The stroke that tore through Paul West's brain was, says his wife, "tailor-made to his own private hell". Both are acclaimed writers. Paul is a novelist, critic and lecturer; his wife, Diane Ackerman, is a poet and naturalist. Between them, they have written about 70 books. Her husband, as Diane notes in her beautifully written memoir, One Hundred Names for Love, had one of the largest English vocabularies on earth and "a draper's touch for the unfolding fabric of a sentence, and he collected words like rare buttons".

Theirs was a relationship steeped in language. They had met in the early 1970s at Pennsylvania State University – he was the eccentric and brilliant British professor, and Diane, the 18-years-younger student. On their first date, Diane went for drinks at Paul's house, they talked until dawn and she never left; they have been together for 41 years. Perhaps because they never had children, they both seem markedly childlike, despite their towering intellects. He liked to roam around the house naked, like a toddler who refuses to wear clothes, and adored nursery food from his English childhood. They would invent silly word games, songs and outlandish pet names for each other, and loved puns.

Then in 2003, in a hospital room in Ithaca, upstate New York, where Paul had been admitted three weeks earlier with a kidney infection, came the stroke. It ravaged the key language areas of his brain, leaving Paul with aphasia, or loss of language; the words, as Diane would later find out, were still in there somewhere, but the sorting processes – the links and moorings – were gone. When he came round, all he could say over and over again was a single nonsense syllable, "mem". This from a man familiar with words such as animadversions and atrabiliousness.

"I thought it was the end of our world," says Diane. "I didn't know how I would cope. It took quite a while to accept that nothing was going to be the same again."

She points out that ironically she was one of the best – and worst – people to deal with the stroke because she had just finished researching and writing a book on the brain, An Alchemy of Mind. "The CT scan of his brain looked like it belonged to a man in a vegetative state," she says. "I knew in chilling detail what had happened and that you don't recover from that kind of stroke, you only improve. I was lucky to have that knowledge of the brain, but as a wife it brought considerable terror. But I knew that brains are not immutable – they are plastic and in a nutshell that meant don't ever give up hope."

Numbers and symbols now meant nothing to Paul. He had also lost his procedural memory, the ingrained knowledge of muscle movement and coordination that enables us to brush our hair or get up after falling.

A long period of speech therapy and physical rehabilitation began. "I decided early on that I would not be his assistant," says Diane. "It was important for me to be his wife, not his healthcare aide, although I did a lot of that too." In her book, Diane writes of the terror of the loss of her own independence: "I feared I was either going to have to give up my career and just take care of Paul, or feel like a total monster and have my career but not take care of Paul … finally, I learned to embrace it as a whole."

Paul has Liz, his assistant, whom they met when she was a student nurse at the hospital. "Part of my life is an author, part caregiver," says Diane. "But my life still includes this wonderful person who has been my soulmate for a long time. For me, early on, the question was how to make the most of the situation that we were now in. We had always been playful and romantic, and the challenge was to keep our love story alive. In time we did, but it wasn't easy – it took a lot of creative thinking and determination not to give up."

Paul needed a lot of care. He couldn't be left alone for long in case he fell, which might have brought on another stroke. His lack of comprehension meant he couldn't be responsible for taking his own drugs. He also had to be supervised at mealtimes to make sure he didn't inhale his food, which would have created a risk of pneumonia.

One day, early on in hospital, Paul managed to tell Diane that he wished he were dead. "I knew he was serious at the time, and it's really important to take people seriously when they talk like that," she says.

"I would tell him, 'Look, that's always a possibility and an option, and I'm not going to talk you out of it, but let's talk about other options.' It helped to focus on each success in his recovery, making sure he was surrounded with people who had a positive outlook, and were caring and encouraging. "It helped when I explained what had happened and that he could improve, and that I loved him and wasn't going to leave him. I told him I was sorry that he had to go through this, but that we were going to survive it."

The stroke wrought such dramatic changes. Did Paul still seem like her husband? "Yes, he did. It's important to remember that after you've been together for many years you're not the same people – you've been in several marriages by that point because people change.

"I still love what is most lovable in him – he is smart, he is funny. There are things I miss, like having normal conversations in the way we used to, so I have those with friends more often. But I suppose I knew years ago that if you marry someone who is nearly 20 years older, there may be a time when it's going to be a problem."

One of the things Paul missed most, says Diane, were the hundreds of pet names he had created for her – "I was a one-woman zoo," she says. He couldn't remember them so Diane encouraged him to create new ones – the "hundred names" in the title of her book – to create a linking thread to their life before the stroke and also as a more entertaining way to practise language than his speech-therapy sessions.

One advantage of the aphasia was that Paul could produce wildly creative snippets of language, because there were no rules any more. Diane's favourite new pet names include Spy Elf of the Morning Hallelujahs and Parakeet of the Lissom Star. She laughs. "I don't know where they came from, but they're wonderful. Even though Paul had trouble finding the words he had learned when he was little, he had retained the big words he had learned as a grownup. He would come out of the bedroom and say 'Where's my cantilever of light?' I suppose you can only know that this means a velour tracksuit when you have been living with someone for four decades."

Diane discovered, other unexpected benefits. "Our relationship changed for the better in some ways," she says. Before, his loving side was balanced with volatility, and for years, Diane writes, "I'd walked on eggshells around him, because it took so little to trigger what he described as his 'Irish temper' … [the stroke] produced a sweeter, less stormy Paul, which I found wonderfully welcome."

Now, she says, "he's more supportive, he's so grateful to be alive and he lives more in the present. If anything, I think he's happier than he was before." Can this really be true? "I think so," she says. "There are many reasons, but the primary one is the great appreciation for life, and that each day is a gift. For the beauty that is out there that perhaps he didn't make that much time in his life to notice. I think he also has fewer professional expectations. People assume that because he's had a stroke he's not writing anything, so there isn't that pressure on him, even though he is writing and publishing."

Two years after his stroke, Paul started writing in longhand again, helped and encouraged by Diane in daily sessions. Now he writes daily and Liz types up his words before he corrects them – a system that is repeated again and again until he is happy; since the stroke, Paul has written three novels, a memoir on living with aphasia, as well as essays and book reviews. "It shows what can be done when you have hope and determination," she says.

The house is dotted with bits of shocking-pink tape, on the buttons of the microwave and the television remote control, for example, so Paul knows which ones to push. "I designed shortcuts to let Paul be as independent as he could be," says Diane. "That was also positive for me because it helped retain the sense of living with an independent partner."

As Diane wrote One Hundred Names for Love, she would read the pages to her husband over dinner. "At the time of his stroke, his brain was too injured to make memories, so he was enormously surprised because he remembered none of the details," she says. It also helped her to come to terms with her altered husband and to replace, with some kind of acceptance, the panic of those early days after the stroke.

"If we remember that life never stays the same," she says, "I think it's a lot easier to accept change. I regard it as part of the extraordinary adventure of being alive, that involves tragedy and joy. Even if Paul and I can't go back to how it was, which I think of as a kind of magical land, life is very sweet."

One Hundred Names for Love by Diane Ackerman is published by Norton, £16.99. To order a copy for £13.59 with free UK p&p, go to theguardian.com/bookshop or call 0330 333 6846