Pulmonary hypertension secondary to thrombocytosis in a patient with myeloid metaplasia.

A 72-year-old physician with myeloid metaplasia developed marked thrombocytosis, pulmonary hypertension, and right heart failure following splenectomy. No cause for the pulmonary hypertension could be found. The pulmonary hypertension and right heart failure returned to normal when hydroxyurea therapy corrected the thrombocythemia. It is concluded that thrombocytosis may cause pulmonary hypertension, mediated by pulmonary capillary obstruction from cellular components, involving platelet aggregation, microthrombosis, and stasis, and possible vasoconstrictor effects.