What consistutes the proper domain of psychiatric treatment ?
One reason that neurologists do not treat psychiatric illness is that they have, by preference, chosen to treat a more narrow range of illnesses.
The propoer domain of psychiatric illness is any illness for which either the origin of the illness is in the central nervous system (such as dementias), or produces features that disturb the central nervous system (such as delirium).
Neurologists have taken, from this set, their own chosen domain -- epilepsies, motor illnesses (suchs as ALS and Parkinson disease), and even myophathies (muscular dystrophy is an example.) So, neurologists treat only illnesses of the central nervous system for whci hthe patient's express concern is focused on motor dysfunction.
To make the picture even more casual, neurologists do not treat fibromyalgia, and leave this for rheumatic disease specialists, presumably because of the pain being present.
A broad generalization would then be that, in addition, because of the myesthemic features of the illness, neurologists should be managing chronic fatigue syndrome.
In addition, because of the peculiarities of the legal system in the U.S. (DHHS regulation and Federal statutes), pulmonoloists manage primary sleep disturbance illnesses. Per statutory and regulatory provisions, then, sleep disturbances (circadian rhythm disorders, apneas, inclding central apneas, REM disturbances, RLS, and PLMD) fall within the scope of pulmonary practice. This is a real disadvantage to patients who are relying on pumonologists to provide care for this set of CNS orginating illness, but this can be referred to an understanding that medical practice is determined in many cases by existing Federal and state statutes, and related regulatory extensions.
Perhaps, then, another way of putting it is that psychiatrists treat those illnesses of the central nervious system that have not been determined by Federal of state law to be treated by other medical specialities. This provides a legal definition of psychiatric illness, which is entirely in keeping with the role of politics and society in attempting to govern the care of psychiatric patients.
The reason that this is such a dominant feature of our legal system will be left to another article.