Published: Apr. 17, 2025, 3:05 p.m.

In season 1 of “The Last of Us,” Frank (Murray Bartlett) battled a degenerative disease that affected his mobility. But what exactly was his diagnosis?

Neither Frank nor his romantic partner/caretaker, Bill (Nick Offerman), mentioned his illness by name during season 1, and that was by design.

MS stands for multiple sclerosis, an autoimmune disease that damages the insulating covers of nerve cells in the brain and spinal cord. Like Frank in “The Last of Us,” people with MS can become wheelchair-bound and experience muscle stiffness and tremors.

ALS, also known as Lou Gehrig’s Disease, stands for amyotrophic lateral sclerosis. Unlike MS, it is considered a terminal illness. The symptoms include trouble walking, hand weakness, and muscle cramps and twitching. ALS is a progressive disease, meaning that symptoms worsen over time.

Warning: Spoilers ahead for season 1 of “The Last of Us.”

As if living with a chronic illness weren’t challenging enough, Frank’s symptoms began after an outbreak of a fungal infection that turns humans into zombie-like creatures. His disease was unrelated to the pandemic.

In episode 3 of “The Last of Us” season 1, Frank, who lives with Bill in a fortified home cut off from the rest of the world, decides that he’s ready to die.

“What if somebody shows up who can help?” Bill asks.