Neurology · Peripheral Neuropathy
The facts most likely to be tested
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Diabetes mellitus is the most common cause of peripheral neuropathy, typically presenting as a length-dependent, symmetric, distal sensory polyneuropathy described as a stocking-glove distribution.
Guillain-Barré syndrome presents as an acute, ascending, symmetric muscle weakness often following a Campylobacter jejuni infection, characterized by albuminocytologic dissociation on lumbar puncture.
Vitamin B12 deficiency causes subacute combined degeneration of the spinal cord, manifesting as symmetric paresthesias, loss of vibration and position sense, and upper motor neuron signs.
Charcot-Marie-Tooth disease is the most common hereditary motor and sensory neuropathy, classically presenting with distal muscle atrophy, pes cavus, and hammer toes.
Mononeuritis multiplex is a vasculitic neuropathy characterized by the sudden onset of asymmetric, painful, multifocal sensory and motor deficits in the distribution of individual peripheral nerves.
Alcoholic neuropathy results from a combination of direct neurotoxicity and thiamine deficiency, typically presenting with burning pain and paresthesias in the lower extremities.
Electromyography (EMG) and nerve conduction studies (NCS) are the diagnostic tests of choice to differentiate between axonal degeneration and demyelinating processes.
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A 58-year-old male with a 15-year history of poorly controlled type 2 diabetes presents to the clinic complaining of persistent burning pain in both feet. He describes the sensation as if he is walking on cotton balls, which worsens at night. Physical examination reveals diminished pinprick and vibration sensation in a stocking-glove distribution bilaterally. Ankle reflexes are absent on both sides. There are no signs of motor weakness or gait instability.
What is the most appropriate initial pharmacologic treatment for this patient's neuropathic pain?
Pregabalin or Gabapentin
The patient presents with classic diabetic distal symmetric polyneuropathy; first-line treatment for neuropathic pain in this condition includes gabapentinoids or SNRIs (e.g., duloxetine).
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Etiology / Epidemiology
Diabetes mellitus is the most common cause; chronic alcohol use and B12 deficiency are major contributors.
Clinical Manifestations
Symmetric stocking-glove sensory loss; distal paresthesias and loss of ankle jerks.
Diagnosis
Electromyography (EMG)/Nerve Conduction Study (NCS) is the gold standard for characterizing axonal vs. demyelinating patterns.
Treatment
Gabapentin or Pregabalin are first-line; avoid opioids for chronic neuropathic pain.
Prognosis
Strict glycemic control (HbA1c <7.0%) is the only intervention proven to slow progression.
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Epidemiology & Etiology
Peripheral neuropathy is most frequently secondary to metabolic syndrome and diabetes. Other common etiologies include chemotherapy-induced (e.g., vincristine), uremia, and Guillain-Barré syndrome. Nutritional deficiencies, specifically B12 and thiamine, must be ruled out in alcohol-dependent patients.
Pertinent Anatomy
The longest axons are affected first, explaining the stocking-glove distribution. Damage to large-fiber nerves results in loss of vibration and proprioception, while small-fiber damage causes burning pain and temperature loss.
Pathophysiology
Metabolic stress leads to axonal degeneration (dying-back neuropathy) or segmental demyelination. Hyperglycemia induces oxidative stress and formation of advanced glycation end-products, damaging the vasa nervorum. This microvascular ischemia results in progressive nerve fiber loss.
Clinical Manifestations
Patients present with distal sensory loss, burning pain, and allodynia. Physical exam reveals diminished ankle jerks and impaired monofilament testing. Red flags include asymmetric onset, rapid progression, or motor weakness, which suggest mononeuritis multiplex or inflammatory causes.
Diagnosis
EMG/NCS is the gold standard to differentiate axonal loss from demyelination. Laboratory workup must include HbA1c, TSH, and serum B12/methylmalonic acid. A nerve biopsy is reserved for suspected vasculitis or amyloidosis.
Treatment
Pregabalin or Gabapentin are the first-line agents for neuropathic pain. Duloxetine is preferred if comorbid depression is present. Avoid opioids due to high risk of dependence and lack of efficacy in chronic neuropathic pain.
Prognosis
Progression leads to foot ulcers and increased risk of amputation. Annual podiatric exams and daily self-foot inspections are mandatory to prevent secondary infection.
Differential Diagnosis
Guillain-Barré: rapid ascending paralysis
B12 Deficiency: subacute combined degeneration
Charcot-Marie-Tooth: hereditary high-arched feet
Lyme Disease: radiculopathy following tick bite
Vasculitis: asymmetric mononeuritis multiplex