Sometimes one disease mimics another one so closely, it is difficult to tell them apart. That’s the case with these two separate knee problems that look very similar. 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.
By taking a look back, it’s possible to identify some characteristics of knee venous malformation that might be the tip off that it’s not arthritis. Of course, as the old saying goes: “Hindsight is 20-20.” In other words, it’s much easier to look back at what was really going on but difficult to understand at the time it was happening.
Even when the malformation creates a mass that is removed, the jumble of blood vessels can look so much like a hemangioma (benign blood tumor) the diagnosis remains clouded. Sometimes it’s not until the mass grows back or the family seeks a second opinion that the real diagnosis is made.
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.
There is one recent study we can cite in giving you an idea how rare the problem is and how often misdiagnosis occurs. This study took place at a large children’s hospital in the Northeast (Boston Children’s).
A review of their records for an 11 year period of time showed that of all the children seen at the hospital for 11 years, only 56 children had venous malformations of the knee. Six of those children were treated as if they had juvenile idiopathic arthritis before the accurate diagnosis was made. That’s a misdiagnosis rate of 11 per cent (very high).
Your situation sounds fairly typical given the rarity of the venous malformation condition. Given the similarity of signs and symptoms, tt’s easy to make the mistake of thinking the child has arthritis. Thankfully your granddaughter’s diagnosis has been cleared up and the correct treatment applied.