Multiple sclerosis charities have said they are "bitterly disappointed" at a decision not to prescribe an anti-MS drug in Scotland.
MS affects the body's central nervous system
Both the MS Society and the MS Trust believe the drug Tysabri could help slow the progression of disability in hundreds of sufferers.
But the Scottish Medicines Consortium said the economic case for the drug had not been demonstrated.
The charities urged sufferers to fight for Tysabri on an individual basis.
The MS Trust claimed that about 1,000 people with the disease could benefit from the drug.
Chief executive Chris Jones said: "We share the sadness of Scots with MS at this decision, particularly those for whom Tysabri offered their only chance of holding back this cruel disease.
"Clinicians will be prevented from prescribing an effective licensed treatment to people in need."
SMC decisions are based on cost-effectiveness, using the cost per quality adjusted life year (QALY), which tries to determine the value of a treatment to a person's life, rather than the actual cost of providing the drug.
"Accountancy has trumped clinical evidence with this decision," Mr Jones added.
"For a well-defined group of people with MS, where the disease is running out of control, this drug is highly effective, leading to 60-70% reductions in relapses. Only an economist could make that sound expensive."
The MS Society Scotland, said Tysabri was the only drug licensed for MS that had shown "significant promise" in slowing the progression of disability.
Director Mark Hazelwood said the society was bitterly disappointed.
He said: "This means people with the most aggressive form of relapsing remitting MS now have little or no option.
"No other drug has shown this potential to reduce disability, and any short-term savings are likely to be outpaced by the devastating financial costs of living with severe, progressive disability - not to mention the emotional costs to people with MS and their friends and families."
Tysabri had been welcomed as an important breakthrough and compared with current treatments had shown an impressive reduction in relapse rates and a significant reduction in the risk of disability progression.
While people with MS in Scotland can still be prescribed Tysabri their health boards would have to override the SMC's advice to pay for it, which is very rare.
The only alternative would be for people with MS to find the money themselves.
Mr Hazelwood added: "The SMC offers no option for appeal, but we are ready to work with people with MS on a case-by-case basis to put pressure on the NHS.
"Tysabri is already being prescribed in Ireland, Germany and the USA. But here in Scotland, with the highest rate of MS in the world, it is effectively off the menu."
Mr Hazelwood said the society would be contacting the health minister over the issue.
Dr Gavin Giovannoni, of the National Hospital for Neurology and Neurosurgery in London, this year described the drug as the most significant advance in MS treatment in nearly a decade.
A spokesman for the SMC said: "At this time we are not able to recommend it for use in the NHS.
"The drug company can always make another submission."