Endocrine Abstracts

We have previously described a series of patients who presented with clinical and biochemical features diagnostic of phaeochromocytoma but in whom catecholamine excess proved to be secondary to undiagnosed obstructive sleep apnoea (OSA). We describe here a prospective study of 30 patients presenting to the sleep clinic with OSA from whom 24 hour urine collections were analysed for catecholamines before and after treatment with continuous positive airways pressure (CPAP).

21 patients had excretion of noradrenaline (NA) <560 nmol/24h (95th centile) and 9 patients were found to have excess excretion >560 (p<0.0001: chi-square test). A phaeochromocytoma or paraganglioma was excluded by CT and MIBG uptake scanning in 'NA excess' patients.

CPAP treatment normalised NA excretion in NA excess patients: mean excretion fell from 684.1 nmol/24h +/- 114.8 to 395.2 +/- 158.9 (p=0.0208). No significant effect on NA excretion in NA normal patients was seen.

Systolic and diastolic BP were not found to be significantly different between the two groups. CPAP treatment was found to significantly reduce the diastolic BP in all patients from a mean of 88.5 mmHg +/- 14.52 to 80.31 mmHg +/- 11.78 (p<0.001). This was true for both NA excess and NA normal patients. The systolic BP of all patients was not found to change significantly post CPAP (p=0.0587).

There was no significant difference in apnoea/hypopnoea index between NA excess and normal groups, but the NA excess group was found to have a significantly higher desaturation index (p=0.0122).

We conclude that a significant proportion of patients with OSA have excess catecholamine secretion, due to sympathetic activation during periods of desaturation. OSA is an important cause of pseudophaeochromocytoma. Treatment with CPAP is effective in reducing catecholamine secretion in patients with excessive secretion and this effect may in part underlie the reduction in BP seen with CPAP.