Swelling in only one leg has been a frequent patient presentation in our clinic and is a problem that usually requires a multi-step evaluation before making a diagnosis. Some of our patients have already had an ultrasound elsewhere that showed no evidence of blood clots. But, a repeat ultrasound study in our office occasionally does show evidence of a clot or some sort of problem with the venous system. In fact, since vein issues and clots are the most common cause of swelling in only one leg, these problems should be investigated quickly and thoroughly. When the ultrasound exam from calf to groin is truly negative for any venous disease then we begin to search for other causes.
Approximately, half of patients with single leg swelling will have information in their medical history that yields clues as to how to proceed with the investigation. Questions should be asked about a prior blood clot, past trauma, orthopedic procedures or other abdominal, pelvic or lower extremity surgical procedures. This includes any prior radiation therapy to the pelvis or rectum. A single severe or recurrent infection of the foot or leg could also be the cause of changes in how fluids (which normally flow up the leg in the fine lymphatic channels of the skin and fatty tissues) become obstructed and back up causing swelling. Once these potential issues have been ruled out, determining if there is a history of weight loss, night sweats, joint/bone aches are important.
Since these inquiries still often result in a negative history, the physical exam becomes critical. In women, a pelvic exam, and in men, a rectal and prostate exam should be documented. The pattern of the swelling often suggests cause. Circumferential edema of an entire leg points to a groin or pelvic source. Involvement of the foot and toes suggests local lymphatic fluid back up often seen in obesity and is more common in women. Sometimes this fluid accumulation occurs due to a change in walking mechanics.
The next aspect of investigation involves focusing on the pelvis. Basic lab work is helpful as well as stool tests for blood. However, pelvic imaging is required. While ultrasound is inexpensive and safe, pelvic ultrasound imaging looking for a cause of swelling in one leg is usually not helpful. CT or MRI scans can uncover causes for single leg swelling such as gynecologic masses, and rectal or prostate malignancies.
Finally, intravenously placed ultrasound catheters have recently been used to identify internal or external compression of the deep veins in the pelvis causing obstruction to blood flow and swelling in one leg…even when the conventional office ultrasound exam is normal. While this breakthrough technology performed in a cath lab is very sensitive in finding changes in the deep veins, we are seeing a number of “positive” intravenous ultrasound exams resulting in stents being placed inside these veins, without improvement in swelling. In other words, we do not yet have guidelines that will reliably predict improvement of leg swelling when these deep pelvic vein lesions are treated with stents.
In summary, single leg swelling can be a puzzle to diagnose. However, blood clots in the veins, leg or foot infections, followed by pelvic malignancies (or their previous treatment with radiation) are the most common diagnoses we make.