Platysmal Band injections and an extremely sore throat, is there a connection?

This is most likely coincidental.
The platysma muscle is so superficial.  If The toxin was injected too deep you would not have a sore throat, but just difficulty in swallowing.
Go see your PCP or GP and let them have a look.
You may just have coincidental pharyngitis/ tonsillitis.

Hi,The platysma muscle is located very superficially, just under the skin of the neck, its job is to weakly lower the jaw and pulls the skin around the jaw and corners of the mouth down. It does not have a function in swallowing, the muscles that pull the swallowing apparatus up and down are located much deeper than the platysma. The only explanation I can think of is that the dysport was injected too deep or in a muscle that was not the platysma. Also, dysport can spread (more than botox) and so there is a chance that it was injected in the right spot and just spread to the deeper muscles. It may be worth while returning to your provider and having them evaluate you.All the best,Mehdi Sina, MD

Hello:  
I am sorry that you are not feeling well, however as an Ear, Nose and Throat Specialist I am confident that the Dysport would not have caused such a severe sore throat. Its action is to weaken muscles and if it were injected too deeply, there would be trouble swallowing (not pain on swallowing), which would not have started this soon at any rate. The platysma muscle has no role in swallowing and if there had been trauma with the injection, a large (not little) amount of bruising would be apparent and even with this, it would be sore to the touch and on neck movement but not really on swallowing. 
Please see your physician or PCP for a diagnosis and symptom management  and I hope you get better soon!
Dr. Amanda Maloney, FRCS(C)

Severe sore throats after botox injection is likely a coincidence with the injections, although after practicing for over twenty years I have come to the conclusion that anything is possible. 
Good luck.

If the platysmal bands were properly injected you should see the result within approximately 5 to 7 days. Normally you should not see flu-like symptoms after a treatment using Botox, but there have been reports of people having weak swallowing after the treatment using Botox elsewhere on the face and body. This is a rare occurrence but it has been reported. Good luck from New York City

Hi
Usually for flu virus takes 72 hours to start symptoms but botox takes 7-10 days to work.
But botox migh cause swallowing difficulty.
Thank you
Ramtin Massoudi, MD