Thanks for answering my questions.
Now looking at your age,no history of past medical condition,no medications,symptoms,there is a possibility that you might be having venous insufficiency which is a condition where the valves in the leg veins are unable to pump blood to the heart which causes blood to pool below the defective valves.Now the reason for me mentioning venous insufficiency is because it presents with similar symptoms ,the swelling is present in one leg and it is common at your age.Though pain is also associated with this condition ,but some people do not present with pain in early stages.
Now there could be a possibility that this symptoms could be from deep vein thrombosis
as you have sedentary life style (sit at desk/computer job) and it also presents with unilateral swelling of leg but it also presents with acute pain,still it could be a possibility which is ruled out by sonogram of lower leg.
Now there is also a possibility that this could be from gout,though it mostly presents with acute pain in leg but chronic gout can present with similar symptoms so ask your physician to rule this possibility out.
Now another possibility which could similar symptoms like yours is lymphatic obstruction which is blockage of the lymph vessels that drain fluid from body tissues and facilitate immune system cell movement through the body.So ask your physician to rule this possibility too.
Now as you denied any history of trauma or tick bite so both causes are low in our list though it may also present with similar symptoms.
You did not mention any fever so cellulitis as cause of your symptoms is low in our list.
Now if it would have been any heart ,liver or renal problem leading to swelling ,it will most likely lead to swelling in both legs(bilateral) instead of right toe alone and as you mentioned that you have healthy living style at present,so these causes seems less likely.
Other possibility at your age,with similar symptoms,with no medical condition seems less likely.
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