While brain disorders pose a significant economic burden to the State, figures outlining their cost are at best "a rough estimate," experts have said.
Data for the Republic from the Cost of Disorders of the Brain in Europe (CDBE) study suggest that the direct and indirect cost of neurological and psychiatric disorders was €3 billion in 2004.
This represents 3 per cent of our gross national product and costs each Irish citizen €775 per year.
The research found that 1.1 million people here were affected by a brain disorder.
However, none of the costs could be calculated from Irish data, and the prevalence figures for individual diseases were estimated from known European rates.
Writing in the Irish Medical Journal, Dr John McHugh and Dr Ray Murphy of the Adelaide, Meath and National Children's Hospital (AMNCH), Tallaght and Dr P Sobocki of the Karolinska Institute in Stockholm say: "The results can serve at best as a rough index rather than an accurate reflection as practically all of the information is extrapolated and adjusted from other European data."
The brain disorders included in the CDBE study were addiction, affective disorders such as depression, anxiety, brain tumours, dementia, epilepsy and migraine.
Also included in this study were multiple sclerosis (MS), Parkinson's disease, psychotic disorders such as schizophrenia, stroke and trauma to the brain.
The most prevalent neurological disorder was migraine, estimated to affect 335,000 people. Anxiety disorders were the most common psychiatric problem, with a prevalence of 370,000 cases.
An analysis found that brain tumours and multiple sclerosis were the most costly brain disorder per individual affected. Anxiety disorders and migraine had a relatively low cost per case but were more prevalent.
Overall, the direct health costs of brain disorders amounted to €891 million, representing 29 per cent of total costs.
Indirect costs of €1.7 billion were mainly due to loss of production associated with sick leave.
The authors say that the CDBE costs for multiple sclerosis underestimate the true cost to the Republic by 60 per cent.
"The total cost of MS in the CDBE is estimated at €65 million per annum.
"The true figure is closer to €150 million, which is in line with the annual cost estimates for stroke and epilepsy."
Drug treatment costs for brain disorders are also underestimated, they say.
While the CDBE estimate for drug costs is €61 million, the authors calculate that the combined cost of drugs for medical card patients, those availing of the drugs payment scheme and the long-term illness scheme comes to a total of €216 million, over three times the CDBE estimate.
"The publication [ of European data] argues the need for properly resourced epidemiological research in relation to disorders of the brain in Ireland to further refine the extrapolated estimates," the authors note.
"The direct medical costs for brain disorders is relatively small when compared to the overall expense and indirect costs, indicating that resources might best be targeted at prevention," they add.
Asked to comment on the research, Dr Orla Hardiman, consultant neurologist at Beaumont hospital, in Dublin, said: "It does underline the need for better data collection."
Dr Hardiman also pointed out that the national needs assessment in neurology that is being undertaken by the Health Service Executive (HSE) at present, could be hampered by a lack of exact data.