Numbness of the hand is most commonly caused by the following conditions:
Cervical disc lesion: This may be associated with pain in the neck and weakness of the arm.
Peripheral neuropathy: common conditions causing this are diabetes, Vit. B deficiency, etc.
Vascular insufficiency: Atherosclerosis of arteries, spasm, etc, may cause vascular insufficiency.
Peripheral neuropathies are most commonly caused by diabetes mellitus, but there are many other diseases as well and it needs to be well investigated to find out the cause.
Vascular insufficiency is another common cause, and is more common in those above 60 and in smokers.
You should consult your health provider or a neurologist if possible and get yourself checked up to identify the cause in your case. You may need a CT or MRI of the brain and spinal column and tests for muscle conductivity and nerve velocity, etc. You may look up this site for a discussion on problems similar to yours: http://www.thehelpinghand.com/discus/messages/4/21.html?1159491281
For your general health, you should also do the following annual tests:
Thyroid hormone tests.
Random blood sugar
Test for occult blood in stool
US of the whole abdomen.
Liver function tests.
Kidney function tests
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