The fat arm may be caused by the following mechanisms: 1. It may be due to the patient’s own excessive obesity, if the patient is excessively obese, there will be obvious fat deposits not only in the upper limbs, but also in the waist and abdomen, lower limbs, etc., which in turn causes the limbs to be thicker in diameter. 2. This situation may be caused by the patient’s own fat deposition characteristics, that is, some patients will gain weight in the upper limbs when they are fat, and some patients will gain weight in the waist and abdomen first. This is due to individual differences. 3. This condition may be caused by the developed muscles of the upper limbs before the patient becomes fat, if the patient has developed muscles in the upper limbs before, once the fat deposits are produced under the skin here, it will quickly lead to very fat upper limbs. 4. Some patients do not have a high fat content in the upper limbs, but have severe swelling in the upper limbs, which causes them to look very fat.