Although carpal tunnel syndrome is one of the most common causes of numbness and tingling in the hand, there are many other possible causes of these symptoms.
If a nerve is compressed, it can cause numbness in the area supplied by that nerve. For example, compression of your median nerve at the wrist causes numbness in your thumb, index, long, and half of the ring finger. You also might have weakness or atrophy (shrinking) of the muscles controlled by that nerve. If the nerve is compressed in the forearm, you might also note numbness in the palm of the hand at the base of the thumb.
Compression of your ulnar nerve at the wrist causes numbness of the little finger, part of the ring finger, and the little finger side of the palm. Tingling on the back of the hand near your little finger is an indication that the ulnar nerve might be compressed at the elbow.
Compression of your radial nerve in the forearm or wrist causes numbness on the back of the index finger, thumb, and the web space between them. This often is caused by trauma or by wearing a watch or bracelet that is too tight.
Nerve compression might not be occurring within the arm; these nerves actually come from roots in the neck, where narrowing of the canals through which they travel can cause numbness, tingling, pain, weakness, or other symptoms. Arthritis, infection, tumor, or other conditions can cause pressure on the spinal cord. The C6 nerve root supplies the thumb and index finger, C7 the long finger, C8 the ring and small finger, and T1 the wrist area opposite the thumb.
“Double crush” syndrome occurs when a nerve is compressed at more than one area (such as at the spine and the elbow, or the spine and the wrist).
Diseases of the central nervous system such as stroke and multiple sclerosis, or conditions like diabetes, alcoholism, or poisoning that cause “peripheral neuropathy” that does not follow a specific pattern also can cause hand and arm numbness.
Chemotherapy and vitamin deficiencies can result in numbness and tingling.
History, physical examination, and possibly other studies will be needed to determine the cause of your symptoms and the best way to address them.