We just came back from a long trip to the West Coast to take our eight-year-old daughter to a special arthritis clinic for kids. We thought she had arthritis but it turns out she has something else called venous malformation. The team there said it was rare and hard to detect but there were a few clues to help them out. They never did tell us how they could tell the difference. Without having her records, can you tell us why they were able to make the distinction?

Arthritis in children and venous malformation can present clinically with such similarity, it is very difficult to make the distinction. The knee becomes swollen and tender. Swelling and stiffness cause the knee to bend (unable to straighten fully). Loss of motion and stiffness result in a shortened leg on that side.

Juvenile idiopathic arthritis is a chronic condition of joint swelling and inflammation. The term ‘idiopathic’ tells us there’s no known cause. Venous malformation is as the name describes. Venous refers to the veins (blood vessels that return blood to the heart). The malformation is a jumble of veins often forming a clump or circle of veins. The effect of the malformation is to slow the blood down and keep it from moving through the area as it should.

Both conditions present with joint pain and swelling. When venous malformation causes these symptoms in a child, the natural diagnostic suspicion is for the more common juvenile idiopathic condition. Knee venous malformation is so rare, it is not easily recognized. But with careful study, it is possible to identify some characteristics of knee venous malformation that might be the tip off that it’s not arthritis.

MRIs and ultrasound studes are very helpful. These tests show blood filling in spaces within the muscles. This is a characteristic sign of venous malformation. Combining the results of imaging studies with biopsy of the tissue mass helps make the differentiation of venous malformation from juvenile idiopathic arthritis.

Sometimes the diagnosis isn’t made until the child is treated for arthritis without success. The more difficult cases are when the symptoms improve with antiinflammatories used for arthritis so it looks like the right diagnosis was made. It isn’t until the child is taken off the medication and the symptoms come back that a second (or third) look help reveal the true problem.

Other differentiating factors are very subtle. For example, juvenile idiopathic arthritis often affects all the large joints (knees, ankles, wrists, and elbows). Venous malformation presents at the knee most of the time. Lab tests may show some differences that can be helpful but this is not 100 per cent accurate.

Most of the time it’s the imaging studies that help define the problem. And because knee venous malformation is congenital (present at birth), the earlier MRIs are used the sooner the problem is identified correctly. Early recognition doesn’t always happen because symptoms don’t develop right away at birth. Some children don’t develop visible problems until years later.

There’s one other important clinical finding that can help tell these two conditions apart. Although both conditions cause joint pain and swelling, with knee venous malformations, there are often some skin changes that can be seen. The veins become more prominent on that side. There may be swelling above the kneecap. And the skin around the knee looks blue in color.

Knowledge of these differences can help the physician recognize the true underlying problem. Early diagnosis and treatment can help improve results. It sounds like your team of experts were well-informed and able to get to the bottom of the problem quickly!