These two are very different terms in medical language. Both imply muscle “spasm” or involuntary contraction; however, both are caused not by muscle disorders, but by brain or spinal cord disorders. Any of us might experience a muscle spasm as say in a muscle cramp or after any painful injury muscles may tighten up. These are muscle spasms, but not dystonia or spasticity.
A source of confusion is an old term for torticollis “spastic torticollis.” However, both words are not specific for dystonia that is why current medical terminology labels ST “cervical dystonia” rather than spasmodic torticollis. Spasticity is a tightening of muscles that selectively involve muscles of the upper or the lower limb. The characteristic posture that a stroke victim has in the arm or leg comes from the unequal involvement of those limb muscles. The tightness of the joints in those limbs may be aggravated with attempted use, but not as much as its characteristic in ST. As you STers know, if you try to initiate a neck movement may increase the dystonic muscle spasm, so that the movement may be impossible.
Botulinum toxin can be used to treat both dystonic spasm and spasticity; however, the muscles injected in spasticity are those selectively involved in that process. That pattern is similar from person to person. In cervical dystonia, the pattern of muscle involvement is variable, which is why EMG mapping of the dystonic activity helps to determine, which muscles and with how much each muscle should be injected.
Torticollis sufferers of course can have strokes or other disorders that produce spasticity, but from dystonic disorders, the development of spasticity should not be a feature. I hope this helps clarify the confusion.
Drake D. Duane, MS MD
Director Arizona Dystonia Institute, Scottsdale, AZ