Restless Legs Syndrome (RLS) is a real condition, and a known potential side-effect of burosumab (and can also occur in XLH patients who are not on burosumab). I’d love to know if other chronic hypophosphatemias NOT treated by burosumab are also prone to the condition, but I’m not aware of any research into the question. I did reach out to one ENPP1 patient, who confirmed that both that patient and the one other ENPP1 patient they know both have experienced RLS, despite not being on burosumab (since their phosphate wasting has a different cause).
According to the National Institutes of Health, RLS “causes unpleasant or uncomfortable sensations in the legs and an irresistible urge to move them. Symptoms commonly occur in the late afternoon or evening hours, and are often most severe at night when a person is resting, such as sitting or lying in bed.” You can read more here.
From what I’ve read, the cause of RLS isn’t well understood, despite being fairly common. From my review of medical journal articles, it appears that RLS is associated with pregnancy, kidney disease, and Parkinson’s, among other common conditions. I found one study report about chronic kidney disease (CKD) patients that looked at phosphorus blood levels (among other factors), looking for correlations to RLS, and it did find a correlation between HIGH phosphorus blood levels and RLS. It’s not always possible to compare CKD patients’ phosphorus and FGF23 levels to those of XLH patients, because the biochemistry is different, but it does suggest an interesting research project that would compare XLH patients’ RLS symptoms at times of peak blood phosphorus levels to times of lowest blood phosphorus levels, either directly with blood tests or even indirectly by matching it to the burosumab treatment cycle, since the pattern of blood phosphorus rise and fall within the 28-day cycle of treatment is well known.
I’ve never been diagnosed with RLS, so I reached out to fellow XLHer Kelly Rushing (also a new member of the XLH Network board of directors, but writing here in her personal capacity, not on behalf of the Network), who graciously agreed to share her experience with RLS. Here’s what she had to say:
I look over at my phone in the darkness to check to see what time it will read. It’s 2:30am! I think to myself, it’s just going to be another one of THOSE nights. It feels like my soft six hundred count sheets are sandpaper on my legs. Any other night, it feels like I am surrounded by cotton clouds. I knew this was coming, so why am I surprised once again? I spent the day up on my feet and was incredibly busy, plus my monthly burosumab injection is just a week or so away.
It’s a RLS night. I shift to my right side, adjust a pillow or two and wait to see if this might help. I reluctantly roll over to my back and then my left side as I quietly pray for this urge to move my legs might go away. I give it one more go, and no relief. Plus, all my moving around had stirred my sleeping husband. I despise his restful slumber.
I finally give in and push the blankets off of me, and feel for my pink house shoes on the floor. I know walking to get a muscle relaxer from the bathroom medicine cabinet will be my best bet, but all I want to do is just go to sleep and stay asleep.
RLS seems to sneak up upon me when my next dose of burosomab is within a week or so away (when my blood phosphorus levels are at their lowest), and I have been extra active the day before. RLS was a more frequent nightly visitor when I first started burosumab treatment versus now when my body is in a phosphorus valley.
The best thing I have found to do is to just get up and move for a bit. I’ve even run a hot bath in the middle of the night to hopefully relax my muscles enough to allow sleep to happen.
I haven’t heard many other patients talk about RLS, so I’d love to hear from you if you’ve experienced it, whether you had it before starting burosumab and if so, whether it’s the same or more/less frequent on treatment, and whether you have any tricks for coping with it.
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Please note that the author is a well-read patient, not a doctor, and is not offering medical or legal advice.
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