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Primary pulmonary hypertension carries a grim prognosis, therefore, it is imperative that prior to reaching this diagnosis, a thorough search be made for all possible causes of pulmonary hypertension. An uncommon cause of pulmonary hypertension amenable to treatment may occasionally be identified. This case report describes a young woman who presented with rapidly progressive right heart failure. Work up for the common secondary causes of pulmonary hypertension was negative, including, congenital intracardiac shunts, left-sided atrial or ventricular heart disease, left-sided valvular heart disease, disorders of the respiratory system including hypoxemia and pulmonary thromboembolic and venoocclusive disease, collagen vascular disease, portal hypertension, HIV infection as well as pulmonary hypertension secondary to drugs and toxins. The only concurrent illness identified was Graves disease. After treatment of hyperthyroidism there was complete resolution of the right heart failure, tricuspid regurgitation, and the pulmonary hypertension. Only a few cases of reversible pulmonary hypertension and right heart failure associated with hyperthyroidism have been reported worldwide. In these patients, the most striking feature has been the normalization of the cardiovascular findings after adequate treatment of hyperthyroidism. The exact reasons for the development of pulmonary hypertension in hyperthyroidism are unclear. Proposed mechanisms include high cardiac output-induced endothelial injury, increased metabolism of intrinsic pulmonary vasodilating substances resulting in elevated pulmonary vascular resistance, and autoimmune phenomenon. Hyperthyroidism should be included in the causes of secondary pulmonary hypertension and/or otherwise unexplained right heart failure. This is especially important because hyperthyroidism is a treatable entity and its cardiac manifestations may be completely reversible.