The natural history of painful diabetic neuropathy--a 4-year study

Clinical observations and experiments in diabetic neuropathy

Diabetic neuropathies form a group of diverse conditions, which can be distinguished between those which recover (acute painful neuropathies, radiculopathies, mononeuropathies) and those which progress (sensory and autonomic neuropathies). These two main groups can be distinguished in several ways: sensory and autonomic neuropathies are classic diabetic complications progressing gradually in patients with long-standing diabetes who often have other specific complications, while the reversible neuropathies do not have these features. The latter are characterised by their occurrence at any stage of diabetes, often at diagnosis, they may be precipitated on starting insulin treatment, and they are more common in men; they can occur at any age, though more often in older patients, and are unrelated to other diabetic complications. The two groups of neuropathies also show differences in nerve structural abnormalities and with regard to distinctive blood flow responses. The underlying mechanisms responsible for these very different forms of neuropathy remain speculative, but evidence for an immunological basis for the development of severe symptomatic autonomic neuropathy is presented.

Follow-up study of sensory-motor polyneuropathy in type 1 (insulin-dependent) diabetic subjects after simultaneous pancreas and kidney transplantation and after graft rejection

The influence of successful simultaneous pancreas and kidney transplantation on peripheral polyneuropathy was investigated in 53 patients for a mean observation period of 40.3 months. Seventeen patients were followed-up for more than 3 years. Symptoms and signs were assessed every 6 months using a standard questionnaire, neurological examination and measurement of sensory and motor nerve conduction velocities. While symptoms of polyneuropathy improved (pain, paraesthesia, cramps, restless-legs) and nerve conduction velocity increased, there was no change of clinical signs (sensation, muscle-force, tendon-reflexes). Following kidney-graft-rejection there was a slight decrease of nerve conduction velocity during the first year, which was not statistically significant. Following pancreas-graft rejection there was no change of nerve conduction velocity during the first year. Comparing the maximum nerve conduction velocity of the patients with pancreas-graft-rejection to the nerve conduction velocities of these patients at the end of the study, there was a statistically significant decrease of 6.5 m/s. In conclusion, we believe that strict normalization of glucose metabolism alters the progressive course of diabetic polyneuropathy. It may be stabilized or partly reversed after successful grafting even in long-term diabetic patients.

Clinical presentation and management of diabetic neuropathy and foot ulceration

A simple classification of the more common neuropathies is presented. The most frequent disorder in diabetes is a symmetrical sensory polyneuropathy in the lower limbs. Acute sensory polyneuropathies frequently follow sudden metabolic disturbance although there may be little evidence of neurological abnormalities on clinical examination. Similar symptoms occur with chronic sensory polyneuropathy but onset is gradual and this condition may persist for years with only minor symptoms. A significant proportion of patients with chronic polyneuropathies have few if any symptoms and are only diagnosed by careful clinical examination. An approach to the diagnosis and management of symptomatic sensory polyneuropathy is suggested. Sensory loss, and the possible complication of vascular dysfunction, greatly increases the risk of insensitive foot lesions in diabetic patients. Some may progress to the insensitive foot without prior evidence of neuropathy. Regular and thorough examination is therefore the only way to identify patients at risk who then require education in preventative foot care. The identification of such patients and the clinical presentation and management of foot ulcers is discussed.

A multicentre trial of the aldose-reductase inhibitor, tolrestat, in patients with symptomatic diabetic neuropathy

The effects of the aldose-reductase inhibitor, tolrestat, on chronic symptomatic diabetic sensorimotor neuropathy were studied during a placebo-controlled, randomised, 52-week multicentre trial. Of the four tolrestat doses investigated, only the highest dose group, 200 mg once daily, showed subjective and objective benefit over baseline and placebo, and further analyses are confined to this group (n = 112) and placebo (n = 107). Painful and paraesthetic symptoms were analysed separately: improvement in paraesthetic symptoms were seen at one year (p = 0.04), though painful symptoms improved on both placebo and active therapies. Significant improvement in both tibial and peroneal motor nerve conduction velocities were seen at 52 weeks. Tolrestat 200 mg once daily was significantly better than placebo in producing concordant improvements in both motor nerve conduction velocities and paraesthetic symptom scores at 24 weeks (p = 0.01), 42 weeks (p = 0.01) and 52 weeks (p = 0.02). Long-term benefit [concordant improvement at 24 weeks maintained until 52 weeks] was seen in 28% of treated patients compared to 5% on placebo (p = 0.001). It is concluded that some sustained improvement in symptomatic diabetic neuropathy may be obtained following aldose-reductase inhibition with tolrestat 200 mg once daily.

Early increase in CGRP- and VIP-immunoreactive nerves in the skin of streptozotocin-induced diabetic rats

We have previously shown depletion of nerves and neuropeptides in skin biopsies of diabetic patients, even in the absence of clinical signs and symptoms of sensory and autonomic neuropathy, but were unable to examine the changes occurring at an early stage of the disease. Therefore, the distribution and relative density of peptide-containing nerves was studied in streptozotocin-treated rats in order to assess the progression of neural changes in the initial stages of diabetes. Skin samples dissected from the lip and footpad of diabetic rats, 2, 4, 8 and 12 weeks after streptozotocin injection and age matched controls were sectioned and were immunostained with antisera to the neuropeptides substance P, calcitonin gene-related peptide (CGRP), vasoactive intestinal polypeptide (VIP) and neuropeptide Y (NPY), and to a general neural marker, protein gene product 9.5 (PGP 9.5). No change was apparent in the distribution or relative density of immunoreactive cutaneous nerve fibres 2, 4 and 8 weeks after streptozotocin treatment. By 12 weeks there was a marked increase in the number of CGRP-immunoreactive fibres present in epidermis and dermis, and of VIP-immunoreactive fibres around sweat glands and blood vessels. A parallel increase was seen in nerves displaying PGP 9.5 immunoreactivity. No differences were detected in nerves immunoreactive for either substance P in the epidermis and dermis, and NPY around blood vessels. The alterations in the peptide immunoreactivities may be similar in the initial stages of human diabetes.

