Is it true that thyroid problems could be misdiagnosed as bipolar or visa versa?

Thyroid: Possible due to mood cycling especially in early stages.

Only at 1st glance.: While it's unlikely that symptoms of anxiety or depression would be the only evidence of thyroid disease, they can be in the mix. Thyroid disease most often has lab results and symptoms like weight gain/loss, fatigue/restlessness, sensitivity to hot/cold, bowel movement changes, and menstrual irregularities. Good professionals will know the difference. But, you can suffer both, so have it checked.

Not quite: Hypothyroidism can be misdiagnosed as major depression.