The diagnosis 242.9 requires a 5th digit. Either 0 (without mention of thyrotoxic crisis) or 1 (with mention of thyrotoxic crisis) the doctor needs to tell you which one it is. Just correcting the diagnosis may be enough.
This diagnosis alone may not be enough to warrant a 99204. The guidelines for what constitutes a 99204 are that it must be a comprehensive history, a comprehensive examination, and decision making of moderate complexity.
You may also want to check the LCD's for your area. Medicare has some pretty specific guidelines for diagnosis.