Inhaled corticosteroid use is associated with an increased risk of non-tuberculous mycobacterial pulmonary disease in older patients with obstructive lung disease.

The Canadian study of more than 417,000 patients aged ≥66 years with asthma, COPD or asthma-COPD overlap syndrome (ACOS) found the association was significant for COPD and ACOS patients but not for those with asthma alone.

It found a strong dose-response relationship between incident non-tuberculous mycobacterial pulmonary disease (NTM-PD) and inhaled corticosteroid (ICS) exposure over 12 months. The association was significant for fluticasone but not budesonide or other steroids.

The species causing NTM-PD were primarily Mycobacterium avium complex (MAC) and M. xenopi.

The researchers said their findings suggested a casual relationship between ICS use and NTM-PD although it was likely only one factor in a multifactorial pathway.

Patients with NTM-PD were more likely to also have bronchiectasis, interstitial lung disease or prior TB than control patients.

They concluded that while NTM-PD was still relatively rare it was clinically important due to its chronicity and the fact it was difficult to treat.

The researchers estimated 1,775 COPD patients would need to be treated with ICS for one patient to be harmed by NTM-PD compared to just 20-33 treated patients for one to develop pneumonia.

Associate Professor Grant Waterer, from the Royal Perth Hospital and University of Western Australia, said the findings were consistent with two other studies.

“The problem is that COPD itself is a risk factor for NTM, as may be oral corticosteroids. With the retrospective database design it is impossible to tease out the various confounders,” he said.

“The only real conclusion is that clinicians should be aware of NTM disease in patients with COPD who develop bronchiectasis, nodules or cavities.”

Associate Professor Waterer said the data was insufficient for clinicians not to use ICS.

However he said caveats such as using the lowest effective dose – probably 100mcg fluticasone furoate or 250mcg twice daily fluticasone proprionate – and possibly only in those with peripheral eosinophil counts >2% would be cautionary.

“Although we await the eosinophil breakdown of the recently announced GSK triple therapy study that showed ICS/LABA/LAMA superior to LABA/LAMA for exacerbations,” he added.