Wiki Sleep study- does Medicare allow more than 1 a year

[Susan22]

Checking to see if anyone knows of a MEdicare policy or bulletin that specifies if Medicare will pay for a sleep study more than 1 time a year or how often will they pay? Is it a yearly allowance? or diagnosis driven? Example: Patient had sleep study in 9-2010, however due to the diet the patient has been on the Dr. would like to do another sleep study.
Thanks