Screening and Diagnosis of Diabetic Neuropathy

Overview of diabetic neuropathy

About half of all people with diabetes have some degree of diabetic neuropathy, which can present as either a polyneuropathy or a mononeuropathy.[1,2,3] Diabetic neuropathy is a common and troublesome complication of diabetes, leading to substantial morbidity and mortality resulting in an annual US cost in 2001 of $13.7 billion.[4,5] Diabetic neuropathy is the most common form of neuropathy in developed countries and is responsible for 50% to 75% of nontraumatic lower-limb amputations.[4] From 2002, about 82,000 nontraumatic lower-limb amputations were performed each year among people with diabetes.[6]

The term “diabetic neuropathy” encompasses many different manifestations of disease, which may be classified and staged as described in Table 1. Diabetic neuropathy is a vast topic, and discussion of each manifestation is outside the scope of this article. The main focus of this article is to summarize the screening and diagnostic procedures for distal symmetric polyneuropathy, often referred to as diabetic peripheral neuropathy (DPN), and to emphasize the importance of early diagnosis.

Table 1. Classification and staging of diabetic neuropathy[4]

Screening for DPN

Therapeutic intervention and prevention of progression of DPN have the greatest impact if instituted very early in the course of disease. Therefore, it is recommended that all patients with diabetes receive routine risk assessment (screening) for DPN at diagnosis and thereafter so that appropriate treatments can be instituted as early as possible. Table 2 outlines the current American Diabetes Association (ADA) recommendations on risk assessment for DPN, and Table 3 describes the characteristics of a foot at high risk for developing ulcers and/or amputations.

The presence of DPN itself may be considered a risk factor for the presence of other diabetic microvascular complications, as there is a strong association between diabetic retinopathy, symmetric peripheral neuropathy, and nephropathy.[1]

The ADA recommends that all patients with diabetes should be screened at least annually for chronic sensorimotor DPN. [7] Screening should begin immediately after a diagnosis of type 2 diabetes and 5 years after the diagnosis of type 1 diabetes.[7] Routine screening for DPN can be achieved through a comprehensive foot exam, ankle reflexes, tuning fork vibration detection, and monofilament screening test. The ADA recommends the monofilament screening test and the tuning fork as screening methods to identify and test for the foot at risk.[9]

A recent analysis compared the various modalities for testing foot ulcer susceptibility a found that the 10 g monofilament may not be the optimum methodology for identifying individuals at risk of foot ulcers.[8] Modalities tested included the 10 g monofilament at four sites on each foot, the 128 Hz tuning fork at the halluces, the Biothesiometer at the halluces and the modified neuropathy disability score. The 128 Hz tuning fork tested at only two sites was as sensitive as the 10 g monofilament tested at eight sites. In addition, the Biothesiometer and the modified neuropathy disability score tend to be more sensitive than the 10 g monofilament for the assessment of individuals at risk for foot ulcers.[8] An overview regarding the use of the monofilament and tuning fork is outlined in Table 4.

In addition to testing, a history of neuropathic symptoms should be elicited, and the feet should be examined for ulcers, calluses, and deformities. The ADA also recommends that all patients with symptomatic or asymptomatic DPN should receive foot care education and potentially should be referred to a podiatrist.[7]

Table 2. ADA risk assessment recommendations for DPN[9]

Table 3. Risk factors for ulcerations and amputations [10]

Table 4. Monofilament and tuning fork overview

Screening schedule recommendations by the ADA are listed in Table 5.

Table 5. ADA screening schedule for DPN[9]

^*People with one or more high risk factors should be evaluated more frequently for development of additional risk factors.

†Pregnancy can exacerbate peripheral neuropathy, especially compartment syndromes (carpal tunnel syndrome).[12]

Diagnosis of DPN

Diabetic neuropathy is a set of clinical syndromes that may be silent and go undetected, while causing damage, or may be present with clinical signs that are nonspecific and insidious. One study indicated that approximately 20% of patients diagnosed with diabetic polyneuropathy actually had neuropathies of nondiabetic etiology.[13] It is important to correctly distinguish nondiabetic neuropathy from diabetic neuropathy, and to differentiate among the different diabetic neuropathies, because they require different therapeutic approaches.[7] Therefore, the diagnosis of DPN is made through exclusion of all other causes.[4] Symptoms of DPN are reported only in approximately 25% of patients with diabetes; 75% show no symptoms at any given point in therapy.[4] However, all patients suffering from DPN experience one or more clinical signs of the disorder, including reduced vibratory sensation, reduced pressure sensation, reduced reflexes, and foot ulcers. Signs and symptoms associated with DPN are shown in Table 6.

Table 6. Signs and symptoms of DPN

Signs	Symptoms
Diminished vibratory perception	Numbness or loss of feeling (asleep or “bunched up sock under toes”sensation)
Decreased knee and ankle reflexes	Prickling/tingling
Reduced protective sensation such as pressure, hot and cold, pain	Aching pain
Diminished ability to sense position of toes and feet	Burning pain, lancinating pain
	Unusual sensitivity or tenderness when feet are touched (allodynia)

A number of routine screening and diagnostic tests are available to enable physicians to assess the incidence and severity of DPN.[14] Diagnosis of DPN can be supported by electrophysiology and quantitative sensory tests, though electrophysiological testing is usually needed only for patients with atypical clinical features.⁹ Several devices are currently available to enable physicians to evaluate and perform quantitative nerve conduction velocities and are listed in Table 7.

Table 7. Select diagnostic tools used to evaluate DPN

Table 8. Diabetic peripheral neuropathy severity scale [1]

Conclusion

Amputation and foot ulceration are the most common consequences of diabetic neuropathy and are major causes of morbidity and disability in patients with diabetes. Symptoms of DPN may be subtle and asymptomatic; therefore, formal screening tests identifying early manifestations of the disease are imperative to help decrease the morbidity of this disease. Several screening tools can be utilized to identify the foot at high risk for developing ulcerations and amputations and thus help prevent the serious complications associated with DPN.

References

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