Diagnosis and Treatment
The diagnosis of diabetic neuropathy is typically based on the presence of characteristic symptoms as well as findings on a physical exam (Feldman 2012c; National Diabetes Information Clearinghouse 2009; Morales-Vidal 2012). A questionnaire called the Michigan Neuropathy Screening Instrument or MNSI that asks “yes” or “no” questions about common symptoms of diabetic neuropathy, such as lower extremity numbness, pain, sensitivity, dryness, weakness, difficulty walking, and loss of temperature sensation is often used to help identify symptoms of diabetic neuropathy (Edwards 2008; Feldman 1994). However, the presence of clinical symptoms alone is not the most reliable indicator of diabetic neuropathy (England 2005). As a result, these symptoms should be correlated with a focused physical exam that looks for signs of a neurological deficit.
Common physical exam findings indicative of diabetic neuropathy include the presence of dry skin, ulcers or infections on the feet, diminished/absent vibration sensation at the big toe, and reduced or absent ankle reflexes (Feldman 1994; England 2005; Feldman 2012c; Tesfaye 2010; Edwards 2008; Meijer 2005). Other signs that may be observed are diminished sensation in the feet to pin pricks, muscle weakness/wasting, and diminished sensitivity to temperature (Feldman 2012c). Further information can be obtained by performing nerve conduction studies or electromyograms on the foot, both of which are techniques that measure the activity of nerves; abnormal results on these tests suggest the presence of diabetic neuropathy (National Diabetes Information Clearinghouse 2009; American Diabetes Association 2012; England 2005).
The signs of autonomic diabetic neuropathy can also be diagnosed on a physical exam. The effects of diabetic neuropathy on the nerves that govern circulation can be measured by checking the variability of the heart rate upon exertion and by checking blood pressure changes due to changes in body position, also known as orthostatic blood pressure (Morales-Vidal 2012; Tesfaye 2010; Edwards 2008).
One of the mainstays of treatment of diabetic neuropathy, and the most important strategy to prevent it, is improved blood glucose control (Callaghan 2012a; Edwards 2008; Feldman 2013; National Diabetes Information Clearinghouse 2009; Topiwala 2012). Pharmacologic treatments for diabetic neuropathies can focus on either the underlying mechanism or trying to relieve the symptoms; many conventional therapies fall into the second group (Edwards 2008).
Painful diabetic neuropathy is typically treated using a variety of different medications. Pregabalin (Lyrica®), an anticonvulsant, is often the first treatment tried (Topiwala 2012). Common side effects include dizziness, vertigo, blurred vision, sedation, and problems with coordination (Feldman 2013). Another medication that has been approved by the Food and Drug Administration (FDA) for the treatment of diabetic neuropathic pain is duloxetine (Cymbalta®), a serotonin-norepinephrine reuptake inhibitor (National Diabetes Information Clearinghouse 2009; Ziegler 2009). The mechanism(s) by which duloxetine relieves pain are unclear, but blockade of neuronal sodium channels is thought to be involved (Wang 2010). The most common side effects of duloxetine are nausea, dizziness, somnolence, dry mouth, constipation, and decreased appetite (Ziegler 2009). Other medications that, while not specifically licensed for the treatment of diabetic neuropathy, are commonly used include bupropion (Wellbutrin®), paroxetine (Paxil®), amitriptyline (Elavil®), doxepin (Sinequan®), venlafaxine (Effexor®), and citalopram (Celexa®) (National Diabetes Information Clearinghouse 2009; Ziegler 2009; Topiwala 2012; Feldman 2013). Although these medications are all antidepressants, they may provide relief to those suffering from diabetic neuropathy even in the absence of depression (National Diabetes Information Clearinghouse 2009).
Medications used for treating seizures, such as gabapentin (Neurontin®), a GABA analog, may also help relieve diabetic neuropathic pain in some cases (Ziegler 2009). The mechanism(s) by which gabapentin relieves pain have not been well defined (Tanabe 2008). Opioid medications, such as tramadol and oxycodone, may also provide effective pain relief (National Diabetes Information Clearinghouse 2009; Ziegler 2009; Topiwala 2012; Feldman 2013).
Conventional treatments may also be used to help with the other complications of diabetic neuropathy. For example, people that suffer from delayed gastric emptying can take erythromycin (Eryc®) and metoclopramide (Reglan®) to speed digestion (National Diabetes Information Clearinghouse 2009). Erectile dysfunction can be treated using sildenafil (Viagra®), tadalfil (Cialis®), and vardenafil (Levitra®) (National Diabetes Information Clearinghouse 2009; Topiwala 2012).