Wow very interesting. Truly there are a lot of different versions of EM and it sounds like this is one type of it from what you have said.
A couple thoughts. Getting excited and stressed can often trigger it. Perhaps with a "minor form" of it a person isn't always triggered when they are excited but blood pressure being elevated could bring it on. Gotta wonder if when she is excited if the distraction causes her to ignore symptoms when she is distracted enough by something she likes or if her hands swell each time she gets a flare and it's noticable.
The heat and temperature of the skin being different are interesting as well, sounds like classical EM there.
I can't speak for everyone or even a small sample of EM patients, know basically what I've read out there and what I've seen with our own strange case here. I'm wondering in some cases if this could be triggered as a secondary flare from the arthritis, it seems to me that that can at times trigger EM as well. Which might in your case not show any nerve type of damage that could be discovered.
There is obviously a lot of guess work on my end as a layman, so it's often better to go with the doctors.
I can't say how she'd react to various nerve tests, but I can say that my mom had nerve velocity tests by a neurologist and my mom has some hyper sensitivity to touch and her EM causes her feet to be very sensitive but she almost always has a kind of low level flare. That could be a sign that my mom has a lot of nerve damage compared to some cases. But in the case of my mom, when needles are put in her leg for any kind of test, she later complains about pain where the needles were in, even 8 or more years after she was tested with needles for nerve velocity tests she has at time complained about the pain or sensation from those tests. So my opinion, which can almost be worthless but is just based on our experience is be conservative on the tests involving needles and nerve velocity tests.
Every person is different of course, but perhaps some like my mom are more affected by drugs that pass the brain blood barrier. Those kinds of drugs are sometimes more useful in targeting pain related to nerve conditions, because they can get to the nerves affecting EM. But those drugs could also damage the neurological system perhaps in some way. Perhaps not for most EM patients, but for a subset of them.
The cream helping her sounds interesting some creams help EM patients and finding the right one can benefit. In some cases creams like the one you mentioned may hold in the heat, because they are more greasy than others. We have not had luck with some numbing creams because of heat buildup. Once you find a good cream that works, there is no harm in sticking with it. For my mom creams like Hawaiian Tropic with Aloe will hold in the heat and cause as much pain as relief if not more, because heat retention hurts her, but she probably has a much more severe form of the disease than your daughter. My mom has luck with lanacaine and we often mix it with Camille Backman's french vanella cream. The Lanacaine is available anywhere, and the Camille Backman's cream is found around here at a Hallmark store and one hardware store, although it can be ordered online. We mix 50/50 but at times we have put lanacaine on her foot without the mixture and it works as well or better sometimes without a mixture. The other cream helps moisturize the area of my mom's foot as well so that's what works for her without heat buildup.
I wonder, but this might not matter for flare ups if a lidocaine pain patch would help. I find it interesting that lidocaine type numbing agents can help many patients, maybe that is natural and based on the pure effects of those being able to numb the area a bit, but perhaps it's a sign that they would respond well to other lidocaine based treatments.
If you can afford it, I'm not saying of course you must, but I'd wonder strongly if she has this from the genetic defect. Being so young and having that is a sign that it's from the Nav 1.7 genetic defect. If she had it from that you might have good luck with the Mexiletine treatment, but then again being young perhaps just dealing with flares as they happen could be enough. If she is being treated for arthritis, does she experience flares when that pain happens as well? I wonder how much of this could be possibly a secondary relation to perhaps this other condition. Also have you put her hands in warm water and seen flares result? I'm assuming you have as heat almost always generates a flare.
The Chinese version of EM which was caused by a pox virus affected students who were sleeping in cold conditions in one case. So the cold weather was thought to trigger it in some mysterious way. But I don't know how rare that condition could be and if anyone in the western world has every been found to contain a rare pox virus to cause their EM. One article stated that it was a damage to their autonomic system which is some kind of damage to the nerves that automatically regulate the nerves. I'm also wondering, but this is more of a general question the the group as a whole and might be a better subject for a stand alone topic, if patients who have EM flares experience strange pain in their hands or legs which have flares if the hands or feet are brushed in different ways with a soft brush. I find it interesting that my mom has pain from a soft brush on her feet, and wonder if other EM patients have the same kinds of reactions. Is that a sign of some kind of neurological defect? I'm just wondering as a casual observer of EM symptoms here, not as a medical professional of course. When it doubt, always ask a professional.
