This is something that can happen, where you have a deep foot ulcer, and rightly so, your doctor is concerned and suspicious for a bone infection because of how deep the ulcer is. An x-ray is ordered, which is negative. Well, x-rays are not very sensitive for bone infection, so next, a MRI (magnetic resonance image) is ordered. This is a very sensitive and expensive test, but sometimes this also comes back inconclusive. The report will have a bunch of jargon and in the end it will say something like “please clinically correlate” or “consider bone biopsy”. What it really means is “I’m not sure”. Although a bone biopsy is the gold standard of diagnoses for osteomyelitis, there is evidence that challenges this standard that is different topic altogether . Welcome to the gray zone of medicine.
Dealing with the gray zone
There are gray zones everywhere, in every aspect of medicine and in every specialty. Some gray zones are bigger than others. As doctors, we LOVE it when a diagnosis is obvious, because then the treatment is obvious and we know exactly what to do. The HARD part is when the diagnosis is NOT obvious, in which case we have to really wrap our brain around every detail to see if it will sway us in one direction or another. Medicine is part art and part science, and I believe the art really comes out when dealing with a clinical situation in the gray zone. For diabetic feet where we are not sure if there is a bone infection or not, there are 3 basic strategies:
Pursue the diagnosis
If knowing the answer will change the course of treatment, then it is a good idea to go through with getting more imaging or a bone biopsy (a surgical procedure where we take a small sample of bone to send to the lab). Such examples would be situations where the options would be to try to save the foot… or foot amputation. A lot of factors weigh in the decision-making process including level of independence, presence of other medical problems, chance of recovery and success after surgery, experience of the doctor and the patient, and age. After considering all of the factors that come into play and we’re still not sure, then knowing if there is a bone infection may sway our decision. In this case it would make sense to go the extra mile.
Assume the diagnosis
If we consider all of the factors that come into play and it pushes us heavily to decide in one treatment plan, then knowing the diagnosis may not make a difference. A good example would be if somebody has had an ulcer at the tip of their pinky toe for years. The patient is fed up with this ulcer, and we know that an amputation of the pinky toe will have a good recovery without loss of function. Would it be worth trying to see if the bone at the tip of the pinky toe is infected? Ultimately the decision is up to the patient.
There can be situations where we have no idea if it is infected AND we are not sure if knowing the diagnosis would sway our decision for treatment. Well, we DO know that usually bone infections progress slowly. In this case, we might want to just continue treating the wound or ulcer, and see what happens over the next few weeks. We can take x-rays every couple of weeks to check on the bone. When we evaluate the wound, we can take notes on the amount of drainage, and if the drainage is decreasing or if the wound is getting smaller, we can probably assume that there is no bone infection. If the wound is not healing, or getting worse, or is draining more, then we might want to think about an MRI or bone biopsy.
So in summary, there are situations where we don’t know, and may not ever know if you have a bone infection in your foot. This seems frightening, but think about it like this: Let’s say that you do have a bone infection. Well, your infection is so small... that doctors are having a hard time finding it. If you are seeing your foot specialist regularly for your wound or ulcer, it will be watched carefully. As soon as the beginnings of an infection appears, it can be stopped before any real damage is done.
1) Meyr AJ, et al. Statistical reliability of bone biopsy for the diagnosis of diabetic foot osteomyelitis. JFAS Nov-Dec 2011;50(6):663-7