Purple spots on the thighs indicate subcutaneous bleeding on the thighs. If purple spots appear on the thighs, you need to go to the hematology department for routine blood tests and coagulation routine to find the cause of subcutaneous bleeding, if the routine blood tests and coagulation routine are not abnormal, the biggest possibility is allergic purpura or vitamin C deficiency, which can be treated with vitamin C supplementation. If the platelet count decreases, it is possible that the subcutaneous bleeding is caused by thrombocytopenia, which requires further examination in the hematology department, including bone marrow aspiration, to confirm the diagnosis before giving the appropriate treatment. If the diagnosis of immune thrombocytopenia is confirmed, the preferred treatment is glucocorticoid therapy.