In our case of course as with many EM patients we end up asking a lot of questions of different doctors and this of course can be very time consuming for them. So in our better visits we have a list of the more important questions and will ask them. In our meetings with the doctor where mom goes off into other ailments and tangents, sometimes we leave with virtually no new answers to some EM related questions. In our case, but I'm getting off the subject, the habits to avoid pain triggers have caused other health problems, so we end up with secondary problems in mom's health due to the adaptive changes in lifestyle to avoid pain.
In my opinion, but this is just my lay opinion if I had any young person with a confirmed case of EM happening, I'd get the genetic tests. I really want to test my mom as well, but we just haven't done that and people who develop EM late in life often are not tested for it as they are falling out of the pattern of the genetic defect. The best reason to test is to get some kind of other confirmation and because she is so young. We have thought about whether my mom's is some rare form of genetic related primary EM. And we often wonder is her's due to the genetic defect. Some say if the patient is not young or more than one relative doesn't have it, you're better off not testing for it. I wonder however, should I wait for my younger sister to possibly develop it later in life before we get my sister tested? Should we just try an oral lidocaine first? Or should we get the test first? They are really two different questions and supposedly the oral lidocaine can help some, perhaps even those without the genetic version of primary EM. It's more likely that oral lidocaine however will work with a genetic version of the disease.
In either case you can always do the genetic test later. Perhaps her flares will go away over time or treatment for other conditions will help and if it's minor and something you can deal with you an always do the tests later.
KEEP GOOD NOTES
One of the best things you can do is keep a diary of things you've noticed. It can perhaps give a clue. Have it with dates and details that you notice, as long as it doesn't totally consume you're life, you'll find such a diary could be helpful if the disease and problem lasts for years and years.
(If a doctor tells you why one of your theories or questions is wrong, it's a good idea to jot that down fairly soon in a diary as well. I think more notes are better. Doctors will of course offer different opinions and ideas on how to treat a rare disease. They may end up with a list of treatments and options which they will run through over time to see what works and what doesn't. I have to wonder out loud here, does every EM patient respond well to lidocaine creams and numbing creams?) I'd also say beware of steroids for a young one if it ever comes down to that. Although rare, a side effect to steroids could have a major impact on a young person's life. I know of one friend who had steroids when he was ten and it caused major stunting of his growth. He developed a disease/reaction from the steroids. That caused a massive change in his health as it stunted his growth. He stayed at the size of a ten year old. So heavy duty drug treatments can cause heavy duty side effects in rare cases, so be careful with your young ones.
Of course changing one thing at a time, if you're trying to determine what will help is better if one has the chance to do testing of things that can help. If one changes to many things at one time, it could be difficult to determine what helped. As an example my mother had a nerve block but also received a vitamin shot. If she experiences some kind of side effect where did it come from? That may be a bad example. But in the cases of medication of course, most doctors will not load a person up with a lot of new drugs, because they can't tell what interactions are going to happen and which drugs were actually effective. So adjustments in treatment may take time.
And keeping good notes can be valuable. We have had some drugs that didn't work and we noted them down, but others we talked about and we may have discussed them for a while and thought the side effects would remain in our collective memory. Then years later when we are told about a drug from a new doctor which already had bad side effects, due to a lack of organized notes we had to search our memory and wonder the exact side effects that happened with some of the more rare drugs we have tried.
This is also common sense, but it's also a good idea to prioritize the questions you have to the doctor and have a really brief question for each point, so as not to waste their time to much. I've been in appointments where both parents and I could go off on tangent points (kind of like my posts at times. . . ouch) and that wasted to much of the doctors time. I've gone to a neurologist with five to seven questions on a short list and only had three or four of them answered. To prioritize the questions and ask the more important ones is an obvious common sense good idea in preparing for an appointment. Sorry but I'm starting to get a bit off topic.