Answer: Crepe myrtle is at the edge of its winter hardiness zone in your area, and depending on which variety you have planted it might suffer terribly in a bad year. A dry and extra cold or windy ,winter or a dry fall followed by frozen ground, could certainly cause it to dry out, thus making it more susceptible to cold damage. (A very wet winter could also cause it to have too much moisture at the root zone and suffer damage as a consequence of that.)
Usually this type of winter damage (and also drought damage) would cause dieback from the branch tips first, then working its way down the plant. So you would see buds and new growth from older wood and possibly from the ground as well.
If you are seeing new growth at the tips, or have lost the tips but are seeing it midway along the branches, it is possible the plant is beginning to take on some tree-like characteristics as it matures. This would eventually result in a bare trunk with growth at the top.
If you like it in a tree shape, any new growth from the roots could be trimmed off to accentuate the single (or multi-stemmed) form. If you would prefer to have it more bush-like, you can prune back the oldest stems in late winter, cutting them off at the ground. This will stimulate new growth from the base of the plant.
Crepe myrtles bloom on new growth of the season, so either way you should still have blooms this summer.
One other possibility is that there is a rooting problem underground causing the plant to begin to be stunted a bit. This could be the result of poor rooting for whatever reason such as poor planting procedure or a rootbound plant or an underground obstruction or so on.
Since I have not seen the plant it is difficult to really tell what is happening long distance. If you are unsure, I would suggest you work with your professionally trained and certified nurseryman and/or your county extension. They should be able to tell you if crepe myrtles in general in your area had a rough winter and if this is typical of what they are seeing as a result, or else help you troubleshoot if it might be related to something else.
Good luck with your crepe myrtle!
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