20 56. The CPT pays particular attention to prisoners held, for whatever reason (for disciplinary purposes; as a result of their "dangerousness" or their "troublesome" behaviour; in the interests of a criminal investigation; at their own request), under conditions akin to solitary confinement. The principle of proportionality requires that a balance be struck between the requirements of the case and the application of a solitary confinement-type regime, which is a step that can have very harmful consequences for the person concerned. Solitary confinement can, in certain circumstances, amount to inhuman and degrading treatment; in any event, all forms of solitary confinement should be as short as possible. In the event of such a regime being imposed or applied on request, an essential safeguard is that whenever the prisoner concerned, or a prison officer on the prisoner's behalf, requests a medical doctor, such a doctor should be called without delay with a view to carrying out a medical examination of the prisoner. The results of this examination, including an account of the prisoner's physical and mental condition as well as, if need be, the foreseeable consequences of continued isolation, should be set out in a written statement to be forwarded to the competent authorities. 57. The transfer of troublesome prisoners is another practice of interest to the CPT. Certain prisoners are extremely difficult to handle, and the transfer of such a prisoner to another establishment can sometimes prove necessary. However, the continuous moving of a prisoner from one establishment to another can have very harmful effects on his psychological and physical well being. Moreover, a prisoner in such a position will have difficulty in maintaining appropriate contacts with his family and lawyer. The overall effect on the prisoner of successive transfers could under certain circumstances amount to inhuman and degrading treatment.