Polyneuropathies & Mononeuritis Multiplex

Essentials of Diagnosis

• Weakness, sensory disturbances, or both in the extremities

• Pain is common

• Depressed or absent tendon reflexes

• May have family history of neuropathy

• May have history of systemic illness or toxic exposure

General Considerations

• The cause of polyneuropathy or mononeuritis multiplex is suggested by the history, mode of onset, and predominant clinical manifestations

• Diffuse polyneuropathies

  • Include hereditary, metabolic, and toxic disorders; idiopathic inflammatory polyneuropathy (Guillain-Barré syndrome); and paraneoplastic peripheral neuropathies (that occur as a nonmetastatic complication of malignant diseases)

  • Lead to a symmetric sensory, motor, or mixed deficit, often most marked distally

• Multiple mononeuropathies (mononeuropathy multiplex) suggest

  • A patchy multifocal disease process such as vasculopathy (eg, diabetes mellitus, arteritis)

  • An infiltrative process (eg, leprosy, sarcoidosis)

  • Radiation damage

  • An immunologic disorder (eg, brachial plexopathy)

• Flaccid weakness that is most marked distally

• Dysfunction of sensory fibers causes impaired sensory perception

• Tendon reflexes are depressed or absent

• Paresthesias, pain, and muscle tenderness may also occur

Laboratory Tests

• Complete blood count

• Serum protein electrophoresis with reflex to immunofixation or immunotyping

• Determination of plasma urea and electrolytes

• Liver biochemical tests

• Thyroid function tests

• Vitamin B₁₂ level

• Tests for rheumatoid factor and antinuclear antibody

• HBsAg determination

• Serologic test for syphilis

• Fasting blood glucose level and hemoglobin A_1c

• Urinary heavy metal levels

• Cerebrospinal fluid examination

Imaging

• Chest radiograph

Diagnostic Procedures

• Measurement of nerve conduction velocity

  • Can confirm the peripheral nerve origin of symptoms

  • Provides a means of following clinical changes as well as indicating the likely disease process (ie, axonal versus demyelinating neuropathy)

• Cutaneous nerve biopsy may help establish a precise diagnosis (eg, polyarteritis, amyloidosis)

• In about half of cases, no specific cause can be established

Medications

• Neuropathic pain may respond to

  • Analgesics, such as aspirin or nonsteroidal anti-inflammatory drugs

  • Gabapentin (300 mg orally three times daily, titrated up to a maximum of 1200 mg orally three times daily as necessary)

  • Pregabalin (50–100 mg orally three times daily)

• Duloxetine (60 mg orally once or twice daily) or venlafaxine (start 37.5 mg orally twice daily, and titrated up to 75 mg orally two to three times daily) may be helpful, especially in painful diabetic neuropathy

• Opioids or opioid substitutes may be necessary for severe hyperpathia or pain induced by minimal stimuli, but their use should be avoided as long as possible

• Episodic stabbing pains may respond to any of the following

  • Gabapentin (300–1200 mg orally three times daily)

  • Pregabalin (100 mg orally three times daily)

  • Carbamazepine (start 100 mg orally twice daily, and titrate up to 400 mg orally twice daily)

  • Amitriptyline (10–150 mg orally at bedtime daily, or other tricyclic antidepressants)

• Postural hypotension

  • Often helped by wearing waist-high elastic stockings and sleeping in a semierect position at night

  • Fludrocortisone reduces postural hypotension, but doses as high as 1 mg daily orally are sometimes necessary in diabetics and may lead to recumbent hypertension

  • Midodrine, an α-agonist, is sometimes helpful in a dose of 2.5–10 mg three times daily orally

• Erectile dysfunction can be treated with phosphodiesterase inhibitors (sildenafil, tadalafil, vardenafil)

• A flaccid neuropathic bladder may respond to parasympathomimetic drugs such as bethanechol chloride, 10–50 mg orally three or four times daily

Therapeutic Procedures

• Treatment of the underlying cause

Prevention

• Physical therapy helps prevent contractures

• Splints can maintain a weak extremity in a position of useful function

• Anesthetic extremities must be protected from injury

• To guard against burns, patients should do one of the following

  • Check the temperature of water and hot surfaces with a portion of skin that has normal sensation

  • Measure water temperature with a thermometer

  • Use cold water for washing or lower the temperature setting of the hot-water heaters

• Shoes should be examined frequently for grit or foreign objects to prevent pressure lesions

• Patients should avoid leaning on elbows or sitting with crossed legs for lengthy periods

• The use of a frame or cradle to reduce contact with bedclothes may be helpful for pain or dysesthesias

When to Refer

• When the diagnosis is uncertain

• For specialized diagnostic tests or for nerve biopsy

• For physical therapy