http://www.paed.uscourts.gov/documents/opinions/10D0838P.pdf
SSR 83-20 requires that an ALJ use a medical advisor to determine the onset date of impairments when the onset date must be inferred due to the progressive nature of the impairment.1 See Walton v. Halter, 243 F.3d 703, 710 (3d Cir. 2001) (“[T]his is a situation in which an opinion based on personal, contemporaneous observation was not available. In such a situation, SSR 83-20 calls for an ALJ to have the benefit of expert medical advice based on the best available data without regard to its source.”). The Third Circuit reiterated this requirement in Newell v. Commissioner, 347 F.3d 541 (3d Cir. 2003).
SSR 83-20 states in relevant part:
In some cases, it may be possible, based on the medical evidence to reasonably infer that the onset of a disabling impairment(s) occurred some time prior to the date of the first recorded medical examination, e.g., the date the claimant stopped working. How long the disease may be determined to have existed at a disabling level of severity depends on an informed judgment of the facts in the particular case. This judgment, however, must have a legitimate medical basis. At the hearing, the administrative law judge (ALJ) should call on the services of a medical advisor when onset must be inferred. If there is information in the file indicating that additional medical evidence concerning onset is available, such evidence should be secured before inferences are made. If reasonable inferences about the progression of the impairment cannot be made on the basis of the evidence in file and additional relevant medical evidence is not available, it may be necessary to explore other sources of documentation. Information may be obtained from family members, friends, and former employers to ascertain why medical evidence is not available for the pertinent period and to furnish additional evidence regarding the course of the individual's condition.