Secondary hypertension

Secondary hypertension is hypertension due to an underlying cause. It accounts for 10% of hypertension cases.

Secondary hypertension should be suspected in:

• Younger patients (<40) with hypertension
• Severe hypertension
• Treatment-resistant hypertension

Etiology

• Common
  • Obstructive sleep apnoea (OSA)
  • Renal parenchymal disease
  • Renal vascular disease (renal artery stenosis)
    • Atherosclerotic renovascular disease
    • Fibromuscular dysplasia
  • Primary hyperaldosteronism (Conn syndrome)
• Rare
  • Phaeochromocytoma
  • Cushing syndrome
  • Thyroid disease (hypo or hyper)

Pathomechanism

The mechanism by which these causes cause secondary hypertension depends on the cause. Some activate RAAS, some activate the sympathetic system, some cause fluid and salt retention, and some function by other mechanisms.

Clinical features

• OSA -> daytime sleepiness, snoring, obesity, non-dipping of BP on ABPM
• Renal parenchymal disease -> abnormal kidney function
• Renovascular hypertension -> abdominal bruit, worsening kidney function after taking RAAS inhibitor, asymmetrical kidney size
  • Atherosclerotic renovascular disease -> other features of atherosclerosis
  • Fibromuscular dysplasia -> younger women
• Primary aldosteronism -> mostly asymptomatic, some are hypokalaemic

Diagnosis and evaluation

Depends on the suspected cause of the secondary hypertension. Doppler ultrasound for renovascular disease, polysomnography for OSA, etc.

Treatment

The hypertension itself must be treated, usually with multiple drugs, to prevent complications. The underlying disease should be treated, if possible.