TORONTO -- Rockers Billy Talent aren't just a band, they're practically a family. After more than two decades together, the musicians are trying to find a way forward as drummer Aaron Solowoniuk faces a new stage in his fight with multiple sclerosis.

Last year, Solowoniuk's longtime battle with MS took a turn, as the disease hit his body harder than it ever had before. Just as the band was making preparations for their fifth album, "Afraid of Heights," it suddenly became clear his physical condition was worsening.

"I pushed myself too hard trying to get ready," the musician recalls.

"I would play drums and say to the guys: 'My eyes are blurry. I can't really see anything."'

It was the first time since he was diagnosed with MS in 1997 that Solowoniuk faced the possibility that he might have to stop playing drums for the Toronto band.

Sitting inside their studio and rehearsal space, the four original members of Billy Talent recall feeling a shift in his energy. For years, they'd practically taken for granted that his MS didn't show many symptoms, and pushed ahead with their careers.

"We'd have a cooler or refrigerator holding his medicine in the van as we toured," says guitarist Ian D'Sa, recalling when hits like "Try Honesty" and "River Below" helped Billy Talent emerge as one of Canada's most prominent young rock bands of the mid-2000s.

While Solowoniuk would occasionally use his platform to draw attention to MS fundraising efforts, the focus was mostly on making music. As bassist Jonathan Gallant puts it: "Mostly we just tried to carry on."

Staying the course became more difficult when Solowoniuk pulled his back last summer. The prospect of pounding a drum set for weeks was nearly unfathomable as doctors urged him to rest.

He took that message back to his bandmates.

"The first thing they said was, 'We'll wait for you,"' he remembers.

"But I just didn't want to have that over my head because I don't really know how long it's going to take for me to get back."

Lead singer Ben Kowalewicz says he struggled with Solowoniuk's wishes that Billy Talent soldier on with recording the new album. After all, he says, the band stood united through their high school years and now into their early forties.

"We collectively had to make the decision to move forward," Kowalewicz says. "That was the hardest decision, because morally and ethically it didn't feel right."

He likens it to leaving a partner after 23 years and starting anew with a different person. The band agreed they didn't want to make that sort of radical leap, so they reached out to someone they could trust as a temporary substitute.

Longtime friend and Alexisonfire drummer Jordan Hastings was recruited to fill in, and he was confident that sharing past tours with Billy Talent gave him enough familiarity with their music.

"It was weird," Kowalewicz says about putting Hastings in the hot seat.

"But it was the best case of a really (crappy) scenario. We tried to make it as normal as possible."

"Afraid of Heights" sounds like a crossroads between Billy Talent's youthful self-titled debut and an album written by men with perspective on life. The lyrics address topical issues like mass shootings ("Big Red Gun") and the environmental impact of global warming ("Ghost Ship Of Cannibal Rats").

The album recently debuted at the top of the Canadian Nielsen Soundscan Top Albums sales chart, according the band's record label, and bumped aside Drake for No. 1 on the Billboard Canadian Albums consumption chart, which tracks sales and streaming.

Since most of the songs were penned before Solowoniuk was sidelined, his battle doesn't get much acknowledgment on the album. "February Winds" -- a track envisioned after Hastings took over drums -- is the only song to have some foundation in the more recent challenges, the band says.

Solowoniuk wants to support his bandmates whenever he's physically able -- he was out to watch them open for Guns N' Roses in Toronto last month -- but isn't tagging along for the band's tour through Europe.

"I have to decide if it's better for me to hop on airplanes and sleep in hotel rooms," he says, "or if maybe I should ... work on getting better so I can actually perform."

Asked whether he's considered the possibility he may never return to the drums, he sighs.

"I dunno man, I'm just blessed to be able to focus on my health and getting better and getting back out," he says.

"If I can't, then I can't, but I have to at least try."