Differentiation of patients with primary and thromboembolic pulmonary hypertension.

Twenty-five consecutive patients with obliterative pulmonary hypertension were studied. Primary pulmonary hypertension (17 patients) or chronic thromboembolic pulmonary hypertension (eight patients) was diagnosed by pulmonary angiography or autopsy. Clinical symptoms, physical findings, chest roentgenograms, electrocardiograms, and pulmonary function studies did not differentiate the patients with primary pulmonary hypertension (PPH) from those with chronic thromboembolic pulmonary hypertension (TPH). All eight patients with TPH had a lung scan interpreted as high probability for pulmonary emboli while all 17 patients with PPH had a lung scan interpreted as normal or low probability for emboli. While there was close clinical similarity between patients with PPH and TPH, the presence of a normal or low probability lung scan excluded the diagnosis of TPH.