increase serum nitrite levels. These results suggest that spironolactone has ameliorative potential in attenuating the hyperalgesia associated with diabetes, which may be possibly mediated through inhibition of release of certain critical factors from spleen.

The effect of venlafaxine HCl on painful peripheral diabetic neuropathy in patients with type 2 diabetes mellitus

OBJECTIVE

The objective of this study was to evaluate the efficacy of venlafaxine HCl in the symptomatic treatment of painful peripheral diabetic neuropathy (PPDN) among patients with type 2 diabetes mellitus (DM).

DESIGN

This study was designed as a prospective, randomized, and controlled trial.

SETTING

This study was conducted at the Dicle University Medical Faculty (Diyarbakir, Turkey).

PATIENTS

Sixty type 2 DM outpatients (47 females and 13 males) with PPDN who had a minimum visual analog scale (VAS) score of 40 mm were enrolled in this study.

INTERVENTIONS

Patients randomized to the treatment group (n=30) received venlafaxine HCl, whereas those randomized to the control group (n=30) received a combination of vitamins B(1)and B(6) tablets.

MEASURES

Severity of pain was measured by VAS, Short-Form McGill Pain Questionnaire, and numerical analog scale scores at admission and at the second, fourth, and eighth weeks of the study. Polyneuropathy was supported by electromyelography.

OUTCOME

In the treatment group, severity of pain was measured as 70.0+/-13.0 in the VAS, as 24.9+/-6.2 in the Short-Form McGill Pain Questionnaire, and as 7.2+/-1.1 in the numerical analog scale. In the control group, it was measured as 73.0+/-8.0 in the VAS, as 26.8+/-6.2 in the Short-Form McGill Pain Questionnaire, and as 7.4+/-0.8 in the numerical analog scale (P>.05).

RESULTS

The most common form of PPDN was distal symmetrical sensorimotor polyneuropathy in both groups (46.8% vs. 50.0%). At the end of the study, there was a significant difference in severity of pain between the groups. In the treatment group, scores were 8.5+/-5.2 and 3.1+/-1.6 in the Short-Form McGill Pain Questionnaire and numerical analog scale, respectively; in the control group, these were 20.5+/-7.0 and 5.5+/-1.6, respectively (P<.001).

CONCLUSIONS

Venlafaxine HCl is a safe and well-tolerable analgesic drug in the symptomatic treatment of PPDN; however, it has minimal adverse effects. It showed its efficacy markedly in the second week of therapy.

Activation of dorsal horn microglia contributes to diabetes-induced tactile allodynia via extracellular signal-regulated protein kinase signaling

Painful neuropathy is one of the most common complications of diabetes, one hallmark of which is tactile allodynia (pain hypersensitivity to innocuous stimulation). The underlying mechanisms of tactile allodynia are, however, poorly understood. Emerging evidence indicates that, following nerve injury, activated microglia in the spinal cord play a crucial role in tactile allodynia. However, it remains unknown whether spinal microglia are activated under diabetic conditions and whether they contribute to diabetes-induced tactile allodynia. In the present study, using streptozotocin (STZ)-induced diabetic rats that displayed tactile allodynia, we found several morphological changes of activated microglia in the dorsal horn. These included increases in Iba1 and OX-42 labeling (markers of microglia), hypertrophic morphology, the thickness and the retraction of processes, and in the number of activated microglia cells. Furthermore, in the dorsal horn of STZ diabetic rats, extracellular signal-regulated protein kinase (ERK) and an upstream kinase, Src-family kinase (SFK), both of which are implicated in microglial functions, were activated exclusively in microglia. Moreover, inhibition of ERK phosphorylation in the dorsal horn by intrathecal administration of U0126, an inhibitor of ERK activation, produced a striking alleviation of existing, long-term tactile allodynia of diabetic rats. We also found that a single administration of U0126 reduced the expression of allodynia. Together, these results suggest that activated dorsal horn microglia may be a crucial component of diabetes-induced tactile allodynia, mediated, in part, by the ERK signaling pathway. Thus, inhibiting microglia activation in the dorsal horn may represent a therapeutic strategy for treating diabetic tactile allodynia.

Assessing the impact of pharmacologic intervention on the quality of life in diabetic peripheral neuropathic pain and fibromyalgia

Chronic, neuropathic pain may be secondary to myriad etiologies including diabetic peripheral neuropathy and fibromyalgia. It is a debilitating condition that imposes a significant burden on individuals and society alike. This article will review various instruments designed to assess quality of life (QoL) and key data assessing QoL of patients suffering from these diseases as well as currently available pharmacologic agents for symptomatic management. As basic and clinical science progress over the next few years, along with the introduction of novel pharmacologic agents, we anticipate greater potential for pain intervention and improvement in the quality of life of our patients.

Altered antinociceptive efficacy of tramadol over time in rats with painful peripheral neuropathy

Pain due to peripheral nerve injury or disease is a dynamic process, such that the mechanism that underlies it alters over time. Tramadol has been reported to be analgesic in clinical neuropathic pain, with varying levels of efficacy due to a patient population that has had neuropathic pain for a wide range of time. In order to address and examine the issue, the antinociceptive efficacy of tramadol over time was tested in rats with a chronic constriction injury (CCI) of the left sciatic nerve. Rats developed a robust hind paw hypersensitivity to innocuous mechanical stimulation ipsilateral to CCI surgery. Subcutaneous injection of tramadol in rats two weeks after CCI surgery dose-dependently attenuated mechanical hypersensitivity, which was abolished with the mu-opioid receptor antagonist naloxone but not the alpha(2)-adrenoceptor antagonist yohimbine. Systemic tramadol also attenuated mechanical hypersensitivity four weeks after CCI surgery, but the efficacy significantly diminished at this time point. In addition, the effect of tramadol at this later time point could be reduced with yohimbine as well as naloxone. These data demonstrate that the efficacy of tramadol depends in part on the duration of nerve injury-evoked nociception, and that its antinociceptive mechanism changes over time. Alteration in antinociceptive mechanism over time may explain the inconsistency in efficacy of this and other analgesic drugs in chronic pain patients.

