title: Chronic daily headache: identification of factors associated with induction and transformation.
abstract: BACKGROUND
  Chronic daily headache (CDH) is one of the more frequently encountered headache syndromes at major tertiary care centers. The analysis of factors related to the transformation from episodic to chronic migraine (CM) and to the de novo development of new daily persistent headache (NDPH) remain poorly understood.
  
  
  OBJECTIVE
  To identify somatic factors and lifestyle factors associated with the development of CM and NDPH.
  
  
  METHODS
  We used a randomized case-control design to study the following groups: 1) CM with analgesic overuse (ARH), n = 399; 2) CM without analgesic overuse, n = 158; and 3) NDPH, n = 69. These groups were compared with two control groups: 1) episodic migraine, n = 100; and 2) chronic posttraumatic headache (CPTH); n = 65. Associated medical conditions were assessed. We investigated the case groups for any association with somatic or behavioral factors. Data were analyzed by the two-sided Fischer's exact test, with the odds ratio being calculated considering a 95% confidence interval using the approximation of Woolf.
  
  
  RESULTS
  When the active groups were compared with the episodic migraine group, the following associations were found: 1) ARH: hypertension and daily consumption of caffeine; 2) CM: allergies, asthma, hypothyroidism, hypertension, and daily consumption of caffeine; and 3) NDPH: allergies, asthma, hypothyroidism, and consumption of alcohol more than three times per week. The following associations were found when comparing the active groups with CPTH: 1) ARH: asthma and hypertension; 2) CM: allergies, asthma, hypothyroidism, hypertension, and daily consumption of caffeine; and 3) NDPH: allergies, asthma, hypothyroidism, and consumption of alcohol more than three times per week.
  
  
  CONCLUSIONS
  Several strong correlations were obtained between patients with specific types of CDH and certain somatic conditions or behaviors; some have not been previously described. Transformation of previously episodic headache or development of a NDPH thus may be related to certain medical conditions and behaviors beyond the frequently incriminated precipitant analgesic overuse. As similar results were obtained when CPTH was used as a control, the correlation is more complex than simple comorbidity.
authors.affiliation: Department of Neurology and Epidemiology, Albert Einstein College of Medicine, Bronx, New York, USA.
authors.forename: Marcelo E
authors.initials: ME
authors.lastname: Bigal
authors.forename: Fred D
authors.initials: FD
authors.lastname: Sheftell
authors.forename: Alan M
authors.initials: AM
authors.lastname: Rapoport
authors.forename: Stewart J
authors.initials: SJ
authors.lastname: Tepper
authors.forename: Richard B
authors.initials: RB
authors.lastname: Lipton
mesh_terms: D000328:Adult; D000700:Analgesics / Q000009:adverse effects / Q000627:therapeutic use; D002110:Caffeine / Q000009:adverse effects; D016022:Case-Control Studies; D002908:Chronic Disease; D005260:Female; D020773:Headache Disorders / Q000150:complications / Q000209:etiology*; D006801:Humans; D006973:Hypertension / Q000150:complications; D007037:Hypothyroidism / Q000150:complications; D008297:Male; D008881:Migraine Disorders / Q000150:complications / Q000209:etiology*; D013577:Syndrome
chemical_list: D000700:Analgesics; D002110:Caffeine