Leg pain is a very common symptom and can arise from many causes, most often musculoskeletal problems. However, when leg pain appears suddenly without any clear injury, it deserves extra caution.

Although Mr. A was in his seventies, he was otherwise in good condition and exercised regularly. Even during the pandemic, he continued to hike every day or work out at home. More than a month ago, he suddenly noticed that his left leg felt cold, followed by pain. The pain then gradually eased, so he did not pay much attention to it. Later, however, he found that his left calf felt weak and tired when walking, and after five to ten minutes he had to stop and rest. At first he assumed he had strained a muscle and expected it to recover with rest, but after two weeks there was still no improvement and the problem was preventing him from exercising, so he eventually sought medical advice.

Initially he thought the problem was musculoskeletal, but investigations did not reveal any obvious orthopaedic cause. His doctor did notice that the left leg was particularly cold and suspected a circulation problem, so he was referred to vascular surgery.

The vascular surgeon found that the pulse in the left leg was absent, while the pulse at the wrist was very irregular. After a series of tests, it was discovered that an artery below the knee had become severely blocked by a clot. The clot had formed because of an irregular heart rhythm and had then travelled with the bloodstream from the heart to the left leg, where it became lodged, causing acute arterial embolism.

The coldness and weakness in the left leg were due to inadequate blood supply. If the blockage is severe, it can lead to acute tissue death and may even result in amputation.

The doctors first used medication to stabilize his atrial fibrillation and then performed a minimally invasive vascular procedure to remove the clot from the left leg. Modern technology has led to the development of dedicated clot-removal catheters, about the size of a bamboo skewer, that can be inserted into the artery to aspirate the clot. Compared with older open surgery, in which the artery had to be opened directly to clear the clot, this greatly reduces the degree of trauma.

One day after the procedure, Mr. A was walking normally again and his previous leg pain had disappeared. To reduce the chance of further clot formation, however, he needed ongoing blood-thinning medication and follow-up for atrial fibrillation.

Sudden leg pain should never be ignored.

Author: Honorary Clinical Associate Professor, Department of Surgery, The University of Hong Kong; President, Vascular Health Foundation