When, many years ago, the great Leon Fleisher played Ravel's Concerto for Left Hand at the Edinburgh Festival with Andre Previn as conductor, I recall rebuking him for resting his right hand on top of the piano - an artistic pose, as I wrote at the time, that had been denied Paul Wittgenstein, the work's dedicatee, who had lost his right arm in the First World War.

The following day I myself was rightly rebuked by the pianist's agents. Did I not know that Fleisher was disabled, and could no longer play with both hands? The tragic truth had somehow eluded me, as it had also the critic of The Guardian, who reviewed the performance in similar terms. Today, nearly 40 years later, things have changed.

Fleisher has conquered the neurological malady known as focal dystonia, from which he was suffering and which had impaired two of his fingers, causing them involuntarily, and painfully, to curl over.

But at the age of 80, thanks to a series of botox injections, he is again performing as normal, and at last month's Lucerne Piano Festival, where he appeared alongside Alfred Brendel, Pierre-Laurent Aimard, Jean-Yves Thibaudet and other keyboard masters of the day, the sound was wonderful to hear.

Fleisher, born in San Francisco and for 10 years a pupil of the peerless Artur Schnabel, is a big grizzled bear of a man who does not conceal his delight at being able to play again the two-handed music he adores, though his repertoire still includes - for old time's sake? - Brahms's little-known left-handed arrangement of Bach's D minor Chaconne for solo violin, one of the works that sustained him when his other hand was refusing to function. Seated at the keyboard he now looks rather professorial, with the music in front of him and a page-turner at his side. Indeed, during his one-handed period, much of his time was devoted to teaching and giving famously humorous masterclasses, bristling with spirited metaphors as he steered potential pianists through Schubert's sonatas.

In Lucerne's lovely concert hall, its gleaming white interior a triumph of modern architecture, Brahms's Bach transcription formed the centrepiece of Fleisher's recital.

It was an austere, grandly sonorous and (at the point where the harmony moves hauntingly into D major) very moving performance, during which he permitted himself once again to place his right hand, briefly - and on this occasion quite touchingly - on top of the piano.

Earlier, having opened his programme with Egon Petri's gentle, wispy, two-handed arrangement of Sheep May Safely Graze, sweetly textured and filled with what sounded like distantly murmuring oboes, he progressed to the great Chromatic Fantasy and Fugue with enthralling control and keen two-handed delineation.

Later came Debussy, Albeniz and Chopin, all boldly unfurled, right hand fascinatingly matching left hand in illuminating the chords of Debussy's Submerged Cathedral, the subtle Spanishry of Albeniz's Iberia, the rhythmic finesse of a Chopin mazurka and the rolling thunder of the C sharp minor Scherzo. The fact that this was an octogenarian's Chopin was not inaudible in Fleisher's fingerwork, but it was shot through with an octogenarian's mature perception of the music.

For an hour the previous evening, Fleisher had talked to me in his grand lakeside hotel - from where, during the summer, people can boat to the concert hall on the opposite shore - about how he had spent his disabled years, and about the five-fingered performances upon which his dystonia had forced him to concentrate. He was not, as he pointed out, alone in this malfunction. As he put it: "It's task specific. Glassblowers get it. Computer workers get it. Golfers get it, and begin to miss their putts." Ravel's left-handed concerto was, of course, a godsend (Wittgenstein's approval of the work had always been grudging because he considered it to be overscored), yet it was not the only fine music at Fleisher's disposal.

Prokofiev's scintillating Fourth Piano Concerto (likewise written for Wittgenstein and despised by him) was also available, as was Korngold's romantic left-handed concerto. Richard Strauss and Benjamin Britten provided further options. Moreover, as he discovered, there were at least a thousand solo pieces for left hand, "mostly pretty bad". Sifting through them, he managed to gather about "two programmes' worth" of interesting music, including a sonatina by Dinu Lipatti, that unsurpassably poetic pianist, much loved in Lucerne, who had died in 1950 at the age of 33.

That was something, as Fleisher recognised, far worse than losing the use of a hand. But through conducting and teaching, and through the recent discovery of an unknown Hindemith concerto which the ill-humoured Wittgenstein had commissioned but disdained to play, Fleisher triumphed over infirmity.

Discovered after every drawer and closet in Hindemith's widow's apartment had been searched, it was not the same as having Mozart's 18 greatest piano concertos, the five Beethovens, the two by Brahms at his disposal, but it was certainly better than nothing. By then, in any case, Fleisher was well on the way to full recovery. But the premiere of the work was his for the asking and, with Simon Rattle and the Berlin Philharmonic, he performed it five years ago, deeming it to be well worth promoting as the product of a currently unfashionable composer caught here at the height of his powers.

While Fleisher's has been a process of belated musical reincarnation, Brendel's, at the age of 77, is now a matter of planned withdrawal from the concert platform. His farewell to Lucerne was much the same as his recent farewells to Edinburgh and Glasgow, but he was now closer to his final destination - Vienna - where, playing Mozart's "Jeunehomme" concerto, K271, with the Vienna Philharmonic and Sir Charles Mackerras, he was due this month to sign off from a career of the highest distinction.

In Switzerland, as in Scotland, it was with Schubert's last and longest sonata (though as always he persisted in shortening it by omitting the first movement's exposition repeat) that he said adieu. If his playing sounded even more responsive than in August at the Usher Hall, this was perhaps simply because the Swiss audience behaved better, and did less to irritate him, than Edinburgh's. At any rate he rewarded his listeners with the most apt of encores - Liszt's study of Lake Walenstadt, from the Swiss volume of the Annees de Pelerinage, leading to one of Brendel's beloved bits of Bach, the Busoni arrangement of the chorale prelude Nun komm der Heiden Heiland.

Lucerne's Piano Festival in its 10th year is younger than the more famous summer one, which has Claudio Abbado and Pierre Boulez as its current figureheads but goes back to 1938 and the Toscanini era. The Easter Festival, another recent development, will celebrate the Haydn bicentenary in 2009.

Despite what may seem its unashamed elitism - it all resembles Edinburgh as it used to be - Lucerne's eye for fresh talent landed this year on Martin Helmchen, a willowy young Berliner whose account of Symphonic Studies provided the deepest pleasure.

A new opera house, to complement the success of the marvellous concert hall, is in the offing. It will be worth waiting for.