Lamar has been hospitalized at Cedars-Sinai Medical Center in L.A. for a month, and Khloe has been a frequent visitor.
We're told Khloe has a lesion on her leg which became incredibly painful. She developed a high fever, swollen glands. She's also sweating profusely with intermittent chills.
One very connected source tells TMZ, "It's so scary. She's so sick."
Khloe cancelled several appearances for her book promotion, tweeting, "I'm sick & dr's orders are that I need to lay low until we narrow down what's wrong."