Numbness and Tingling Health Article

Definition

Numbness and tingling are decreased or abnormal sensations caused by altered sensory nerve function.

Description

The feeling of having a foot "fall asleep" is a familiar one. This same combination of numbness and tingling can occur in any region of the body and may be caused by a wide variety of disorders. Sensations such as these, which occur without any associated stimulus, are called paresthesias. Other types of paresthesias include feelings of cold, warmth, burning, itching, and skin crawling.

Demographics

People of all ages experience episodes of numbness and tingling. These generally become more common as people age. Episodes of numbness and tingling are more common among people with diabetes, hypothyroidism, alcoholism, malnutrition, or who experience mechanical trauma, especially to their limbs, neck or spine.

Causes

Sensation is carried to the brain by neurons (nerve cells) running from the outer parts of the body to the spinal cord in bundles called nerves. In the spinal cord, these neurons make connections with other neurons that run up to the brain. Paresthesias are caused by disturbances in the function of neurons in the sensory pathway. This disturbance can occur in the central nervous system (the brain and spinal cord), the nerve roots that are attached to the spinal cord, or the peripheral nervous system (nerves outside the brain and spinal cord).

Peripheral disturbances are the most common cause of paresthesias. "Falling asleep" occurs when the blood supply to a nerve is cut off—a condition called ischemia. Ischemia usually occurs when an artery is compressed as it passes through a tightly flexed joint. Sleeping with the arms above the head or sitting with the legs tightly crossed frequently cause numbness and tingling.

Direct compression of the nerve also causes paresthesias. Compression can be short-lived, as when a heavy backpack compresses the nerves passing across the shoulders. Compression may also be chronic. Chronic nerve compression occurs in entrapment syndromes. The most common example is carpal tunnel syndrome, which occurs when the median nerve is compressed as it passes through a narrow channel in the wrist. Repetitive motion or prolonged vibration can cause the lining of the channel to swell and press on the nerve. Chronic nerve root compression, or radiculopathy, can occur in disk disease or spinal arthritis.

Other causes of paresthesias related to disorders of the peripheral nerves include the following:

• metabolic or nutritional disturbances, including diabetes, hypothyroidism (a condition caused by too little activity of the thyroid gland), alcoholism, malnutrition, and vitamin B₁₂ deficiency
• trauma, including injuries that crush, sever, or pull on nerves
• inflammation
• connective tissue disease, including arthritis, systemic lupus erythematosus (a chronic inflammatory disease that affects many systems of the body, including the nervous system), polyarteritis nodosa (a vascular disease that causes widespread inflammation and ischemia of small and medium-size arteries), and Sjögren's syndrome (a disorder marked by insufficient moisture in the tear ducts, salivary glands, and other glands)
• toxins, including heavy metals (metallic elements such as arsenic, lead, and mercury which can, in large amounts, cause poisoning), certain medications antibiotics and chemotherapy agents, solvents, and overdose of pyridoxine (vitamin B₆)
• malignancy
• infections, including Lyme disease, human immunodeficiency virus (HIV), and leprosy
• hereditary disease, including Charcot-Marie-Tooth disease (a disorder that causes wasting of the leg muscles, resulting in malformation of the foot), porphyria (a group of disorders in which there is abnormally increased production of substances called porphyrins), and Denny-Brown's syndrome (a disorder of the nerve root)

Paresthesias can also be caused by central nervous system disturbances, including stroke, transient ischemic attack (TIA), tumor, trauma, multiple sclerosis, or infection.