Q: If the correct medication levels for Addison's Disease are established as a result of a day curve test, is it necessary to have further day curves in the future to check the levels, or are they usually constant. I have Addison's Disease and thyroid disease, I have had several day curves and after each one a change of dosage is indicated. Is this in any way caused by my thyroid gland which fluctuates between over and under activity? If this is the case, could you please explain to me why this is so.

A: Regarding consistency of day curve results particularly in patients who also have thyroid disease: It is true that results of day curves of circulating cortisol on hydrocortisone replacement usually remain consistent. This is however not always the case particularly in the early phases of treatment. Certainly fluctuating thyroid function can alter the body's handling of hydrocortisone tablets and if thyroid hormone dosage is changed then it is reasonable to repeat day curve studies. It is my practice to carry out cortisol day curve profiling at the beginning of treatment with hydrocortisone, again at about three months, then at a year and then 2 to 3 yearly thereafter. If I have to change patients' thyroid dosage then I always repeat the hydrocortisone day curve at about 6 weeks. It is unusual for thyroid hormone dosage to have to be changed once full replacement is achieved, although in the early stages of thyroid deficiency disease destruction of the gland is often only partial but progresses with time so the dosage needs to be increased. Another factor to be considered is interaction with other medication which can change the body's handling of hydrocortisone and sometimes thyroid hormone replacement.