Small lumps on the thumb may be tendon sheath giant cell tumor, chondroma, dominant tendon sheath cyst, rheumatoid arthritis, lipoma and other diseases. 1. Giant cell tumor of tendon sheath: the cause of this disease is unknown, or related to inflammatory stimulation, trauma, genes and other factors. Mostly in the fingers, wrists, knees, feet and other parts of the attack, the lesion of the thumb will grow single or multiple lumps, with the hand touching the hard texture, the size of the lumps such as pea-like. 2. Chondrosarcoma: this disease often occurs in the fingers or palm of the hand, the clinical characteristics of the presence of a lump without pain, the growth rate of the lump is slow, the texture is relatively hard. When it appears in the thumb, it looks like a small lump from the outside. 3. dominant tendon sheath cyst: the disease occurs in the thumb, finger, wrist and other parts. When the disease occurs, a hemispherical lump will grow in the superficial subcutaneous area, which is smooth and soft to touch. 4. Rheumatoid arthritis: Rheumatoid arthritis is an immune system disease, there can be stiffness, swelling and other symptoms of the joints, invasion of small joints, swelling in the wrist, metacarpal fingers or interphalangeal joints. 5. Lipoma: It is a benign tumor of soft tissues, which is a tumor of normal fat-like tissues, usually a painless lump of small size, when a lump appears, it should be consulted promptly. When you find a small lump on your thumb, you can’t delay the treatment, you should go to the hospital in time.