Portnoy, who co-founded the progressive metal veterans with guitarist John Petrucci and bassist John Myung in 1985, returned to Dream Theater following a 13-year absence in October.
LaBrie, 60, recently responded to the return and the subsequent fan response on Instagram.
“Wow, what can I say, I’ve been pretty silent and overwhelmed with the reaction…” he wrote.
The singer then teased that the band are planning work on a new studio album and world tour.
“Thank you so much for the incredible response to the reunion of Dream Theater’s classic line up. We are beyond grateful and excited to begin the next chapter with a new album and world tour. Gonna be one hell of ride for all. Welcome home, my friend.”
Portnoy’s return to Dream Theater was announced on October 25. The drummer is replacing Mike Mangini, who joined the band as Portnoy’s replacement in 2010.
“I am overwhelmed with joy to be returning home and reuniting with my brothers!” Portnoy, 56, said in a statement. “There is so much shared history between us all… so many memories, so much music… to think we’re coming up on 40 years since this journey began!
“The idea of creating new music together is so exciting and I absolutely cannot wait to hit the road and get to play live for a whole new generation of fans that weren’t ever able to see this line-up before… There’s no place like home!”
Mangini, 60, also commented on Portnoy’s return.
“I understand Dream Theater’s decision to get Mike Portnoy back at this time,” the drummer said. “As was said from day one, my place was not to fill all the roles that Mike held in the band. I was to play the drums in order to help the band carry on.
“My main role of keeping our live show working tightly on a nightly basis was an intense and rewarding experience. Thankfully, I got to experience playing music with these iconic musicians, as well as some fun times laced with humour. I also really enjoyed spending lots of time with the crew.
“And then there’s the Grammy win, which was amazingly satisfying. To the fans: thank you so much for being amazing to me. I cherish the pictures I have of you all losing your minds and having fun. Finally, I really love the band, crew, and management and wish them and the entire organisation all the best.”
Mangini’s debut solo album, Invisible Signs, came out this month.