Numbness in the left thumb may be caused by a herniated disc, and similar symptoms can be caused by localized rheumatoid arthritis or gout. Incorrect sitting posture or degenerative changes in the lumbar spine can lead to a herniated disc, which can compress the blood vessels and nerve roots in the back, resulting in impaired blood circulation in the lower extremities, as well as nerve damage and lack of nutrition, resulting in local sensory abnormalities that cause numbness. The presence of rheumatic or rheumatoid arthritis causes inflammatory reactions in the joints, which can lead to adhesions between the joints and can also lead to nerve damage and affect blood circulation, thus causing numbness. If gout occurs after a poor diet, numbness can be caused by the deposition of uric acid in the joints and damage to the joints, which can also affect the normal function of the big toe.