Can leukemia be misdiagnosed as rheumatoid arthritis?

Can be. . Possibly. Typical symptoms that cause confusion are fever, night sweats. These can be seen in leukemia and many types of lymphomas. It may be worth a visit to the oncologist, if there is any doubt.
Possible! Joint pain can occur in leukemia, and alterations in white cells in number and type can be similar. However, appropriate testing would sort this out!