Diagnostic Approach to Unilateral Headache When Standing Up

Primary Diagnosis: Spontaneous Intracranial Hypotension

The American Academy of Neurology suggests that spontaneous intracranial hypotension (SIH) should be considered when a patient presents with a one-sided headache that develops upon standing, characterized by an orthostatic pattern 1, 2.
SIH presents with orthostatic headache that can be unilateral or bilateral, with a characteristic pattern of being absent or only mild (1-3/10 severity) upon waking or after prolonged lying flat, onset within 2 hours of becoming upright, improvement by >50% within 2 hours of lying flat, and consistent timing of onset and offset 1, 2.
The headache may also present as an "end of the day" or "second half of the day" pattern with improvement when lying flat 1, 2.

Nausea and vomiting can be associated with SIH 3.
Hearing changes (muffled hearing, tinnitus) and visual disturbances can also occur 4.
Dizziness is another symptom that may be present 5.

Orthostatic hypotension is distinguished by a documented blood pressure drop of ≥20 mmHg systolic or ≥10 mmHg diastolic upon standing, and confirmed through formal standing tests with hemodynamic monitoring 1, 2.
Postural tachycardia syndrome (PoTS) is characterized by a heart rate increase >30 bpm within 10 minutes of standing, and symptoms of orthostatic intolerance 7, 1, 2.
Cervicogenic headache is differentiated by being provoked by cervical movement rather than posture, reduced cervical range of motion, and associated myofascial tenderness 1, 2.
Migraine is distinguished by being provoked by movement rather than posture, and having migrainous features such as throbbing quality, photophobia, and phonophobia 1, 2.

A detailed history should document the precise orthostatic pattern, including severity when lying flat vs. standing, time to onset after standing, time to improvement after lying flat, and consistency of this pattern 1, 2, 4.
Physical examination should include vital signs, complete neurological examination, fundoscopy, and cervical spine range of motion and palpation 1, 2, 3.
A formal standing test should be performed if orthostatic hypotension or PoTS is suspected, measuring blood pressure and heart rate supine and at 1, 3, 5, and 10 minutes of standing 1, 2, 4.
Neuroimaging, such as brain MRI, may be needed if SIH is suspected based on orthostatic headache pattern 1, 2.

Refer to neurology within 2-4 weeks if the patient can care for themselves, or within 48 hours if they cannot care for themselves but have help, or emergency admission if they cannot care for themselves and lack help 1, 2.