Detecting And Treating Patients With Diabetic Autonomic Neuropathy
How Does This Relate To The Diabetic Foot?
The autonomic nervous system controls microvascular skin flow.3 In the diabetic population, the rhythmic contraction of small vessels such as arterioles, venules and small arteries is affected. Loss of control of these vessels will increase blood flow in the absence of large vessel peripheral arterial occlusive disease. This is also a consequence of increased arteriovenous shunting and results in a warm foot with distended dorsal foot veins.4 According to Low, et. al., this physiological problem may lead to diabetic neuropathy as well.5
This problem resembles premature aging. The clinical pedal manifestations of autonomic neuropathy are dry skin, loss of sweating, distended veins and fissuring, which may lead to ulcerations, infection and gangrene.6 It has been documented in the literature that autonomic neuropathy may increase osteoclastic activity, resulting in reduced bone density. Young, et. al., found reduced bone density in the lower limbs of 17 patients with Charcot in comparison to 10 neuropathic control subjects.7 Therefore, Charcot arthropathy may reflect the severity of autonomic neuropathy.
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.