Similar to regular migraines — perhaps a unilateral, throbbing component, maybe nausea and/or photophobia & phonophobia. But since it occurs every day or almost every day, it lacks the main component of a migraine diagnosis, viz. cyclic recurrences. The key issue — if anything about a patient’s chronic headache reminds us of migraine, maybe a trial of migraine prophylaxis would help.
See posting Recurrent Headaches for general discussion of migraines.