When reviewing an ERISA claim by a fiduciary under a long term disability benefit, can the court admit more evidence that was before the decision was made?

When reviewing an ERISA claim, the court is ordinarily limited to the administrative record the plan administrator had at the time of the benefit denial. See Abatie, 458 F.3d at 970. This restriction is based on the principle that federal district courts should not function "as substitute plan administrators," and that expanding the record on appeal "would frustrate the goal of prompt resolution of claims by the fiduciary under the ERISA scheme." Taft v. Equitable Life Assurance Soc'y, 9 F.3d 1469, 1472 (9th Cir. 1993) (citation omitted). Where, as here, the court reviews an ERISA claim de novo, it can admit outside evidence "only when circumstances clearly establish that additional evidence is necessary to conduct an adequate de novo review of the benefit decision." Mongeluzo v. Baxter Travenol Long Term Disability Benefit Plan, 46 F.3d 938, 944 (9th Cir. 1995) (citation omitted). In most cases where review is de novo, "additional evidence is not necessary for adequate review of the benefits decision, [and] the district court should only look at the evidence that was before the plan administrator . . . at the time of the determination." Id.