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In their detailed cost of illness study, Cartonet al estimate the total annual costs in their population of 5500 people with multiple sclerosis to be ECU 13 106 000 (£8.7m) for ambulatory care and ECU 26 581 000 (£17.7m) for hospital and institutional care.1
They conclude, as have others,4 that the costs of multiple sclerosis rise with increasing disability and that the information is useful for cost effectiveness studies.
However, to be useful for such studies, the costs would need further description, in particular we would need to know which costs were fixed, and which were semifixed or non-fixed. In our own institution we know that 40% of the cost of a bed-day is fixed and at most 5% of costs are non-fixed. The remaining costs are semifixed—for example, staff salaries (Robert Hudson, Scottish Health Purchasing Information Centre, personal communication January 1998). The important point is that most of the costs in their paper are probably fixed or semifixed, and interventions to reduce disability are unlikely to have a significant impact on these costs as described. Nevertheless, their data do allow the cost implications of interferon-β for secondary progressive multiple sclerosis to be assessed, albeit given some gross assumptions. If we assume that the effect of treatment with interferon-β lb for secondary progressive multiple sclerosis5 is to delay time to a wheelchair by 1 year, we could argue that the cost of disability grade III patients would be postponed for 1 year. Given that the trial data for secondary progressive multiple sclerosis suggest that 12 people require treatment for 30 months to save 1 year of wheelchair use, treating 96 people should produce 8 wheelchair-years avoided. From table 7 the cost for a year in grade II is ECU 122 570 for 24 people (therefore ECU 40 917 for eight people), and the cost for a year in grade III is ECU 298 769 for 22.75 people (ECU 105 061 for eight people). The difference (the marginal cost per grade III year avoided) is ECU 64 144 for eight people (ECU 105 061−ECU 40 917). It costs ECU 3.45m (£2.3m) to treat 96 people with interferon β lb for 30 months, assuming ECU 1200 (£800)/month/patient. The net cost of producing 8 wheelchair free years is ECU 3.38m (£2.25m)(ECU 34 500 000−ECU 64 144) . The cost per wheelchair free year is thus ECU 42 2500 (£28 1000).
It is interesting that to offset the costs of disability entirely a drug of similar effect to interferon β lb in secondary progressive multiple sclerosis would need to cost ECU 64 144 for 30 months of treatment for 96 people—that is, ECU 22.27 (£14.83)/ patient/month— assuming that all costs as described are in fact avoided.
The study by Carton et al has limited value as a stand alone exercise. However, further exploration of the data, as above, leads to the conclusion that disability is expensive to treat, although it is clear that if neurologists are going to prevent disability it will have a price, and it would be naive to suggest that a drug with such an effect will pay for itself.