Painful symptoms and foot ulceration are the two most important clinical problems related to peripheral somatic diabetic neuropathy. The conduction of clinical trials, which test the efficacy of new therapies for painful neuropathy is straight forward:
From: Contemporary Diabetes: Diabetic Neuropathy: Clinical Management, Second Edition Edited by: A. Veves and R. Malik © Humana Press Inc., Totowa, NJ
patients with this condition are provided trial medication and the primary end point is the reduction of the symptoms, which is expected to occur during a reasonable period after the treatment has been initiated. In contrast, foot ulcers develop long after the initiation of events which lead to nerve damage and, by this time, the possibility of restoring the nerve lesions, or halting their progression, is close to nonexisting. Therefore, if a study was to be conducted having as primary end point the prevention of foot ulceration it should involve patients who have diabetic neuropathy in the early stages and follow them until they reach the very late stages of the disease. This would mean that a large number of patients should be followed for prolonged periods of time, even decades, before any conclusion would be reached.
It is obvious from the aforementioned that more practical end points should be used in order to conduct clinical therapeutic trials, which will be financially supported by the pharmaceutical industry where efficient development of new medications are of paramount importance. In addition, these end points should give an accurate and more detailed picture about the effects of the treatment on the progression of the disease, mainly to what extent it can restore the already established lesions.
Sural nerve biopsies were initially considered to be the best method for evaluating new medications. However, the interpretation of the biopsy results was found to be more difficult than was originally believed and as a result, nerve biopsies fall out of favor. Most recent studies have used surrogate measurements, mainly nerve electrophysiological measurements and quantitative sensory testing. Regarding the electrophysiological measurements, Dyck and O'Brian, based on epidemiological data, initially suggested that a mean change of 2.9 m per second in the combined conduction velocities of the ulnar, median, and peroneal nerves, or a change of 2.2 m per second in the peroneal nerve alone should be achieved in order that the results can have a meaningful clinical significance (4). However, it should be emphasized that the selection of end points is not the only issue with the design of new clinical trials. Thus, the current prevailing opinion is that future studies will have to include large number of patients and be of long enough duration (probably around 18-24 months), pay particular attention to the variability of the end point measurements, and have rigorous quality control in order to allow the drawing of definite conclusions regarding the efficacy of ARIs in treating diabetic neuropathy.
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