The American Diabetes Association (1998) estimates that about 16 million Americans have diabetes. Of these, about one-half are unaware that they have the disease. Diabetic neuropathy is a common secondary complication that is present in over 50 percent of patients but only 13 percent are aware of symptoms. Diagnosis of neuropathy would be facilitated by a more sensitive non- invasive screening test. This would allow earlier onset of tight control of blood glucose, before irreversible changes occur. The distal degenerative characteristic of diabetic neuropathy suggests that the earliest morphological signs of sensory involvement occur in the most distal segment of sensory nerves. These are the epidermal nerve fibers (ENFs) which are class C nociceptors. In some patients there is severe depletion of ENFs, even in the presence of mild thinning of the subepidermal plexus, just 50 mum deeper. We hypothesize that detection of beginning degeneration of ENFs will be the earliest diagnostic morphological sign of diabetic neuropathy and that regeneration of ENFs will be the first sign of reversal of neuropathy. We will attempt to establish new methods for early diagnosis by quantifying ENFs in skin biopsies and skin blisters of asymptomatic patients with diabetes of short duration who have minimal or no neuropathy and in non symptomatic proximal skin areas of patients with known neuropathy. Recently there have been several clinical trials for treatment of diabetic neuropathy. However, the current diagnostic tests do not have the sensitivity required to evaluate patient benefit. We believe that the skin biopsy and skin blister methods can fill this void. We will first determine the ability of diabetic subjects to reinnervate epidermis by studying ENF regeneration in two specific patient groups in which conditions are favorable for regeneration to occur. The first are patients with diabetic neuropathy who will be subjected to a small standardized blister wound that is known to heal and reinnervate rapidly in normal subjects. The second are patients who have a functioning pancreas transplant who are subsequently euglycemic and are therefore no longer diabetic. Lastly, this project will use skin biopsy and skin blister methods to determine if nerve growth factor (NGF) can enhance collateral sprouting and regeneration of epidermal nerve fibers in the above blister wound. Of the neurotrophins entered into clinical therapeutic trials for diabetic neuropathy, NGF may have the most potential to enhance ENF regeneration because of its specificity for dorsal root ganglia neurons which are the cells of origin of ENFs. If NGF can enhance reinnervation in the skin wound these methods may be useful to evaluate the results of clinical therapeutic trials.
| Kennedy, William R (2004) Opportunities afforded by the study of unmyelinated nerves in skin and other organs. Muscle Nerve 29:756-67 |
