disease has major feature Headache brain disorder headache disorder headaches, chronic headache, intractable UMLS:C0393735 headache disorder chronic daily headaches daily headaches, chronic MEDGEN:140743 SCTID:230461009 headaches, chronic daily headache, chronic headache, chronic daily intractable headaches chronic headaches MONDO:0021146 syndrome, headache chronic daily headache headaches, intractable headache syndrome cephalgia syndrome intractable headache Various conditions with the symptom of headache. Headache disorders are classified into major groups, such as primary headache disorders (based on characteristics of their headache symptoms) and secondary headache disorders (based on their etiologies). (International Classification of Headache Disorders, 2nd ed. Cephalalgia 2004: suppl 1) MESH:D020773 headache syndromes cephalgia syndromes chronic headache daily headache, chronic EFO:0009550 neurological pain disorder