Study: TB may be ‘one of the most important’ causes of group 3 PH
Further, individuals who were treated for TB more than once had a higher risk of developing PH compared with those who only had one episode of tuberculosis.
“This report provides further impetus for research into PH-post-TB which may be one of the most important and underappreciated causes of group 3 PH worldwide,” the researchers wrote.
The team noted that the newest guidelines on group 3 PH, which is linked to lung diseases, do not list TB or a history of tuberculosis treatment as a risk factor.
The study, “The prevalence of pulmonary hypertension after successful tuberculosis treatment in a community sample of adult patients,” was published in the journal Pulmonary Circulation.
PH is a progressive disease associated with high blood pressure in pulmonary arteries, the blood vessels that supply the lungs. The chronic disease causes overexertion of the heart and can lead to heart failure.
The World Health Organization (WHO) classifies PH into five groups, based on the cause of the disease. Group 3 PH includes disease caused by oxygen deficiency, known as chronic hypoxia, and lung disorders, such as chronic obstructive pulmonary disease and obstructive sleep apnea.
Some experts have noted that pulmonary hypertension developing after TB is associated with a worse prognosis than PH derived from other group 3 causes. However, knowledge is lacking on PH prevalence after TB treatment.
To provide more data and clarity on this subject, an international group of researchers collaborated on a study, in South Africa, to assess the prevalence of PH in patients who had completed TB treatment.
The team enrolled a random selection of individuals from a low-to-middle-income suburb in Cape Town, who had completed TB treatment at least one year prior to the study.
The analyses included 100 adults with no active TB, 71 of whom were male, with a mean age of 42. Most participants were smokers (72) or ex-smokers (12), and 24 had no lingering symptoms after TB treatment.
To assess PH prevalence, participants underwent transthoracic echocardiography (TTE). Specifically, TTE was used to estimate pulmonary artery systolic pressure (PASP) — the pressure in the pulmonary artery during a heartbeat — as the main measure to screen for PH.
Participants were classified as having probable PH if PASP was 40 mmHg or higher, and possible PH if PASP was 35–39 mmHg and they had other TTE features of PH. A finding of no PH was made if PASP was lower than 35 mmHg.
Although right heart catheterization, an invasive approach, is the gold standard to diagnose PH, TTE is more available in low-to-middle income countries, the team noted. Thus, it represents an important noninvasive tool in these nations.
Participants also reported any symptoms, did a six-minute walk distance (6MWD) test to assess their exercise capacity, and underwent a spirometry analysis, which is a standard test of lung function. This test included parameters such as forced vital capacity, or how much air can be exhaled after a deep breath, and forced expiratory volume in one second (FEV1), or how much air can be forcefully exhaled in one second.
Of the 100 participants analyzed, nine (9%) had probable PH and a further seven (7%) had possible PH. The number of times a participant was treated for TB (or TB episodes) was significantly associated with having probable PH, with the odds of having probable PH after TB treatment increasing 2.13 times with each additional TB episode.
“The unexpectedly high prevalence of probable PH in this non-healthcare seeking population has important implications for the epidemiology of PH secondary to [chronic lung disease],” the research team wrote.
Smoking also led to higher odds of probable PH, but this finding was not statistically significant. The high proportion of smokers in the group — all participants with probable PH were smokers or ex-smokers — “makes isolation of the contributing role for smoking difficult, both in the development of PH and the high proportion of lung function abnormalities,” the researchers wrote.
Most participants (78%) had abnormal lung function, but no associations were found between these measures and probable PH. Likewise, age, HIV status, 6MWD values, and participant-reported symptoms (including cough, sputum, wheeze, and shortness of breath) were not associated with probable PH.
“This lack of correlation between PH, symptoms, lung function and 6MWD is important in that they do not appear to be useful in identifying patients at risk of PH [after TB treatment] during screening,” the researchers wrote. Yet, they noted that studies with larger groups of participants are needed to better understand the relationship between PH and post-TB symptoms and lung function.
In conclusion, the high prevalence of probable and possible PH in this group of TB survivors provides much needed evidence on the importance of screening for PH in this population, according to researchers.
“TB and PH-post-TB has been omitted from guidelines as a potential cause for group 3 PH, compounding neglect for this condition,” the team noted.
One study limitation, the team also noted, was that their research involved only one community.
More studies in larger and more diverse populations are needed, using both TTE and right heart catheterization, to clarify the link between PH and TB survivors, the researchers said. This will allow for a better determination of the merits of screening patients with a history of tuberculosis with successful treatment for pulmonary hypertension.
By Joana Vindeirinho, PhD
Source : Pulmonary Hypertension News
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