Does ambulatory blood pressure monitoring improve the diagnosis of secondary hypertension?

Ambulatory blood pressure monitoring can determine the average blood pressure level and the short- and long-term blood pressure variability (circadian rhythm). The circadian blood pressure rhythm appears to be mediated mainly by the circadian rhythm of the sympathetic tone which is linked to changes in physical and mental activity, e.g. the waking-sleeping cycle. A statistically significant circadian blood pressure rhythm was observed in approximately 80% of mild to moderate essential hypertensive patients as well as in normal subjects. However, in patients with Cushing's syndrome, under glucocorticoid treatment, or with hyperthyroidism, central and/or peripheral autonomic dysfunction (Shy-Drager syndrome, spinal cord injury, brainstem lesions, diabetic neuropathy, uremic neuropathy, etc), chronic renal failure, eclampsia, malignant hypertension, sleep apnea syndrome or systemic atherosclerosis, the normal circadian blood pressure rhythm appears to be eliminated or reversed, while in those with primary aldosteronism, renovascular hypertension, pheochromocytoma without paroxysmal hypertension, diabetes insipidus, acromegaly, hyperparathyroidism or hyperprolactinemia, the nocturnal blood pressure fall has been observed as in normal subjects. The alteration in the circadian blood pressure rhythm was observed with different pathophysiological conditions, although no specific pattern was observed for any condition. A disturbance in any part of the hierarchy of factors that regulate the circadian rhythm of sympathetic neural tone seems to disturb the circadian blood pressure rhythm. We conclude that ambulatory blood pressure monitoring is not critically important in the diagnosis of secondary hypertension although it does help in screening for secondary hypertension.