Table 1. The SNOOP4 list of ‘red flags’ for secondary headaches8.

	Mnemonic	Examples of red flags	Possible secondary headache
S	Systemic symptoms	Fever, weight loss	Meningitis, encephalitis, giant cell arteritis
	Secondary risk factor	Malignancy, immunosuppression	Metastasis, leptomeningeal carcinomatosis
N	Neurological deficit	Focal neurological sign, altered conscious state	Stroke, space-occupying lesion, hydrocephalus
O	Onset	Thunderclap, abrupt onset	Includes subarachnoid haemorrhage, pituitary apoplexy, cerebral venous sinus thrombosis
O	Older age	New or progressive headache (>50 years)	Mass lesion, giant cell arteritis
P4	Positional	Changes with change in posture	Intracranial hypotension or hypertension
	Pattern change	Change in character from baseline	Mass lesion
	Precipitated by	Valsalva, coughing, sneezing	Posterior fossa lesion
	Papilloedema	Visual obscuration	Idiopathic intracranial hypertension