Can thoracic outlet syndrome be mistaken for early-onset generalized/post-traumatic secondary dystonia or visa versa?

Unlikely.: TOS usually has weakness or pain associated with particular arm movements. Dystonia is usually an abnormal and or erratic arm or leg movement with excessive tone at times. Increased muscle tone is seldom seen with TOS (thoracic outlet syndrome).

Yes: They are both seperate and distinguishable clinical entities, but both are often characterized by initial delays and inaccuracy in the correct diagnosis. Never hesitate to get a second opinion.

Can happen: Have seen multiple mis-diagnoses regarding TOS challenges, and seems to be tough to nail down in many locales. If EMG specifically studies brachial plexus, the diagnosis can be apparent. To sort this out, may need to see a vascular surgeon.