What major concern arises when using PTU as a treatment for Graves' disease?

The major concern when using Propylthiouracil (PTU) as a treatment for Graves' disease lies in its potential to cause immunosuppression. PTU is an antithyroid medication that helps to lower thyroid hormone production. However, one of its serious side effects is agranulocytosis, a condition where the white blood cell count drops significantly, leading to increased susceptibility to infections. This immunosuppressive effect can be particularly concerning, as it can make patients more vulnerable to various infections and complicate the management of the disease.

In the context of treating hyperthyroidism, especially in the case of Graves' disease, careful monitoring of the patient's white blood cell counts and general health status is crucial to mitigate the risks associated with immunosuppression while on PTU. Other options presented do not explicitly relate to the primary concerns regarding PTU use in this context. For instance, concerns like hypocalcemia, thyroid storm, and hyperlipidemia are not directly related to the use of PTU and its primary side effects in the treatment of Graves' disease.