Chronic Migraine

Chronic migraine is headache on 15 or more days each month for over 3 months, with migraine features on at least 8 of those days. It causes major disability, and medication overuse is present in about half of patients.

The prevalence is about 1 to 2% in the general population. About 2.5% of people with episodic migraine progress to chronic migraine each year. It is more common in women and in the fourth decade.

Risk factors for progression. High attack frequency, medication overuse, obesity, depression and anxiety, sleep disorders, high caffeine intake, snoring, previous head or neck injury and low socioeconomic status.

Comorbidity. Depression, anxiety, insomnia, chronic pain, cardiovascular disease and irritable bowel syndrome.

Pathophysiology.

Repeated attacks lead to central sensitisation of trigeminovascular and brainstem circuits, with altered cortical excitability and impaired descending pain inhibition.

Calcitonin gene related peptide drives neurogenic inflammation and sensitisation, and acute drug overuse lowers the threshold for attacks.

• Daily or near daily headache with unilateral or bilateral pulsating pain, moderate to severe intensity, nausea, photophobia and phonophobia.
• Episodes of full migraine on at least 8 days each month, between milder tension type days.
• Aura in some patients; allodynia and neck pain are common.
• Medication overuse headache: simple analgesics on 15 or more days or triptans, opioids, ergots or combination analgesics on 10 or more days each month.

Red flags.

• New or changed headache over age 50, thunderclap onset or progressive pattern.
• Systemic symptoms (fever, weight loss), neurological deficits, papilloedema or seizures.
• Headache triggered by exertion or Valsalva, or associated with pregnancy.

• Diagnosis is clinical using the ICHD-3 criteria, supported by a headache diary kept for at least 1 month, recording days, severity, drug use and triggers.
• Neuroimaging (MRI) for red flags or a changed pattern; no routine imaging for typical migraine with a normal examination.
• Blood tests only when secondary causes are suspected: ESR, CRP over age 50, thyroid function.
• Screen for depression, anxiety, sleep disorders and medication overuse.

Differential diagnosis. Chronic tension type headache, medication overuse headache, new daily persistent headache, hemicrania continua, cervicogenic headache, idiopathic intracranial hypertension, secondary headache and sleep apnoea headache.

• Withdraw the overused acute drug and limit acute treatment to under 10 days each month for triptans and under 15 days each month for simple analgesics; explain that headache may worsen for 1 to 2 weeks before improving.
• Modify lifestyle: regular sleep, meals, hydration and exercise; reduce caffeine; treat obesity, sleep apnoea and mood disorders.
• Sumatriptan for acute attacks: 50 mg orally at onset, increased to 100 mg if needed; repeat after 2 hours if the headache returns. Maximum 300 mg in 24 hours, and limit use to under 10 days each month. Monitor blood pressure and chest symptoms. Contraindicated in ischaemic heart disease, uncontrolled hypertension, previous stroke or TIA, hemiplegic or brainstem aura, severe hepatic impairment (maximum 50 mg in mild to moderate impairment) and with ergots or monoamine oxidase inhibitors; acceptable in pregnancy when needed.
• Preventive drugs (review at 3 months):
• Topiramate 25 mg orally at night for 1 week, increased by 25 mg weekly in 2 divided doses to 100 mg daily. Maximum 200 mg daily. Review at 3 months and stop if there is no benefit. Monitor bicarbonate, mood, weight, kidney stones and visual symptoms. Halve the dose when creatinine clearance is under 70 mL/min; contraindicated in pregnancy (oral clefts) and effective contraception is needed.
• Propranolol modified release 80 mg orally once daily, increased after 2 to 4 weeks to 160 mg daily. Maximum 240 mg daily. Review at 3 months. Monitor heart rate and blood pressure. Avoid in asthma, bradycardia, heart block, hypotension and peripheral vascular disease; reduce dose in hepatic impairment; use caution in pregnancy.
• Amitriptyline 10 mg orally at night, increased by 10 mg every 1 to 2 weeks as tolerated to 30 to 50 mg at night. Maximum 75 mg at night. Review at 6 to 8 weeks. Monitor sedation, anticholinergic effects, postural hypotension and mood; baseline ECG over age 40 or with cardiac risk. Avoid after recent myocardial infarction, with arrhythmia, in angle closure glaucoma or urinary retention; cap at 50 mg in older adults; reduce dose in hepatic impairment.
• OnabotulinumtoxinA 155 units intramuscularly across 31 head and neck sites every 12 weeks (up to 195 units with additional sites). Maximum 195 units each session. Assess after 2 to 3 cycles and stop if monthly headache days fall by under 30%, or if migraine reverts to episodic for 3 months. Monitor for ptosis, neck weakness and injection site reactions. Avoid with infection at injection sites and neuromuscular disease; avoid in pregnancy unless benefit outweighs risk.
• Erenumab 70 mg subcutaneously once monthly, increased to 140 mg monthly if needed. Maximum 140 mg monthly. Review at 3 months. Monitor blood pressure, constipation and injection reactions. No renal or hepatic adjustment; use caution in cardiovascular disease and Raynaud phenomenon; avoid in pregnancy unless benefit outweighs risk.
• Fremanezumab 225 mg subcutaneously once monthly, or 675 mg every 3 months. Maximum 225 mg monthly or 675 mg quarterly. Review at 3 months. Monitor hypersensitivity and blood pressure. No renal or hepatic adjustment; avoid in pregnancy unless benefit outweighs risk.
• Galcanezumab 240 mg subcutaneously as a loading dose, then 120 mg monthly. Maximum 120 mg monthly after the loading dose. Review at 3 months. Monitor hypersensitivity and constipation. No renal or hepatic adjustment; avoid in pregnancy unless benefit outweighs risk.
• Non-drug treatment: cognitive behavioural therapy, relaxation and neuromodulation.

Monitoring. Review at 4 to 6 weeks and 3 months using the diary; reassess every 6 to 12 months, and consider a drug holiday after 6 to 12 months of good control.

Referral and escalation. Headache specialist for failure of 3 preventive drugs; urgent review for red flags.

Special groups. Women: avoid oestrogen containing contraception with aura, and plan pregnancy (topiramate and valproate avoided). Older adults: lower doses and screen for secondary causes.