U.S. Senator Dianne Feinstein, who returned to Washington in May after a months-long absence due to shingles, suffered more complications from the illness than were publicly disclosed, the New York Times reported on Thursday.

The shingles caused a rare complication known as encephalitis, inflammation of the brain, the New York Times said, citing two people familiar with the senator's diagnosis.

The 89-year-old Democrat had been sidelined since February as she recovered from shingles, which had led to calls from some fellow Democrats that she step aside and allow someone else to take her place.

Feinstein's absence had deadlocked the Senate Judiciary Committee she sits on, slowing Democrats' drive to approve some of President Joe Biden's most controversial nominees to vacant federal court positions, leading to a partial Republican blockade.

Feinstein, who will not seek re-election in 2024, said on May 10 that said she would work a lighter schedule as she returned and that she was experiencing some side effects, which included vision and balance impairments.

Asked for a response, Feinstein’s office pointed to her comment in the New York Times article where she said: "I’m back in Washington, voting and attending committee meetings while I recover from complications related to a shingles diagnosis. I continue to work and get results for California."

(Reporting by Costas Pitas in Los Angeles; Editing by Caitlin Webber and Alistair Bell)