Diabetic neuropathies and pain

Many of the diabetic neuropathic syndromes are characterized by painful symptoms with a sensation of burning and associated with troublesome hyperaesthesia. It is important to distinguish between the acute and chronic forms of peripheral sensory neuropathy; while the former carries an excellent prognosis for symptomatic improvement within one year, the latter may cause persistent symptoms for many years. In contrast to the acute form, in which symptoms are particularly severe but abnormal neurological signs are minimal, patchy stocking and glove sensory loss together with peripheral small muscle wasting are often present in chronic sensorimotor neuropathy. Peripheral polyneuropathies are more common in patients with poor metabolic control, although recent evidence implicates blood glucose flux as a possible contributory factor to neuropathic pain. It is possible that blood glucose flux or altered peripheral blood flow leads to increased spontaneous activity in nociceptive afferent fibres which are present in the axonal sprouts that characterize small fibre neuropathy. In the diagnosis of the neuropathies, exclusion of other aetiological factors is of paramount importance as there is no specific diagnostic test for diabetic nerve damage. If there is no symptomatic improvement after a period of stable and optimal metabolic control together with simple analgesics, then the tricyclic drugs should be regarded as first line therapy. The rapid effect of these drugs suggests a peripheral rather than central mode of action.

The distribution of diabetic neuropathy in a British clinic population

A survey of over 1,000 diabetic patients attending a routine hospital clinic clinic in a British city revealed 104 with neuropathic symptoms or foot ulceration. Patients could be assigned to one of four clinical neuropathy groups: chronic sensorimotor, predominantly sensory, proximal motor and mononeuropathy. Only duration of diabetes differed significantly between the groups, with the longest duration in the chronic sensorimotor group. Objective measures of neuropathy did not correlate with symptom scores indicating that careful clinical assessment must augment neurophysiological studies. Patients with neuropathic foot ulceration had significantly higher vibration and thermal thresholds compared with neuropathic patients without ulceration, whereas there was no difference in autonomic function between the two groups.

Diabetic neuropathies. Current concepts in prevention and treatment

Diabetic nerve damage leads to a wide variety of unpleasant problems: painful sensations, muscle weakness, numb feet predisposing to ulcers, impotence, and a series of distressing effects due to autonomic dysfunction. At present, there is no single effective treatment for the many clinical syndromes--each of which may well have a different cause. Improved blood glucose control must remain the first line of treatment, hopefully to improve nerve structure and function but also to raise the pain threshold. A variety of sedatives and analgesics may also help some patients. Inhibition of the enzyme aldose reductase with resultant interference with neural sorbitol and myo-inositol metabolism would seem to have a good theoretical basis in therapy, and detailed results of long term clinical trials of aldose reductase inhibitors such as sorbinil and tolrestat are awaited with interest. Their role in the future could be more important in prevention of nerve damage than in attempting to reverse gross end-stage nerve destruction. In diabetic subjects with loss of pain sensation in the foot due to neuropathy or in the more advanced state of foot ulceration, intensive educational and clinical efforts should be exerted to prevent this distressing and common problem. In the future, a more detailed understanding of the biochemical abnormalities occurring in nerves and their effect on nerve function, structure and vasculature may lead to more satisfactory and logical treatments for this the commonest single complication of diabetes.

Pain relief in diabetic neuropathy: the effectiveness of imipramine and related drugs

Experience of treating 80 consecutive patients with painful diabetic neuropathy and a double-blind study of imipramine in acute painful neuropathy are reported. A standard stepwise protocol was used, based on imipramine as the drug of first choice, substitution of amitriptyline or mianserin as second choice, and, thirdly, addition of phenothiazine or clonazepam if necessary. Sixty per cent were satisfied with imipramine alone and all but 3 (5%) were improved by the stepwise scheme. Paradoxically, the most effective analgesia was obtained in those with the most severe and unpleasant pain. Often 150 mg of imipramine or amitriptyline was necessary. The onset of analgesia and relapse after withdrawal of treatment were rapid, facilitating clinical use, and suggesting a peripheral rather than central drug action.

Breaking the Cycle of Pain In Diabetic Peripheral Neuropathy

An attitude of helplessness pervades both patients and health professionals when dealing with the problems of dia betic peripheral neuropathy. Those afflicted are often over whelmed by the pain and find themselves unable to fulfill the daily requirements of their diabetes regimen. The in consistencies in amounts and timing of meals, levels of ac tivity, and scheduling of insulin injections can result in hyperglycemia, a state that has been found to correlate strongly with the occurrence of nerve damage. Thus the pain perpetrates itself. For the health professional, having to confront this devastating pain without objective factors to assess and few scientific treatment measures to offer con tributes to a sense of inadequacy and ignorance. It is fre quently assumed that "nothing can be done." In reality, health professionals do have something to offer the person suffering from this condition. First, they can provide infor mation about the relationship between control and compli cations, and explain the need for the patient to change those behaviors that may be perpetuating the pain. Sec ond, and most importantly, health professionals can con vey support and confidence, without which many patients will be unable to make the changes in their behavior neces sary to resolve their pain.