First, there were mosquito bite-like lumps on the foot, followed by itching and pus discharge.

　　Large purplish-red patches on an elderly person's arm may result from physiological factors, or could be caused by pathological conditions such as allergic purpura or thrombocytopenic purpura. Treatment options include general supportive measures and medication. Specific details are as follows:

　　I. Physiological Factors

　　With advancing age, blood vessels in the elderly gradually lose elasticity and become more fragile, which may lead to capillary rupture and result in large areas of bruising on the skin. Appropriate physical exercise can help improve immune function.

　　II. Pathological Factors

　　1. Allergic Purpura

　　This is typically an allergic inflammation affecting the skin, small arteries, and other organs. Causes may include infections, drug allergies, pollen allergies, etc. It may cause bluish-purple bruising on the body. Treatment may include medications such as levocetirizine hydrochloride tablets or diphenhydramine hydrochloride tablets, used under a doctor’s guidance.

　　3. Thrombocytopenic Purpura

　　This condition may be associated with immune system dysfunction or infections. After onset, it may lead to mucocutaneous bleeding that appears purplish-red. Treatment may involve taking medications such as platelet-increasing capsules according to medical advice.

　　In addition to the above causes, such symptoms may also be due to myelodysplastic syndromes, hemophilia, leukemia, or other conditions. It is important to get adequate rest and avoid excessive fatigue.