Heather Walker said the overnight respite provision for 14-year-old Peter, who has cerebral palsy, epilepsy, is paralysed on one side and cannot speak, has recently been cut.
She is now only able to leave him at a Priors Hill Children's Centre in Macclesfield on Saturdays and for five hours every other Wednesday.
Mrs Walker, 54, said the strain of looking after Peter – whom she adopted 10 years ago - was proving too much and she felt she had no option but to return him to care.
Her plight was highlighted a week after Riven Vincent accused Mr Cameron of reneging on an election promise to continue providing support for her daughter Celyn.
The prime minister, whose disabled son Ivan died in 2009, met Miss Vincent on the campaign trail and assured her the NHS would be safe.