TPO and hyperthyroidism: One possible mechanism that may be involved in the association between TPO-abs and RCBD is the episodic alternating of hyperthyroidism (due to leakage of thyroid hormone from autoimmune-destructed thyrocytes) and hypothyroidism (due to a transient loss of functional thyrocyte mass) [22], since a neuromodulatory link has been found between the hypothalamic-pituitary-thyroid axis (HPT-axis) and serotonin [51–53] or β-adrenergic receptors [54] in the limbic region, a major part in charge of mood regulation.