Thyrotoxicosis is listed as a cause of pulmonary arterial hypertension (PAH). The aetiopathogenesis remains largely uncertain, but an autoimmune mechanism has been postulated, among others. In this setting, other causes of PAH need to be actively sought and excluded prior to attributing it to the thyrotoxicosis. The importance of recognising this condition is that it is usually reversible with restoration of a euthyroid state. We describe three patients who presented with thyrotoxicosis and features of PAH in whom other causes were excluded with various investigations. We also demonstrated reversibility of the pulmonary hypertension upon restoration of a normal thyroid state
