Over Tuesday and Wednesday of last week, the Food and Drug Administration (FDA) advisory committee held a long-awaited meeting that has all but secured the comeback of the Tysabri multiple sclerosis treatment, touted as a wonder drug when it first hit the market.

All looked promising until a usually fatal rare brain disease, progressive multifocal leukoencephalopathy (PML), was found in three patients taking Tysabri in combination with other treatments.

Two of them died, hammering Elan's stock and that of its joint venture partner, Bostonbased Biogen-Idec.

It had all happened before.

A previous accounting scandal had given Elan shareholders a taste of financial destruction and of redemption. Massive profits were made by those brave enough to buy the stock when it slumped below $2 back in 2002, reaping huge returns when a restructured and resurgent Elan, riding on the back of so far positive Tysabri trials, saw its share price hit $29 in January last year.

The party would abruptly end as news of the PML-related deaths emerged at the end of February 2005. That saw many investors scrambling to cover positions that ultimately resulted in some of them being almost wiped out financially. Hard lessons, but even then a new raft of investors was poised to bet on the ailing stock.

Last week, after some nervous jitters previously as a result of negative news flow, those who snapped up the shares at prices below 2.50 could finally breathe a big sigh of relief, as could MS patients who had found Tysabri to be the wonder drug as which it had been hailed. Many now have a chance of resuming treatment, probably within a couple of months. The FDA will make its ruling on the panel's findings at the end of the month.

Investors had already got a pleasant surprise last week when the advisory committee recommended, albeit by a tight vote, that the drug be made available to anyone with relapsing or remitting MS, and that Tysabri should also be available as a frontline therapy.

Availability of Tysabri as a 'frontline therapy' would give doctors the option to prescribe the drug as a first resort rather than a second.

Should that recommendation be accepted by the FDA mandarins, it places Tysabri in a considerably stronger position.

The fact that there will be more stringent controls over the administering of the drug, and increased and compulsory monitoring of patients taking Tysabri, is likely to dampen demand somewhat.

But it has been as good an outcome as could have been expected.

"It really was as good as could have been hoped for, " agreed analyst Ian Hunter of Goodbody Stockbrokers, who was present at the two-day hearing. "It's a better stock now with slightly less risk, but there's also less upside on it. The Americans are still wary about it. They're putting up their forecasts now, but not to the same numbers as the Europeans."

In Dublin, the day after the hearing ended, Elan rose as high as 14.25, compared to 11.30 on Tuesday, before giving up some of those gains later in the day. In the US, the stock jumped from $12.70 before the panel meeting to over $15.

While Tysabri's return to market is fortunate for Elan, it also serves as a constant reminder of what could have been. It had been hoped that Tysabri would generate annual sales of over $3bn at its peak. Now those sales are expected to reach varying estimates of between roughly $1.2bn a year, according to Piper Jaffray, and as much as $1.9bn, according to Goodbody Stockbrokers.

The consolation: it could have been nil. Other brokerages are also exercising caution, with Deutsche Bank also projecting peak annual Tysabri sales of $1.25bn. But to all intents and purposes, Elan looks like being back on track.

What investors can begin focusing on now is Elan's Alzheimer's treatment, AAB001, developed in conjunction with Wyeth, which is showing promising results as it negotiates its way through patient trials. No side-effects have yet been reported. Goodbody Stockbrokers reckons the drug could be on the market by early next year, which could give a further fillip to the stock.

Meanwhile, the return of Tysabri will bring mixed feelings for some MS sufferers. One female MS patient in Indiana was given an Avonex treatment, directly followed by a Tysabri infusion, on the same day early last year. She was also taking steroids.

Her condition worsened rapidly and her neurologist wanted her to have a spinal tap to determine whether she has contracted PML, but she is unwilling to be subjected to the test. While there are concerns she may indeed have contracted the condition, it seems likely that her family and doctors will now have to wait until an autopsy can reveal any signs of PML.

Two of the three patients with confirmed PML had been taking a combination of Avonex and Tysabri for over two years. A relative of one of them last week welcomed the fact that there would be more information available on Tysabri and that patients would be closely monitored, and that the panel has advised, as was expected, that Tysabri be used as a monotherapy only.

Others who used Tysabri successfully before its withdrawal now face an uncertain future. Toronto native Wendy Sargent's condition improved substantially while she used the treatment for about three years. Since it was withdrawn, Sargent has developed antibodies to the drug and will be unable to take it again. Between 4% and 6% of patients taking Tysabri are likely to develop such a reaction. Sargent said last week that she remains "thankful" for the time she spent on the drug.

For many patients, as well as investors, it seems there is finally some light at the end of what has been a very long tunnel.