Detecting And Treating Patients With Diabetic Autonomic Neuropathy

Author(s): 
By Damieon Brown, DPM and Javier La Fontaine, DPM
Nerve function involves large nerve fibers and small nerve fibers. Tests such as vibration, proprioception and loss of protective sensation, deep tendon reflexes, muscle strength, two-point discrimination and pinprick are good indicators of large fiber neuropathy.2 These patients present with symptoms such as lacinating pain, radiating pain, heaviness or numbness in the feet and legs. Clinically, one may note wasting of the intrinsic muscle of the foot with cheiroarthropathy or ankle equinus. Nerve conduction velocity is rarely indicated for diagnosing diabetic neuropathy and is primarily a large fiber test. Small fiber nerve functions account for perception of heat, cold and pain sensation. Signs and symptoms of small fiber neuropathy include burning, cold feet, a feeling of being on “pins and needles” and hyperalgesia. Unfortunately, a practical diagnostic test for small fiber neuropathy does not exist yet. Several tests are described in the literature. The quantitative sudomotor axon reflex test (QSART) machine enables one to measure the sweating function of the foot. However, the variability of the test is not well understood. Although autonomic neuropathy is considered a small fiber neuropathy, it is imperative to identify these patients with autonomic neuropathy by questioning specific signs and symptoms that they may experience. Asking the patient about symptoms such as gastroparesis, incontinence, sexual dysfunction and dizziness with change in position (postural hypotension) may help facilitate an appropriate and timely diagnosis. How Autonomic Neuropathy Can Adversely Affect Wound Healing Hyperglycemia is the most important risk factor when it comes to the pathogenesis of diabetic microvascular disease or “functional microcirculation.” Although it is not well understood, changes in hydrostatic pressure at the level of capillaries will lead to increased permeability of plasma proteins leading to endothelial dysfunction and loss of autoregulation. One of the theories that may explain the effect of functional microcirculation in wound healing is the loss of control of the arteriovenous shunting caused by autonomic neuropathy (small fiber neuropathy), specifically the c-fibers. This process will lead to oxygenation of the venous blood and shunting of blood away from the skin, which leads to tissue hypoxia. Case Study: Trying To Heal A Stubborn Puncture Wound A 56-year-old Hispanic female presented to our institution three weeks after experiencing a puncture wound to her left hallux. She noted a throbbing pain and increased swelling in this area two days prior to her visit. The patient did not seek professional help until her emergency room visit. Her past medical history includes NIDDM for eight years, hypertension, hyperlipidemia, coronary artery disease, myocardial infarction in 1995, nephropathy and retinopathy. Her current medications include metformin, glipizide, enalapril and Toprol XL. She had smoked for 40 years but quit in 1995. She denied any alcohol consumption. Upon a physical examination, we found that the obese patient had a palpable dorsalis pedis pulse but a barely palpable posterior tibial pulse in both feet. Her capillary filling time was less than three seconds. She also demonstrated a loss of protective sensation to 10 sites in both feet. We noted dry, xerotic skin in the lower extremities and no pedal hair. Her puncture wound was on the plantar aspect of her left hallux with erythema extending through the first interspace and a full thickness dry eschar in the lateral aspect of the hallux. A laboratory evaluation was within normal limits. Radiographs revealed no foreign body nor signs of osteomyelitis. Since there were concerns about her blood flow status, we ordered non-invasive studies. Significant findings included a left ABI of .91, a TBI of .43 and biphasic waveforms to the anterior tibial artery and posterior tibial artery. Transcutaneous oximetry at the midfoot level demonstrated a response from 1 to 23 mmHg to 100 percent oxygen challenge for 10 minutes. Vascular surgery recommended that the patient should heal. We first performed an open partial first ray amputation, which demonstrated a local abscess at the first interspace with a significant soft tissue loss. However, five days after the surgery, the wound did not progress. After again consulting the vascular team, we performed an angiogram.

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