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IHS Diagnosis ICD-10
10.3.3 Headache attributed to hypertensive encephalopathy [I67.4] G44.813  

Diagnostic criteria:

  1. Headache with at least one of the following characteristics and fulfilling criteria C and D:
    1. diffuse pain
    2. pulsating quality
    3. aggravated by physical activity
  2. Persistent blood pressure elevation to >160/100 mm Hg with at least two of the following:
    1. confusion
    2. reduced level of consciousness
    3. visual disturbances (other than those of typical migraine aura) including blindness
    4. seizures
  3. Headache develops in close temporal relation to blood pressure elevation
  4. Headache resolves within 3 months after effective treatment and control of hypertension
  5. Other causes of the neurological symptoms have been excluded

Comments:

Hypertensive encephalopathy is thought to occur when compensatory cerebrovascular vasoconstriction can no longer prevent cerebral hyperperfusion as blood pressure rises. As normal cerebral autoregulation of blood flow is overwhelmed, endothelial permeability increases and cerebral oedema occurs. On MRI, this is often most prominent in the parieto-occipital white matter.

Although hypertensive encephalopathy in patients with chronic arterial hypertension is usually accompanied by a diastolic blood pressure of >120 mm Hg, and by grade 3 or 4 hypertensive retinopathy (Keith-Wagner classification), previously normotensive individuals may develop signs of encephalopathy with blood pressures as low as 160/100. Hypertensive retinopathy may not be present at the time of clinical presentation.

Any cause of hypertension, including phaeochromocytoma and ingestion of vasopressor toxins, can lead to hypertensive encephalopathy.