Peripheral Nerve Disorders

How peripheral nerves work

Peripheral nerves include:

• sensory nerves: carry touch, temperature, pain and position sense
• motor nerves: control muscles
• autonomic nerves: control heart rate, blood pressure, sweating, digestion and bladder

Damage can affect the nerve's insulation (myelin) or the nerve fiber itself (axon). The longest nerves, to the feet, are usually affected first, which explains the classic "stocking and glove" pattern.

Types of peripheral nerve disorder

Symptoms

Sensory

• numbness or reduced feeling, often in a stocking pattern
• tingling, pins and needles
• burning, stabbing or electric shock-like pain, often worse at night
• extreme sensitivity to touch (even bedsheets)
• poor balance, especially in the dark, from loss of position sense
• painless injuries and ulcers on the feet

Motor

• weakness, cramps and twitching
• foot drop, tripping
• difficulty with buttons or gripping
• muscle wasting

Autonomic

• dizziness on standing
• abnormal sweating
• digestive, bladder and sexual problems

Causes

• diabetes and prediabetes: the most common cause
• nerve compression: carpal tunnel, ulnar nerve at the elbow, peroneal nerve at the knee
• vitamin deficiencies: B12, B1 (thiamine), B6 (also toxic in excess), copper
• alcohol: direct toxicity plus poor nutrition (alcoholic neuropathy)
• medicines: chemotherapy (chemotherapy-induced neuropathy), some HIV drugs, metronidazole, isoniazid, amiodarone
• kidney failure, liver disease, hypothyroidism
• autoimmune and inflammatory: Guillain-Barre, CIDP, vasculitis, Sjogren's, lupus, celiac disease
• infections: shingles, HIV, Lyme disease, hepatitis C, leprosy
• inherited: Charcot-Marie-Tooth, hereditary amyloidosis
• blood disorders: paraproteins and myeloma
• toxins: lead, arsenic, solvents
• injury: cuts, fractures, stretch injuries
• idiopathic: no cause found in about a quarter to a third of people

Diagnosis

1. history and neurological exam: pattern, speed of onset, reflexes, vibration and pinprick sense, strength
2. blood tests: glucose and HbA1c, B12, thyroid, kidney and liver function, serum protein electrophoresis; others as needed
3. nerve conduction studies and EMG: distinguish axonal from demyelinating damage and locate compression
4. skin biopsy for small fiber neuropathy
5. imaging (MRI or ultrasound) for compression or root problems
6. genetic testing when an inherited neuropathy is suspected
7. nerve biopsy rarely

Treatment

Treat the cause

• control blood sugar
• replace vitamins
• stop alcohol or causative medicines
• release compressed nerves (splints, surgery)
• immune treatments for Guillain-Barre, CIDP or vasculitis

Relieve nerve pain

• medicines such as duloxetine, pregabalin, gabapentin, amitriptyline
• topical lidocaine or capsaicin
• avoid long-term opioids

Protect and support

• daily foot checks, well-fitting shoes, never walk barefoot, test bath water with an elbow
• physical therapy for strength and balance
• ankle-foot orthoses for foot drop
• fall prevention at home

Outlook

Outcomes depend on the cause. Nerves can regenerate slowly (about 1 mm a day) if the cause is removed. Compression neuropathies often improve with treatment. Diabetic and inherited neuropathies are usually long-term but can be slowed. Guillain-Barre syndrome usually improves over months.

Frequently asked questions

What are the symptoms of peripheral nerve damage?

Common symptoms include numbness, tingling, burning or shooting pain, sensitivity to touch, weakness, cramps and balance problems. They usually start in the feet and may spread to the hands. Some people have dizziness, sweating changes or digestive problems.

What is the most common cause of peripheral neuropathy?

Diabetes is the most common cause. Other frequent causes include nerve compression (such as carpal tunnel syndrome), vitamin B12 deficiency, heavy alcohol use, chemotherapy, kidney disease and inherited conditions. Some cases have no known cause.

How is peripheral neuropathy diagnosed?

Doctors take a history, examine sensation, strength and reflexes, and order blood tests for causes such as diabetes and B12 deficiency. Nerve conduction studies and EMG measure nerve function. A skin biopsy can diagnose small fiber neuropathy.

Can peripheral nerve damage be reversed?

Sometimes. If the cause is treated early, such as releasing a compressed nerve or correcting B12 deficiency, nerves can recover slowly. Long-standing damage from diabetes or inherited disease is often permanent, but progression can be slowed and pain managed.

When is numbness an emergency?

Get emergency care for sudden numbness or weakness on one side of the body, facial droop or slurred speech, weakness spreading up the legs over hours to days, or numbness in the groin with bladder or bowel problems.