Pulmonary Tumor Thrombotic Microangiopathy: An Under-Recognized Potentially Fatal Cause of Pulmonary Hypertension

With the increased incidence of cancer, recognizing and managing cancer-related complications have become imperative.Pulmonary tumor thrombotic microangiopathy (PTTM) is a rare, but potentially fatal, complication of cancer that usually presents as rapidly progressing dyspnea and unexplained pulmonary hypertension.1) First described in 1990 by von Herbay et al., it is characterized by intimal hyperplasia of the pulmonary arterioles in response to microscopic tumor emboli attachment to the endothelium.2) The resulting pulmonary hypertension is primarily due to histopathologic changes in the vasculature and secondary thrombosis, rather than direct vascular obstruction by the large tumor emboli.3) Given its pathology, PTTM should be considered in patients with cancer in the following scenarios: 1) unexplained, rapidly progressive dyspnea, 2) presence of pulmonary hypertension on echocardiography without any apparent cause, and 3) absence of pulmonary arterial thrombus on chest computed tomography (CT).Further studies, such as perfusion scans, right heart catheterization, or lung biopsy, should be performed in these patients.However, these additional studies often cannot be performed because of the unstable clinical conditions.Moreover, unfamiliarity with the disease entity (e.g., when to suspect and how to evaluate suspected PTTM) hinders early diagnosis and timely management.From this perspective, the study by Bak et al. 4) in the current issue of the Korean Circulation Journal is noteworthy.The authors elegantly described the clinical features and progression of suspected cases of PTTM.A total of 28 cases were collected over 10 years at a tertiary center.Among the 28 cases, PTTM was histologically confirmed in only one, which shows the difficulty in obtaining a confirmatory diagnosis by biopsy.In clinical practice, PTTM is primarily a tentative diagnosis made through a combination of clinical history, physical examination, echocardiographic and CT imaging, and laboratory examination in patients with cancer.In addition to PTTM being a diagnostic conundrum, this study showed that the clinical course of suspected PTTM is rapid and fatal.Most patients with New York Heart Association class 4 dyspnea or desaturation died within 1 week.The median time to death from right ventricular (RV) failure onset was only 3.8 days.All the patients with suspected PTTM died.Although chemotherapy delayed death, its effect was minimal.