The onset of progressive MS was rare for someone of Brownstein's age; it typically occurs earlier. Yet there it was, gripping an upbeat, active, independent man at the peak of his productivity. It would be a total life-changer - if he allowed it to be.
"I remember telling myself, even when I was newly diagnosed, that uncertainty is the norm, and it challenges us to live well in the meantime," he says. "I was not going to cave in to despair or anger, or even a diminished life."
Brownstein - call him "Jersey" - sits in the garden of his Blue Bell home on a recent day, reflecting on the last 21 years. MS's impact has reached beyond him to family and friends, whose love has been worth literally a million bucks.
On Saturday and Sunday, for the 14th consecutive year, they will pedal for Jersey in the annual Bike MS: City to Shore Ride. An expected 7,000 cyclists representing the Greater Delaware Valley Chapter of the National Multiple Sclerosis Society will set out in Cherry Hill on the 150-mile round trip.
Since joining the bike-a-thon, "Jersey's Team" has raised more than $1 million in donations from individuals, not corporations, and for that earned the Larry Kane Chairman Cup last year. (The broadcast journalist, whose mother had MS, organized the event 33 years ago.)
This weekend, more than 100 entrants will be riding in Jersey's name, chasing a goal of $100,000.
As always, Brownstein will be waiting at the finish line, where they make sure to arrive en masse.
"I look at that sea of riders in their bright orange and yellow T-shirts, some of them holding hands, and I feel such gratitude and such joy," he says. "It is the most humbling moment for me, and the most triumphant."
Jersey Brownstein offers what sounds like a bromide, but is in fact a fight song: "Pain is inevitable. Suffering is a choice."
The disease's advance has been steady, the pain chronic, the damage to his body incrementally worse; hence the name "primary progressive multiple sclerosis." It has been resistant to drugs that have sometimes been effective for the more common "relapsing-remitting" MS.
At first, Brownstein needed a cane to walk, then a two-pronged cane. He now relies on a walker, and for longer distances, a motorized scooter.
Simple tasks like brushing his teeth are daunting.
Twice a week, he works with a physical therapist on his mobility. Sensitive to weather extremes, he has found it helpful to swim in an indoor, temperature-controlled pool with a lift to ease him in and out of the water.
"You do what you have to do, and for me, that means moving forward," says a man who, once a hoops star at Haverford High, has coached a granddaughter's basketball team from his scooter.
He has yet to retire. He works full-time, usually at the office, sometimes from home, as chief operating officer of the company his father founded, DSC Steel in Conshohocken, an international distributor of steel and scrap steel. One of his three children, Lisa Goldenberg, 50, is president.
His long career has taken him to the United Nations Office at Geneva for the State Department. At 36, he became the youngest president of the national trade group the Association of Steel Distributors, and represented the industry in the Organisation for Economic Cooperation and Development.
He still travels, though far less. Just checking in at the airport, with his scooter, takes three hours.
Even socializing - he is an attractive, outgoing man - isn't easy. "Dad's visits with friends are limited to my parents' home, or with those who have homes equipped for handicap-access - few and far between," daughter Lisa says. "But my father accepts that. There is frustration, but not anger."
His wife, the former Lynne Finkelstein, an event planner and floral designer, is reading from the same book of life. "Together, we've just taken a different path from the one we expected," she says. "I've learned that, as my husband says, change is inevitable."
But so much of it? Unrelated pancreatic surgery 11 years ago left him with diabetes. Another change, another adaptation.
What Brownstein has learned, he shares with newly diagnosed patients, as well as friends who seek his counsel. "What I often hear is, 'If you could deal with this, you can guide me,' " he says.
His example also has impelled his family onto paths they couldn't have imagined two decades ago.
Daughter Andrea Rosenthal, 45, has captained "Jersey's Team" for the last 12 years, along with organizing the preride pep rally at the Brownstein home and finding overnight accommodations for bikers.
Son Larry, 48, has served on the board of directors of the local chapter of the National Multiple Sclerosis Society.
By being at his side day after day, Lisa enables her father to stay at the helm of his company.
Brownstein's message, about the rewards of his unexpected journey, has gotten through to his six grandchildren as well.
At 14, Rachel Rosenthal observes, "For my grandfather, having multiple sclerosis is just the way it is.
"He teaches us to live our lives, and be grateful."
For information on the Bike MS: City to Shore Ride for the Greater Delaware Valley Chapter of the National Multiple Sclerosis Society, visit www.mscycling.org or call 1-800-445-2453.