When Patients With Diabetes Have Lower Extremity Nerve Entrapments

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By Greg Mowen, DPM

Editor’s note: Peripheral nerve decompression for patients with diabetes and lower extremity neuropathy continues to be a hotly debated topic in podiatric medicine and other specialties. The driving force of evidence based medicine has looked critically upon this procedure while many respected surgeons in a variety of fields have found great clinical successes. Dr. Mowen reviews many of the debate topics and presents some helpful information and opinion in this column. — Dr. Steinberg    It has long been recognized that patients with diabetes experience a higher rate of carpal tunnel syndrome (CTS) than those without diabetes.1,2 Anecdotally, most family doctors, endocrinologists and neurologists seem to agree that upper extremity entrapments are very common among patients with diabetes.    In my clinical experience, many of those same physicians do not recognize that patients with diabetes have a higher rate of lower extremity entrapments like tarsal tunnel syndrome. Lower extremity nerve pain and neuropathic symptoms are often too readily diagnosed as peripheral neuropathy and practitioners do not look for treatable entrapments.    It is theorized that sorbitol will build up in the peripheral nerves, causing an increase in the osmolar properties and subsequently swelled nerves. Nerves will then become entrapped in tight anatomical areas such as the carpal tunnel. Entrapments will cause a decrease in axoplasmic flow and a decrease in the microcirculation of the nerve.3    Accordingly, it seems sensible that this same process is also occurring in the lower extremity, perhaps even to a much greater degree due to the mechanical stress in the legs and feet. Often, the lower extremity has poorer circulation compared to the upper extremity. High-resolution ultrasound has shown the posterior tibial nerve to have a greater diameter in diabetic peripheral neuropathy (DPN) in comparison to patients without diabetes.4    With swollen nerves, it seems only logical there will be more pressure on the nerves in tight anatomical locations. The tibial nerve and its branches are compressed in the tarsal tunnel and within the porta pedis. The common peroneal gets trapped at the fibular head under the fascia of peroneus longus and the deep peroneal nerve on the dorsum of the foot under the extensor digitorum brevis tendon. These multiple sites cause the “multiple crush” phenomenon and can lead to a symmetric polyneuropathy. The theory of triple or multiple compression has been the basis of triple decompression surgery to treat DPN.

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