Peripheral Neuropathy

Importance: Peripheral neuropathy, defined as damage to peripheral nerves, affects approximately 1% of adults worldwide. More than 200 causes of peripheral neuropathy exist, with symptoms ranging in severity from mild toe numbness to debilitating symptoms that can require a wheelchair. Diabetes is the most common cause of neuropathy, affecting approximately 206 million people worldwide. Observations: Peripheral neuropathy is typically length-dependent, which means that symptoms appear in the longest nerve axons (toes) and progress proximally over time. Peripheral neuropathy is typically symmetric and affects sensory axons more than motor axons. Diabetic neuropathy, which is often associated with both sensory symptoms, such as pain, tingling, or numbness; mild weakness; and autonomic symptoms, such as orthostatic hypotension, accounts for more than 50% of peripheral neuropathy in Western populations. Other causes of neuropathy include hereditary causes, such as Charcot-Marie-Tooth disease, toxic neuropathy from medications (chemotherapies [eg, cisplatin, paclitaxel, vincristine], amiodarone, or HIV nucleotide reverse transcriptase inhibitors [eg, stavudine, zalcitabine]); alcohol; vitamin deficiencies such as vitamin B12; and monoclonal gammopathies. Up to 27% of adults with neuropathy have no identifiable etiology for their neuropathy after diagnostic testing. Recommended initial testing includes blood glucose (for diabetes), serum B12 with metabolites (methylmalonic acid with or without homocysteine), and serum protein electrophoresis with immunofixation (for monoclonal gammopathies). First-line medications for neuropathic pain are the α2-δ calcium channel subunit ligands, such as gabapentin and pregabalin; serotonin norepinephrine reuptake inhibitors, such as duloxetine and venlafaxine; and tricyclic antidepressants, such as amitryptyline and nortriptyline. Pain often persists despite medical management. At least a 50% reduction in pain was observed in 38% of those with painful diabetic peripheral neuropathy receiving 1200 mg of gabapentin daily. Combination drug therapies for neuropathic pain may provide added benefit. The prognosis of peripheral neuropathy depends on its underlying cause, but complete reversal of nerve damage is uncommon even in cases for which there are available treatments. Conclusions and Relevance: Peripheral neuropathy affects approximately 1% of adults worldwide and may cause sensory, motor, and autonomic symptoms. Diabetes is the most common cause of peripheral neuropathy in Western countries. First-line therapies for neuropathic pain include gabapentin, pregabalin, duloxetine, and amitriptyline.