Characterization of Mechanical Allodynia and Skin Innervation in a Mouse Model of Type-2 Diabetes Induced by Cafeteria-Style Diet and Low-Doses of Streptozotocin

Background: Painful distal symmetrical polyneuropathy (DPN) is a frequent complication of type-2 diabetes mellitus (T2DM) that commonly presents as neuropathic pain and loss of skin nerve fibers. However, there are limited therapies to effectively treat DPN and many of the current animal models of T2DM-induced DPN do not appear to mirror the human disease. Thus, we validated a DPN mouse model induced by a cafeteria-style diet plus low-doses of streptozotocin (STZ).

Methods: Female C57BL/6J mice were fed either standard (STD) diet or obesogenic cafeteria (CAF) diet for 32 weeks, starting at 8 weeks old. Eight weeks after starting diets, CAF or STD mice received either four low-doses of STZ or vehicle. Changes in body weight, blood glucose and insulin levels, as well as oral glucose- and insulin-tolerance tests (OGTT and ITT) were determined. The development of mechanical hypersensitivity of the hindpaws was determined using von Frey filaments. Moreover, the effect of the most common neuropathic pain drugs was evaluated on T2DM-induced mechanical allodynia. Finally, the density of PGP -9.5⁺ (a pan-neuronal marker) axons in the epidermis from the hindpaw glabrous skin was quantified.

Results: At 22–24 weeks after STZ injections, CAF + STZ mice had significantly higher glucose and insulin levels compared to CAF + VEH, STD + STZ, and STD + VEH mice, and developed glucose tolerance and insulin resistance. Skin mechanical sensitivity was detected as early as 12 weeks post-STZ injections and it was significantly attenuated by intraperitoneal acute treatment with amitriptyline, gabapentin, tramadol, duloxetine, or carbamazepine but not by diclofenac. The density of PGP-9.5⁺ nerve fibers was reduced in CAF + STZ mice compared to other groups.

Conclusion: This reverse translational study provides a painful DPN mouse model which may help in developing a better understanding of the factors that generate and maintain neuropathic pain and denervation of skin under T2DM and to identify mechanism-based new treatments.

[Diabetes complications - diabetes and the nervous system]

Diabetes mellitus is a chronic metabolic disease associated with multiple long-term complications. Besides macro- and microvascular complications, patient's well-being can be severely impaired by complications affecting the nervous system. About 50 % of patients with diabetes suffer from polyneuropathy. Moreover, the risk of developing cognitive impairment and dementia is also increased in older people with diabetes. Insufficient glycemic control, young age at diagnosis of diabetes are discussed as risk factors for developing diabetes complications. The early identification and prevention of factors predicting diabetes complications that affect the nervous system are still challenging and in need for further research.

Review: The clinical evaluation of lower limb perfusion in diabetic foot disease

Athorough clinical assessment and evaluation of foot perfusion is essential in managing diabetic foot disease. The treatment of macrovascular disease is key to reducing the high amputation rates seen in diabetic patients, particularly as small vessel dysfunction may make diabetic individuals more vulnerable to the effects of macrovascular, atherosclerotic disease. The clinical assessment remains paramount in the management of diabetic foot disease. The confounding effects of peripheral neuropathy on the symptoms and signs of lower limb arterial insufficiency can make assessment difficult. This article provides a resume of the clinical manifestation of lower limb ischaemia and neuropathy and the importance of accurate evaluation of the diabetic foot.

Painful ophthalmoplegia with normal cranial imaging

Background

Painful ophthalmoplegia with normal cranial imaging is rare and confined to limited etiologies. In this study, we aimed to elucidate these causes by evaluating clinical presentations and treatment responses.

Methods

Cases of painful ophthalmoplegia with normal cranial MRI at a single center between January 2001 and June 2011 were retrospectively reviewed. Diagnoses of painful ophthalmoplegia were made according to the recommendations of the International Headache Society.

