Maine Senator Susan Collins is disclosing that she has had a condition known as an essential tremor during her career in the Senate.

The Press Herald reports Collins says the condition is benign and does not interfere with her work.

She says the tremor has been the subject of “cruel comments online,” but does not effect her work.

The Mayo Clinic defines an essential tremor as a common, often inherited, neurological disorder causing involuntary, rhythmic shaking, usually in the hands and arms, but also affecting the voice.

Collins has served in the Senate since 1996, and is seeking her sixth term in this year’s election.

She’s a Republican who is facing presumptive Democratic nominee Graham Platner.