Distal median nerve dysfunction

Alternative names

Neuropathy - distal median nerve

Definition

Distal median nerve dysfunction is a form of peripheral neuropathy (nerve dysfunction outside the central nervous system) affecting movement of or sensation in the hand, caused by damage to the distal median nerve.

For a common form, see carpal tunnel syndrome.

Causes, incidence, and risk factors

Dysfunction of a single nerve group, such as the distal median nerve, is classed as mononeuropathy. Mononeuropathy implies a local cause of the nerve damage, although occasionally systemic disorders may cause isolated nerve damage (such as the damage that occurs with mononeuritis multiplex).

Distal median nerve dysfunction occurs when the nerve is injured by trauma, entrapment, or inflammation. Entrapment involves pressure on the nerve where it passes through a narrow structure. Wrist fractures may injure the median nerve directly or may present a risk for entrapment of the nerve later on.

The nerve can also be compressed at the wrist by tendonitis, arthritis, or conditions that affect connective tissue or cause deposits in the tissues (such as multiple myeloma, pregnancy, acromegaly, and hypothyroidism). These mechanical factors may cause nerve disease, blocking blood flow to the area.

In some cases, no detectable cause can be identified.

Carpal tunnel syndrome, a form of median nerve dysfunction, is one of the more common localized peripheral neuropathies. Carpal tunnel syndrome may be associated with entrapment of the nerve following prolonged or repeated pressure on the wrist area (such as may occur with repetitive wrist movements such as those made when typing or using a computer). This is a fairly common occupational or recreational injury.

Symptoms

• Sensation changes of the thumb and first 2 fingers
  o Numbness, decreased sensation
  o Tingling, burning sensation
  o Waking up at night with wrist or hand pain (may be severe)
  
• Weakness of the hand
  o Dropping things
  o Difficulty grasping objects
  

Signs and tests
Examination may show decreased sensation in the thumb side (radial) fingers of the hand. There may be weakness of the thumb and difficulty using it to pinch.

Tests that reveal distal median nerve dysfunction may include:

• EMG (a recording of electrical activity in muscles)
  
• Nerve conduction tests