Development and validity testing of the neuropathy total symptom score-6: questionnaire for the study of sensory symptoms of diabetic peripheral neuropathy

OBJECTIVE

The aim of this study was to develop and validate a neuropathy sensory symptom scale, the Neuropathy Total Symptom Score-6 (NTSS-6), which evaluates individual neuropathy sensory symptoms in patients with diabetes mellitus (DM) and diabetic peripheral neuropathy (DPN) in clinical trials, with the intent of distinguishing a response to therapy.

METHODS

The NTSS-6 questionnaire was developed to evaluate the frequency and intensity of individual neuropathy sensory symptoms identified frequently by patients with DPN (ie, numbness and/or insensitivity; prickling and/or tingling sensation; burning sensation; aching pain and/or tightness; sharp, shooting, lancinating pain; and allodynia and/or hyperalgesia). The NTSS-6 was administered 8 times over a 1-year period to DPN patients. The NTSS-6's reliability (determined by internal consistency and test-retest reproducibility), construct validity, convergent validity, and minimally clinically important differences (MCIDs) were determined.

RESULTS

The NTSS-6 was administered to a total of 205 patients at 10 centers in the United States, Canada, Belgium, Germany, Hungary, Croatia, Slovenia, and the United Kingdom. Internal consistency was demonstrated at all 8 visits (Cronbach's alpha > 0.7). Test-retest reproducibility (intraclass correlation coefficient >0.9) was observed during the baseline period and at end point. Construct validity was demonstrated by statistically significant correlations between the NTSS-6 total score and the Neuropathy Symptoms and Change (NSC) score (r = 0.773-0.885, P < 0.001). Convergent validity was demonstrated by statistically significant correlations between the change in NTSS-6 total scores and the following: change in NSC scores (r = 0.519-0.708, P < 0.001); change in Neuropathy Impairment Score of the Lower Limbs and composite nerve function scores (r = 0.188-0.202, P < 0.007), and categories of the Clinical Global Impressions (r = 0.402, P < 0.001). The within- and between-groups MCIDs for the total NTSS-6 total scores were -1.26 and 0.97 points, respectively. The mean (SD) within-group MCID for all patients who improved on the Clinical Global Impression was -2.29 (3.4) points.

CONCLUSIONS

The NTSS-6 provided a valid assessment of neuropathy sensory symptoms in this sample of patients with DM and DPN, which suggests that it may be useful for symptom evaluation in clinical trials and practice. The NTSS-6 showed internal consistency, test-retest reliability, and construct validity. There was also convergent validity of the scores, indicating that the NTSS-6 may be a suitable questionnaire for clinical trials that evaluate symptoms of DPN in this well-defined patient population.

Diabetic peripheral neuropathic pain: clinical and quality-of-life issues

Diabetic peripheral neuropathy (DPN) is estimated to be present in 50% of people living with diabetes mellitus (DM). Comorbidities of DM, such as macrovascular and microvascular changes, also Interact with DPN and affect its course. In patients with DM, DPN Is the leading cause of foot ulcers, which in turn are a major cause of amputation in the United States. Although most patients with DPN do not have pain, approximately 11% of patients with DPN have chronic, painful symptoms that diminish quality of life, disrupt sleep, and can lead to depression. Despite the number of patients affected by DPN pain, little consensus exists about the pathophysiology, best diagnostic tools, and primary treatment choices. This article reviews the current knowledge about and presents recommendations for diagnostic assessment of DPN pain based on a review of the literature.

Early painful diabetic neuropathy is associated with differential changes in the expression and function of vanilloid receptor 1

Diabetes mellitus is associated with one or more kinds of stimulus-evoked pain including hyperalgesia and allodynia. The mechanisms underlying painful diabetic neuropathy remain poorly understood. Previous studies demonstrate an important role of vanilloid receptor 1 (VR1) in inflammation and injury-induced pain. Here we investigated the function and expression of VR1 in dorsal root ganglion (DRG) neurons isolated from streptozotocin-induced diabetic rats between 4 and 8 weeks after onset of diabetes. DRG neurons from diabetic rats showed significant increases in capsaicin- and proton-activated inward currents. These evoked currents were completely blocked by the capsaicin antagonist capsazepine. Capsaicin-induced desensitization of VR1 was down-regulated, whereas VR1 re-sensitization was up-regulated in DRG neurons from diabetic rats. The protein kinase C (PKC) activator phorbol 12-myristate 13-acetate blunted VR1 desensitization, and this effect was reversible in the presence of the PKC inhibitor bisindolylmaleimide I. Compared with the controls, VR1 protein was decreased in DRG whole-cell homogenates from diabetic rats, but increased levels of VR1 protein were observed on plasma membranes. Of interest, the tetrameric form of VR1 increased significantly in DRGs from diabetic rats. Increased phosphorylation levels of VR1 were also observed in DRG neurons from diabetic rats. Colocalization studies demonstrated that VR1 expression was increased in large myelinated A-fiber DRG neurons, whereas it was decreased in small unmyelinated C-fiber neurons as a result of diabetes. These results suggest that painful diabetic neuropathy is associated with altered cell-specific expression of the VR1 receptor that is coupled to increased function through PKC-mediated phosphorylation, oligomerization, and targeted expression on the cell surface membrane.