Etiology and Pathogenesis of Hypertension
Approximately 90% of cases of hypertension are primary (essential), in which the etiology is unknown, and 10% are secondary to identifiable causes. Primary hypertension most likely results from a dysregulation of various renal, hormonal, and cellular processes in conjunction with environmental factors such as diet and exercise. These processes include abnormal sodium transport, increased sympathetic nervous system activity, abnormal vasodilation, excess transforming growth factors β (TGF-βs), and abnormalities in the renin-angiotensin-aldosterone system (Fig 3-1).
Causes of secondary hypertension vary. Following are some of these causes, along with signs associated with secondary hypertension:
polycystic kidney disease: flank mass
renovascular disease: unilateral abdominal bruit in a young patient with marked hypertension; new-onset hypertension with severe end-organ disease
pheochromocytoma: markedly labile BP with tachycardia and headache
hyperaldosteronism: persistent hypokalemia in the absence of diuretic therapy or marked drop with low-dose diuretics
coarctation of the aorta: delayed or absent femoral pulses in a young patient
Cushing syndrome: truncal obesity and abdominal striae
Secondary causes of hypertension should be suspected in persons who have accelerating hypertension or hypertension unresponsive to medication or in those who have a sudden change in previously well-controlled BP. Patients with secondary hypertension are more likely to have resistant hypertension, which is defined as a failure to achieve goal BP even when the patient adheres to the optimal doses of 3 antihypertensive drugs, including a diuretic. The prevalence of resistant hypertension is currently not known, but indirect population study evidence suggests it is more common than previously suspected. This prevalence may be secondary to an aging population, and the increased prevalence of obesity, diabetes mellitus, obstructive sleep apnea syndrome, and chronic kidney disease.
Most cases of diagnosed resistant hypertension are due to inadequate dosing of medication and patient nonadherence to treatment. The most common factors contributing to resistant hypertension are excess sodium intake, volume overload, and failure to treat the condition, whether with dietary modification or the proper diuretic and dosage. Other causes of secondary hypertension and resistant hypertension are listed in Table 3-2.
Figure 3-1 Renin-angiotensin-aldosterone system.
Table 3-2 Causes of Secondary Hypertension and Resistant Hypertension
Excerpted from BCSC 2020-2021 series: Section 1 - Update on General Medicine. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.