Schumacher has been in a medically induced coma in Grenoble, France, since being badly injured in a ski accident on December 29 in the French resort of Meribel with his son and friends.
Kehm said Schumacher's family have been touched by a deluge of tributes and support from fans of the racing driver, but constant media speculation, particularly in German newspapers, have caused the family some anguish.
"What upsets the family most is media quoting doctors who are not treating Michael and untruths are constructed from these," said Kehm, who has been in Grenoble nearly every day since the accident.
"It has been a problem when outsiders comment and it means we have to set the record straight, even when we don't want to."
The 45-year-old Schumacher underwent two operations in the days after the accident to remove life-threatening blood clots before being placed into a coma.
The family announced at the end of January that drugs used to keep him in his deep sleep were being reduced with a view to bringing him back to consciousness.
-AAP