Current And Emerging Tools For Assessing Diabetic Peripheral Neuropathy

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Author(s): 
Maria K. Piemontese, DPM, and Andrew J. Meyr, DPM

   Sensorimotor neuropathy is a combination pathologic process with symptoms ranging from pain, numbness and paresthesia to decreased strength and atrophy of lower limb muscles. This form of neuropathy typically affects the smaller intrinsic muscles first. One can readily appreciate how atrophy of the intrinsics can lead to muscular imbalance, particularly about the digits at the metatarsophalangeal joint (MPJ) level, and subsequent deformity. This motor neuropathy can lead directly to foot deformity, which is a part of the aforementioned critical triad.

   An additional form of motor neuropathy, diabetic amyotrophy, affects the proximal lower extremities and can lead to additional muscle atrophy and weakness. This may clinically manifest itself as subjective complaints of difficulty walking, sensations of instability and a history of falls.13 In fact, these patients can have up to 15 times the risk for injury when walking in comparison to those without diabetic motor neuropathy.14 Additionally, research has suggested that Charcot neuroarthropathy may be influenced by diabetic motor neuropathy. Jeffcoate and colleagues have proposed that motor neuropathy results in joint instability and subluxation with altered force distribution throughout the foot.15

   The motor portion of neuropathy clearly comes with its own set of associated risks and potential outcomes if it is undetected and undertreated. Some treatment options may include muscle strengthening and gait training through physical therapy, orthotics and bracing when indicated. It is important to note that pharmacologic agents such as pregabalin (Lyrica, Pfizer) or tricyclic antidepressants are antinociceptive in nature, and are unlikely to play a significant role in motor neuropathy management.16

   Autonomic neuropathy primarily involves the cardiovascular system, gastrointestinal system and the genitourinary system, but it can have effects on the lower extremity as well in the form of an altered and at-risk cutaneous system. Sweat gland dysfunction may lead to dry, cracked skin while microvascular shunting produces negative effects on capillary blood flow in the setting of this type of neuropathy.

   Gibbons and co-workers sought to evaluate the density of nerve fibers innervating sweat glands in healthy controls and patients with diabetes.17 The authors conducted skin biopsies at three sites (proximal thigh, distal thigh and distal leg) and examined the nerve fibers innervating sweat glands. They found that patients with diabetes had reduced sweat gland nerve fiber density, which was associated with a worsening severity of neuropathy.

   Autonomic dysfunction presents with significant lower extremity and systemic effects. Edmonds and co-workers studied an interesting facet of autonomic neuropathy in three groups of patients.18 They found that heart rate during deep breathing and stance was significantly slower in diabetic patients with foot ulceration in comparison to normal controls and diabetic patients without a history of foot ulceration. The authors concluded that severely abnormal autonomic function occurs in association with neuropathic foot ulceration but patients without ulcers have lesser degrees of autonomic neuropathy.

   Another condition to be aware of is known as “hypoglycemic unawareness.” During this, a patient does not experience the normal symptoms of hypoglycemia (sweating, rapid heartbeat) that act as a warning system.

What Are The Best Methods Of Detecting Neuropathy?

It is well accepted that peripheral neuropathy is a risk factor for developing foot ulceration and that early detection leading to adequate foot care can reduce amputation rates by about 50 to 80 percent.19 This emphasizes the need for assessment tools that are simple, objective, reproducible and comprehensive. How well are we doing in this respect?

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