The Frequent Unusual Headache Syndromes: A Proposed Classification Based on Lifetime Prevalence.
BACKGROUND
There is no agreement on a single cutoff point or prevalence for regarding a given disease as rare. The concept of what is a rare headache disorder is even less clear and the spectrum from a very frequent, frequent, occasional to rare headache syndrome is yet to be established.


OBJECTIVE
An attempt has been made to estimate the lifetime prevalence of each of the headache subtypes classified in the ICHD-II.


METHODS
Using the ICHD-II, 199 different headache subtypes were identified. The following classification was made according to the estimated lifetime prevalence of each headache disorder: very frequent (prevalence >10%); frequent (between 1 and 10%); occasional (between 0.07 and 1%); and unusual or rare (<0.07%).


RESULTS
One hundred and fifty-four of 199 (77%) were categorized as unusual headache disorders, 7/199 (4%) as very frequent, 9/199 (5%) as frequent, and 29/199 (15%) as occasional forms of headache disorder.


CONCLUSIONS
The unusual headache syndromes do not appear to be as infrequent in clinical practice as has been generally believed. About three-fourths of the classified headache disorders found in the ICHD-II can be considered as rare. This narrative review article may be regarded as an introduction to the concept of unusual headaches and a proposed classification of all headaches (at least those listed in the ICHD-II).
Department of Neuropsychiatry, Neurology and Neurosurgery Unit, Federal University of Pernambuco, Brazil.|Neurology and Neurosurgery Unit, Hospital Esperança, Brazil.
Marcelo M
MM
Valença
Department of Neuropsychiatry, Neurology and Neurosurgery Unit, Federal University of Pernambuco, Brazil.
Daniella A
DA
de Oliveira
D005260:Female; D006261:Headache / Q000145:classification* / Q000453:epidemiology*; D006801:Humans; D038801:International Classification of Diseases; D008297:Male; D015995:Prevalence; D039781:PubMed / Q000706:statistics & numerical data
classification; lifetime prevalence; orphan disease; rare disease; unusual headache