Recognising Susceptible Patients
Identifying patients at risk of NTM
Non-tuberculous mycobacteria pulmonary disease (NTM-PD) has a low prevalence but a big impact. Understanding which patients are most susceptible to developing NTM-PD enables screening to be directed at appropriate patient populations and ensures guideline based therapy can be initiated where needed.
NTM are opportunistic bacteria which rarely cause disease in healthy individuals. However, those with a long-term underlying lung condition or a weakened immune system are susceptible to developing NTM-PD.1 2 For example, chronic respiratory disease has been associated with a 16.5 fold increased risk of NTM-PD.3 Evidence suggests that this predisposition may be due to the chronic epithelial cell inflammation and impaired mucociliary clearance caused by the underlying lung disease.4
Chronic obstructive pulmonary disease (COPD) is characterised by progressive and largely irreversible airflow limitation due to narrowing and fibrosis of the small airways and loss of alveolar attachments as a result of emphysema.5 COPD has been associated with a 15.7 fold increased risk of NTM.3
Bronchiectasis is a long-term condition which causes the airways to become scarred and inflamed. Widening of the airways leads to the build-up of thick mucus which can become infected by bacteria.6 Not only does bronchiectasis increase susceptibility for NTM-PD, but NTM-PD is also likely to exacerbate the underlying bronchiectasis, making both conditions more difficult to treat.7 The overall prevalence of NTM infection in bronchiectasis patients has been shown to be 9.3%.8 However, other studies have shown this figure to be closer to 50%.9 10 A study investigating NTM testing in the UK bronchiectasis population from the EMBARC registry, highlighted that testing rates vary substantially ranging from 8.3% in Northern Ireland to 35.5% in Scotland.11 It is therefore impossible to understand the true extent of NTM prevalence in bronchiectasis patients. Furthermore, a predictive model based on primary care data in the UK indicates that there a substantial number of undiagnosed cases of NTM-PD in the UK.12 Ensuring that testing of at-risk groups becomes more standardised is the only way of fixing this information deficit.
Are there any other characteristics associated with an increased risk of NTM-PD?
Certain physical traits have been closely associated with NTM. For example, NTM shows an increased prevalence amongst people aged 65 or over, more commonly women.7
“Lady Windermere syndrome” is used to describe a specific manifestation of Mycobacterium avium complex (MAC) pulmonary disease which affects elderly women who are immunocompetent and have no significant smoking history or underlying pulmonary disease.13 15 In this instance, disease is limited to the right middle lobe or lingula.14 15 The women affected have been shown to have a distinct body morphotype, characterized by slender habitus, mitral valve prolapse and thoracic abnormalities including scoliosis and pectus excavatum (PEX).15 16
Recognising susceptible patient types.
The following profiles depict patients who may be at risk of developing NTM-PD.