Actually, intermittant leave is not a reasonable accommodation which the employer must grant under the ADA in any event. A reasonable accommodation is some change in rules/procedures, or some provision of assistance technology/devices, which is not too expensive or disruptive and which lets you be at work and do your job. Not being at work--taking leave--is not a "reasonable accommodation" under the law. Rather, the FMLA was passed to allow employees (unpaid) leave time when necessary for medical reasons. Therefore, they do not have to grant your ADA request and can insist you use FMLA.