Approximately half of adults with idiopathic pulmonary arterial hypertension (IPAH) had nonplexiform vasculopathy characterized in part by severe pulmonary microvascular remodeling, based on data from 50 individuals.
The clinical phenotype of IPAH was historically described as a rapidly progressive rare disease in young women and characterized by plexiform lesions, wrote Esther J. Nossent, MD, of Amsterdam University Medical Centers, Amsterdam, the Netherlands, and colleagues. However, the patient population with IPAH has become older and predominantly men, and the nature of vascular phenotypes and histologic patterns in patients with contemporary IPAH has not been well studied, the researchers said.
In a cross-sectional study published in CHEST, the researchers reviewed lung histology data from 50 adults with IPAH that had been assessed by two experienced pathologists. The mean age of the patients was 52 years and 58% were women. Based on a histopathologic evaluation, 24 patients had nonplexiform vasculopathy (48%) and 26 had plexiform vasculopathy (52%). Notably, microvascular remodeling involving arterioles and venules was substantial in patients with nonplexiform vasculopathy but mild or absent in those with plexiform vasculopathy, the researchers wrote.
The researchers also compared the clinical characteristics of patients with plexiform vs nonplexiform vasculopathy. Hemodynamic parameters were similar in both patient groups. However, those with nonplexiform vasculopathy were significantly older than those with plexiform vasculopathy (60 years vs 44 years), more likely to be men (67% vs 20%), and had a lower diffusing capacity of the lungs for carbon monoxide (DLCO) at diagnosis (all P < .001). Patients with nonplexiform vasculopathy also were significantly more likely than those with plexiform vasculopathy to have a history of smoking (P = .03). Genetic testing revealed no mutations in established PAH genes in the nonplexiform group.
Low DLCO has been associated with worse outcomes regardless of hemodynamic response, the researchers noted. In the current study, "a DLCO of < 45% almost perfectly identified patients with nonplexiform vasculopathy with prominent pulmonary microvascular disease," they said.
The findings were limited by several factors, including the small study population and the higher frequency of surgical lung biopsies in the nonplexiform group vs the plexiform group, which is not part of the general workup of patients with IPAH, the researchers noted.
More research is needed to better define the subgroup of patients with IPAH with nonplexiform vasculopathy and to identify the causes, biological features, and treatment approaches for these patients, they said. However, the results suggest that differences between patients with IPAH with plexiform vasculopathy and those with nonplexiform vasculopathy could ultimately inform targeted treatment strategies.
"Recognizing these clinical phenotypes allows revisiting current datasets to understand better the potential future clinical consequences of the vascular phenotypes for treatment response and clinical outcome," the researchers concluded.
Findings May Inform More Targeted Therapy
"Any investigation that adds substantive insight into a complex disease that can translate into a better understanding of clinical patient phenotypes and eventually into improved treatments and patient outcomes has relevance at any time," said Paul Forfia, MD, professor of medicine at the Lewis Katz School of Medicine at Temple University, Philadelphia, in an interview.
"There is focus on the antiproliferative forms of pulmonary arterial hypertension–specific therapy, and the results of the current study may have implications to these therapies," said Forfia, who was not involved in the current study.
"In the current study, the investigators show that 48% of patients that were traditionally categorized as IPAH had a vascular phenotype that is not considered 'typical' or classic for IPAH," Forfia told Medscape Medical News. "These findings highlight a significant heterogeneity of the pulmonary vascular phenotype within IPAH, which raises the question of whether the nonplexiform patient would be less responsive to the novel, antiproliferative forms of therapy," he said.
The new findings are quite interesting but not surprising, Forfia said. "The World Symposia diagnostic groupings for pulmonary hypertension are a very important and necessary form of categorization and differentiation amongst forms of PH [pulmonary hypertension], and these groupings make a best attempt based on available evidence to separate patients of varying PH pathophysiology, both in terms of diagnosis and in how PH patients are treated," he explained.
"However, clinical experts in PH have known that subphenotypes of PH pathophysiology exist within group I PAH, as well as in PH related to left heart disease (group 2), chronic respiratory disease (group 3), and chronic thromboembolic disease (group 4)," he said.
Findings from the current study reinforce the importance of clinical and physiological phenotyping of each patient, which can help in terms of therapy selection and in managing expectations in response to therapy, Forfia added.
"Perhaps the most evident and important clinical implication from the current study is to remind clinicians treating patients with PH that heterogeneity exists within the vascular phenotype and clinical makeup of patients even within the same type of PAH," Forfia told Medscape Medical News. "With this insight, clinicians are more informed and thus more apt to consider nuances in the diagnosis, treatment, and expectations for treatment response within PAH," he said.
Forfia also highlighted the potential implications of the association between cigarette smoking and the nonplexiform vascular phenotype. "This association was present in the absence of radiographic evidence of emphysema and raises the provocative notion that cigarette smoking may lead to pulmonary vascular abnormalities, perhaps even PAH, in patients without a diagnosis of emphysema," he said.
"An important limitation from the current study is that the vascular phenotypes observed within their cohort of IPAH patients were obtained from histopathology specimens at the time of autopsy, explant at the time of lung transplantation, and surgical lung biopsy spanning over a 22-year period," Forfia noted. Additional research is needed to explore how vascular phenotypic differences can be appreciated in the absence of histopathology and how these differences could impact therapy selection and patient outcomes, he said.
The study received no outside funding. Nossent disclosed receiving speaker fees from Janssen, MSD, and United Therapeutics/Ferrer and consulting fees from Janssen and United Therapeutics/Ferrer. Forfia had no financial conflicts to disclose.