Hello,
I have gone through your query and understand your concern.
There are plenty of causes for ankle and foot swelling.
As it is unilateral, it is more often due to local causes than systemic.
Some common causes we have to think of are
1. Local infection in foot or ankle like Cellulitis
2.
Venous insufficiency or
varicose veins
3. Deep vein thrombosis
4. Insect bite or sting on the foot or ankle
History of swelling and associated symptoms like pain,
fever etc.. are very important in diagnosing the cause for unilateral swelling in leg.
You need further physical examination and investigations like
complete blood count, ESR, Doppler
Ultrasound study.
Depending on the cause, treatment varies. For example if the swelling is due to cellulitis, it can be treated by Antibiotics and NSAIDS.
If the swelling is due to varicose veins, it can be controlled by compression banding or Stripping of varicose veins.
Hope this helps.
Please write back for further queries.
Wishing you good health.