Legs may swell for numerous reasons. Some of the possible diagnoses are listed in this leaflet.
What do you mean by swollen legs?
It does cover a multitude of options, doesn't it? One leg or both legs could be swollen. If both legs, it could be symmetrical or worse on one side. A specific part of the leg(s) could be swollen, or the entire leg(s). It could have come on suddenly or gradually. It could be there all the time, or it could come and go. It could be painful nor not. Taking into account all these things will help narrow down the likely cause.
Where could the swelling be coming from?
Most often the swelling comes from fluid in the spaces between the cells in the legs, and when this is the case it is called oedema. It is called pitting oedema if a dent made when you press with your fingertip stays in the skin after you have taken the fingertip away.
The swelling could also be coming from skin, bones, tendons - really from any tissue of the leg.
What could be the cause?
Sometimes it is obvious ... you are tripped up in a football game, or you fall over an uneven pavement stone, and your leg is immediately painful, and swells up soon after. Either you have a sprain or you have broken a bone. But in other situations, both legs gradually become swollen over a week or a month, don't hurt, and you have no idea where the swelling has come from.
If both legs are swollen to the same level, this is likely to be oedema. There are multiple causes for this, including:
Further reading and references
Management of chronic heart failure; Scottish Intercollegiate Guidelines Network - SIGN (2016)
Trayes KP, Studdiford JS, Pickle S, et al; Edema: diagnosis and management. Am Fam Physician. 2013 Jul 1588(2):102-10.
Wiig H, Swartz MA; Interstitial fluid and lymph formation and transport: physiological regulation and roles in inflammation and cancer. Physiol Rev. 2012 Jul92(3):1005-60. doi: 10.1152/physrev.00037.2011.
Deep vein thrombosis; NICE CKS, April 2013 (UK access only)
Cellulitis - acute; NICE CKS, July 2015 (UK access only)
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