Hyperthyroidism
Hyperthyroidism as a causative agent of gynecomastia is reported in about 10-40% of cases. Hyperthyroidism itself involves metabolic derangement and hormonal imbalance of the thyroid gland. This disruption can also overlap with the metabolism of testosterone, causing a dip in its circulating concentration. Estrogen increase is also seen in hyperthyroidism. Gynecomastia secondary to this cause is, however, reversible with the treatment of thyrotoxicosis.