I have found that clinically Medical Acupuncture (including Dry Needling) is effective in reducing muscle tone during the rehabilitation phase in those who have suffered from a stroke. It has become an integral part in my approach to treating hemiplegia.
The mechanism is most likely an inhibitory effect at the anterior horn cells when the hypertonic muscles are needled directly. The reason for the hyperactivity at the anterior horn cells, which in turn controls resting muscle tone, may be reduced proximal modulation of the anterior horn cell activity after a stroke, in others words less ‘top down’ control from the brain.
There is also some good anecdotal evidence (no hard evidence yet as far as I am aware) for needling the antagonist muscles i.e. the muscles on the opposite side of the limb to those that are hypertonic. For example needling, usually with electro stimulation, the extensor muscles of the forearm to ‘relax’ the often hypertonic flexor muscles. The mechanism here may be some kind of reciprocal inhibitory effect?
Both approaches must of course be followed up with stretching and mobilising physiotherapy techniques and exercises, as well as facilitation with the intention of improving function.