hi, thanks for consulting HCM.I can give to two differential diagnosis after seeing your history. -Flea bites can be grouped in lines or clusters. If you are particularly sensitive to flea bites, they can lead to a condition called papular urticaria (where a number of itchy red lumps form). Bullae may also develop.Fleas from cats and dogs can often bite below the knee, commonly around the ankles. They may also affect the forearms if you have been stroking or holding your pet. -Venous stasis causes pooling red blood cells to stain the skin of the ankles from the inside out, creating reddish or brown patches on the ankles,Venous stasis refers to the medical condition resulting when leg veins lose their ability to carry blood back up the legs toward the heart. Venous stasis can occur due to injury, surgery or poor circulation, and it can indicate the presence of life-threatening blood clots in the deep veins. Prompt medical attention is required to rule out deep vein thrombosis and to obtain medication or other treatment to alleviate venous stasis before it progresses to a chronic or ulcerative stage. thank you.