Aetiology of intellectual disability - the Finnish classification: development of a method to incorporate WHOICD-10 coding

The present authors made an attempt to ease the diagnostic work of physicia ns who have patients with intellectual disability by creating an aetiologic al classification system based on the time and mechanism of injury to the c entral nervous system (CNS). The current paper presents the work-up needed for understanding at least the timing of the causative factor/factors. The timing principle opens a direct course to family counselling. This method h as been very well accepted during its 18 years of use in Finland, and there fore, it was felt that It would be helpful to organize the relevant ICD-10 diagnoses according to the timing principle. This method has been published as a manual. An image of a tree became the obvious metaphor for this syste m. The genetic category forms the main root and stem, from which multiple b ranched roots and limbs emerge. The individual diagnoses appear as root nod ules and leaves. The system is flexible making it possible to add new branc hes for groups of diagnoses when improved diagnostic methods create these o ptions (e.g. microdeletions). The aetiological diagnoses change accordingly . Over the course of further development, new incidents damaging the CNS ma y affect the functional level of an individual and require additional diagn oses. It is a constant challenge for physicians to keep the diagnoses of th eir patients up to dare. The image of the tree helps professionals to think in terms of timing, and thus, makes family counselling easier. It is also helpful in the education of medical professionals.