Traditionally, the taxonomy of ilklness has been pursued in this fashion. Ilnesses are classified by organ, then by tissue, and the by temporal behavior of those tissues.
One example of this is the system of classification of cardiac rhythm diseases.
However, in the domain of psychiatric illness such an approach has not been pursued, at least in the past.
We can ask why this is, The reason becomes apparent if we look at the structure of the central nervious system. Distinct portions of the brain, participate in the same tasks, and one anatomical structure can have many diffierent tasks.
If we examine cardiac nerve controls, each pathway has a distnct, and relatively unique task. The same can be said for peripheral motor nerves.
In some cases, illnesses in these structures are defined by the microscopic pathology found on examination following biopsy or autopsy.
To a certain extent, psychiatric taxonomy has implicitly utilizated such an approach, but only implicitly. For example, diseases leading to disturbance of sensorium are not localized to the extended nerve network that maintains intact sensorium. And yet, the entire group of illnesses are assembled under the topic of delirium.
Thus, it is necessary to recognize that we have a choice. We can divide illnesses based by task (by biological task) or by source of illness.
In some cases, these two methods of classification will obtain the same result.
One example of this is the occurence of substance dependence and abuse, in populations in which the bioological function of maintaining sobriety is overwhelmed, and at the same time, is usually linked to a unique causation (a specific recurrent substance exposure). The concurrence of these two classification methods, in this case, leaves us still with a difficult choice.
IN the attached article on etiology of psychiatric illness, we can see that, for any given functional group within the central nervious system, sources of illness, although often narrow, can be quite wide, returning use to the former classification method.
Let use take another example. Many refractory psychologic illnesses are characterized by both environmental and genetic causation. For some patients, one source is much more important.
This is, appraently, true also for substance dependences.
And, for pataients with sociopathies, we also find this to be the case.
In order, therefore, to truly refine how we go about creating taxonomies of illness, we should be able to describe the course of the illness, and then begin with a description not based on the eitology or all the fucntional netwroks, but rather the initial functional network that becomes ill.