Medical reports containing descriptions of examinations or treatment of the individual
are basic to the determination of the onset of disability. The medical evidence serves
as the primary element in the onset determination. Reports from all medical sources
and entities that maintain medical sources’ evidence (e.g., physicians, hospitals,
and government agencies) which bear upon the onset date should be obtained to assist
in determining when the impairment(s) became disabling.
With slowly progressive impairments, it is sometimes impossible to obtain medical
evidence establishing the precise date an impairment became disabling. Determining
the proper onset date is particularly difficult, when, for example, the alleged onset
and the date last worked are far in the past and adequate medical records are not
available. In such cases, it will be necessary to infer the onset date from the medical
and other evidence that describe the history and symptomatology of the disease process.
Particularly in the case of slowly progressive impairments, it is not necessary for
an impairment to have reached listing severity (i.e., be decided on medical grounds
alone) before onset can be established. In such cases, consideration of vocational
factors can contribute to the determination of when the disability began. (See DI 25501.200 - DI 25501.470 for information about determining the established onset date.)