I just learned a bit of medical jargon for something I’ve observed but didn’t have a phrase for: symptom locking. Unfortunately, it doesn’t seem to have hit the medical journals yet, but I hope to see it in the future, because I’m sure it applies to other conditions than just XLH, and it’s important for really understanding the trajectory of symptoms after starting a new treatment.
I couldn’t find an official definition, but my understanding is that symptom locking describes a situation where a patient has a certain symptom at the beginning of treatment, and then still has that symptom after treatment even though the treatment has actually improved the situation. The problem is that we’re not simple machines, with only one thing going at on any given moment. So the improvement in the symptom after treatment is not showing up in any data, and even the patient may not recognize the improvement, because other factors besides the underlying condition are contributing to the ongoing symptom, making it seem unchanged.
Yeah, that’s confusing, isn’t it? But if you’ve gone from old (or no) treatment to burosumab, you’ll recognize the pattern of symptom locking. You had pain/fatigue before treatment, and you still have pain/fatigue after treatment, but the difference is that you were more active after treatment and were able to accomplish so much more. It was that extra activity that masked what would otherwise be a noticeable decrease in the pain/fatigue.
During the clinical trials for burosumab, we had to complete standard surveys on pain and fatigue at the beginning for a baseline, and then we repeated the surveys every so often, in an attempt to capture any improvements after treatment. And what the surveys revealed (to everyone’s surprise) was that in many cases, the pain/fatigue did NOT appear to change much, if at all. At least initially, the data seemed to indicate that treatment had no significant effect on pain/fatigue (although if I remember correctly, later data showed a slight improvement in both).
Except we patients all knew that didn’t accurately describe our experience, and there really was a substantial improvement in both our pain and fatigue levels. What happened was that, as people who live with chronic pain, we were used to whatever our baseline pain/fatigue levels were, and were accustomed to ignoring that level of discomfort. It was only when we exceeded those levels that we would notice, and be forced to take a break to recover. Our consciousness of that pain/fatigue was locked in at that level (“symptom locking”), so as the burosumab normalized our phosphorus and reduced our pain/fatigue, it took more activity to hit that pain/fatigue level that would force us to take a break, and we kept going until we hit that locked-in level. Our pain/fatigue levels stayed essentially the same, but we we were able to do so much more before they forced us to rest, and we were so much less limited in our daily lives! Our symptoms were locked in—the levels of pain/fatigue—while other factors, like activity, changed, but were not captured by the data to explain why the pain/fatigue hadn’t improved. Patients knew, but the data didn’t reflect, that initially the pain/fatigue occurred after very limited activity, and later on, after treatment, the pain/fatigue occurred after significantly increased activity.
I remember being really frustrated by this gap in the data collection during the clinical trials, because the surveys ONLY asked what our pain/fatigue levels were, without any questions about changes in our daily lives that might have contributed to the pain/fatigue levels. Even as I was completing the surveys, I knew that they weren’t truly reflective of my experience, and they would produce misleading results that under-quantified the effectiveness of the treatment. Once, the timing was such that I had to answer the surveys during the week when I’d been traveling across-country, something that, in the best of circumstances, can be painful/tiring. So my pain/fatigue levels were a little higher that week than during the more sedentary periods when I’d completed previous surveys on the topic. I kept wishing I could put an asterisk next to my answers to explain that yes, I was in increased pain that week, but I’d been doing a bunch of painful stuff that I didn’t normally do. I would have also liked to explain that even though my pain/fatigue was higher than usual that week, it was still substantially less than it would have been during a travel week prior to burosumab treatment. I remember vividly that when I got home from that particular trip, I was exhausted and expected to be bedridden for at least three days to recuperate, but after just one good night’s sleep, I bounced back completely the next day! And yet, when looking at just the pain/fatigue data, without any awareness of my activity levels, it would appear that I was doing worse than before treatment.
So, add that to your personal dictionary: symptom locking. And if your clinician isn’t already familiar with the concept, make sure they’re asking the right questions (h/t to Dr. Kassim Javaid) about changes to your health: not just “what’s your pain/fatigue level,” but “what activities that you want to do are being limited by your pain/fatigue?” Treatment should not be about some theoretical, optimal pain/fatigue level, but about the quality of life you can have before the pain/fatigue limits you!
***
Please note that the author is a well-read patient, not a doctor, and is not offering medical or legal advice.
If you’d prefer to read this blog as a newsletter, sent straight to your inbox, please sign up here.