The overlap syndrome

There is more than one 'overlap syndrome' in medicine.  For respiratory and sleep physicians, however, the term generally refers to patients with the combination of chronic obstructive pulmonary disease (COPD) and obstructive sleep apnoea (OSA).

Such patients will often have profound oxygen desaturation associated with their OSA.  They are also more likely than patients with either syndrome alone to develop pulmonary hypertension.

A joint Spanish-American study in the blue journal this month has looked at this condition in quite a helpful way.  They wanted to find out if patients with the two of these conditions together did worse than patients with just COPD.  And if they did worse, did treatment with CPAP seem to make any difference?  They took three groups of around 200 patients each.  One group had patients with the 'overlap syndrome' on no treatment.  Another group had patients with the 'overlap syndrome' on CPAP.  The third group was patients with COPD alone.

They recruited patients for 5 years from 1996 to 2001 and then followed them. The patients were selected from patients referred to a sleep clinic - so the patients with COPD alone were chosen from amongst a population of snorers who had no OSA.

Amongst those patients with OSA (defined as an apnoea-hypopnoea index over 5) and COPD, CPAP was recommended to all.  So the 'not treated' group were those who ended up being non-compliant with CPAP therapy.  As always, this raises the question of whether they make other good health-related choices (ie is non-compliance with CPAP a marker of bad health behaviours rather than in itself an unhealthy choice?).  

The bottom line was that 213 patients died.  Death from any cause, and particularly death from cardiovascular causes, were more frequent in untreated overlap patients (RR 2.23, C=95%CI 1.59-3.14)than in the overlap/CPAP treated group.  There was no significant difference between the overlap/CPAP group and the COPD -alone group.

Likewise, untreated overlap patients were more likely to have a first admission to hospital with an exacerbation (OR 2.13, 95% CI 1.61-2.80) than COPD only patients.

So, what have we learned?  In patients with COPD, the coexistence of OSA is a poor prognostic marker, indicating higher risk of hospitalisation with exacerbation and higher risk of death.  That increased risk is not evident in patients with COPD and OSA who use CPAP. 

This means that prescription of CPAP for COPD patients who have OSA is one of the very few interventions which may make a difference to mortality outcomes and is, therefore, VERY IMPORTANT.