Results

Of the 58 painful ophthalmoplegia cases (53 patients), 26 (44.8%) were diagnosed as ocular diabetic neuropathy, 27 (46.6%) as benign Tolosa-Hunt syndrome (THS), and 5 (8.6%) as ophthalmoplegic migraine (OM). Patients with ocular diabetic neuropathy were significantly older (62.8 ± 7.8 years) than those with benign THS (56.3 ±12.0 years) or OM (45.8 ± 23.0 years) (p < 0.05). Cranial nerve involvement was similar among groups. Pupil sparing was dominant in each group. Patients with benign THS and OM responded exquisitely to glucocorticoid treatment with resolved diplopia, whereas patients with ocular diabetic neuropathy didn’t (p < 0.05). Patients with OM recovered more rapidly than the other groups did (p < 0.05). Overall, most patients (94.8%) recovered completely during the follow-up period.

Conclusions

Ocular diabetic neuropathy and benign THS accounted for most of the painful ophthalmoplegias in patients with normal cranial imaging. Patient outcomes were generally good.

Recent advances in the pharmacological management of painful diabetic neuropathy

Painful diabetic peripheral neuropathy (DPN) affects 10—26% of all diabetic patients and continues to pose significant clinical/treatment challenges. Pharmacological treatment of painful DPN includes tricyclic antidepressants (TCAs), selective serotonin noradrenaline reuptake inhibitors (SNRIs), selective serotonin reuptake inhibitors, anticonvulsants, opiates, the antioxidant alpha lipoic acid, membrane stabilisers, topical capsaicin etc. Over the past five years many compounds have undergone clinical trials and new agents have immerged. Current first-line therapies for painful DPN are a TCA, SNRI (such as duloxetine) or anticonvulsants (such as pregabalin or gabapentin), taking into account patient co-morbidities and cost. On the basis of cost NICE has recently recommended the use of TCAs before the other first-line agents of painful DPN. Second-line therapies include opiates such as tramadol, morphine and oxycodone.

Advances in the management of diabetic peripheral neuropathy

PURPOSE OF REVIEW

Over the past 5 years there have been significant advances in the pathogenesis and management of diabetic peripheral neuropathic pain (DPNP) and this review attempts to summarize these.

RECENT FINDINGS

Recent research has shown that in addition to poor glucose control, traditional cardiovascular risk factors for macrovascular disease, are independent-risk factors for incident diabetic peripheral neuropathy (DPN). In contrast, the risk factors for DPNP are not known although data from the EURODIAB cohort suggest that female sex may be an independent-risk factor. The pathogenisis of pain in DPNP is also not clear although differences in sural nerve epineurial blood flow, foot skin microcirculation and intraepidermal nerve fibre density (IENF), and thalamic magnetic resonance spectroscopy have been demonstrated between individuals with DPNP and painless neuropathy.Pharmacological treatment of DPNP includes tricyclic compounds (TCAs), selective serotonin noradrenaline reuptake inhibitors (SNRIs), anticonvulsants, opiates, membrane stabilizers, the antioxidant alpha lipoic acid, capsaicin etc. Current first-line therapies for DPNP are a TCA, SNRI (such as duloxetine) or anticonvulsants (such as pregabalin or gabapentin), taking into account patient comorbidities and cost.

SUMMARY

There has recently been a consensus document suggesting an evidence-based protocol for the management of DPNP and this report is highlighted.

New perspectives on the management of diabetic peripheral neuropathic pain

Peripheral neuropathy affects about 30% of people with diabetes mellitus. Between 16% and 26% of diabetes patients experience chronic pain. This may be referred to as diabetic neuropathic pain (DNP) or diabetic peripheral neuropathic pain (DPNP). Minimum requirements for diagnosis of DPNP should include assessment of pain and symptoms and neurological examination, with the accent on sensory examination. Given that depression and other co-morbidities are commonly associated with this condition, a broad approach to management is essential. Lifestyle intervention and optimisation of glycaemic control are recommended as initial steps in management. An evidence-based treatment algorithm for DPNP has been proposed, recommending initial use of either a tricyclic antidepressant, selective serotonin noradrenaline re-uptake inhibitor or alpha-2-delta agonist, depending on patient co-morbidities and contra-indications. Addition of an opioid agonist may be required in the event of inadequate pain control. Irrespective of which treatment is offered, only about one third of patients are likely to achieve more than 50% pain relief. Further research to improve the diagnosis and management of DPNP is needed.