"Primary" pulmonary hypertension, eosinophilia, and filariasis in Ceylon.

;Primary' pulmonary hypertension, which is rare in western countries, was found to be relatively common in Ceylon. The clinical and haemodynamic features were studied. There were two distinct types of the disease, malignant and benign. Patients with the malignant form of the disease had a rapidly progressive illness of short duration and an invariably fatal outcome. Those with the benign form gave a long history and, in spite of severe pulmonary hypertension, were only slightly disabled. They seemed to tolerate the disease better. An important factor which determined the clinical course of the disease was the patency of the foramen ovale. This appeared to act as a safety valve permitting a right-to-left shunt in times of stress. The foramen ovale was closed in all patients with the malignant type. The therapeutic implications of this need further study. Many patients with ;primary' pulmonary hypertension had an unusually high eosinophil count (normal range for Ceylon, 0-500 per cu.mm.). Patients in hospitals often have higher counts ranging from 0-1000 per cu.mm. due to intestinal parasitic infestation. Patients with ;primary' pulmonary hypertension were found to have a significantly higher mean eosinophil count than age-matched, sex-matched controls admitted to the Cardiology Unit with chronic rheumatic heart disease and congenital heart disease. The higher count was not due to intestinal parasitic infestation, and none of the other known causes of a raised eosinophil count were present. Four patients had eosinophil counts over 3,000 per cu.mm., the range commonly associated with tropical pulmonary eosinophilia, a disease caused by filariasis. These patients did not manifest any of the symptoms of tropical pulmonary eosinophilia. Patients with ;primary' pulmonary hypertension were examined for evidence of filariasis (clinical, haematological, and serological). Volunteers from among patients with tropical pulmonary eosinophilia and symptom-free patients positive for Wuchereria bancrofti microfilaria were similarly tested and also catheterized for evidence of pulmonary hypertension. The results of these investigations and their significance are discussed. The geographical incidence of ;primary' pulmonary hypertension and filariasis was similar. Filarial worms are known to cause pulmonary hypertension in animals. There is sufficient evidence to suspect that the same may be true in humans. This may explain the high incidence of the disease in Ceylon and its unusually high prevalence among men.