title: The prevalence and characteristic features of cyclicity and variability in Cushing's disease.
abstract: OBJECTIVE
  Cyclical Cushing's syndrome may render the diagnosis and management of Cushing's disease difficult. The aim of the present study was to investigate the prevalence of cyclicity and variability in patients with Cushing's disease, and to identify putative distinctive features.
  
  
  METHODS
  Retrospective case-note study.
  
  
  METHODS
  We analysed the case records of 201 patients with Cushing's disease in a retrospective case-note study. Cyclicity was considered as the presence of at least one cycle, defined as a clinical and/or biochemical hypercortisolaemic peak followed by clinical and biochemical remission, followed by a new clinical and/or biochemical hypercortisolaemic peak. The fluctuations of mean serum cortisol levels, as assessed by a 5-point cortisol day curve, defined the variability.
  
  
  RESULTS
  Thirty (14.9%; 26 females) patients had evidence of cyclicity/variability. 'Cycling' patients were older but no difference in sex or paediatric distribution was revealed between 'cycling' and 'non-cycling' patients. The median number of cycles was two for each patient, and 4 years was the median intercyclic period. A trend to lower cure rate post-neurosurgery and lower adenoma identification was observed in 'cycling' compared with 'non-cycling' patients. In multivariate analysis, older patients, longer follow-up, female sex and no histological identification of the adenoma were associated with an increased risk of cyclic disease.
  
  
  CONCLUSIONS
  This large population study reveals that cyclicity/variability is not an infrequent phenomenon in patients with Cushing's disease, with a minimum prevalence of 15%. Physicians should be alert since it can lead to frequent problems in diagnosis and management, and no specific features can be used as markers.
authors.affiliation: Department of Endocrinology, St Bartholomew's Hospital, London EC1A 7BE, UK.
authors.forename: Krystallenia I
authors.initials: KI
authors.lastname: Alexandraki
authors.forename: Gregory A
authors.initials: GA
authors.lastname: Kaltsas
authors.forename: Andrea M
authors.initials: AM
authors.lastname: Isidori
authors.forename: Scott A
authors.initials: SA
authors.lastname: Akker
authors.forename: William M
authors.initials: WM
authors.lastname: Drake
authors.forename: Shern L
authors.initials: SL
authors.lastname: Chew
authors.forename: John P
authors.initials: JP
authors.lastname: Monson
authors.forename: G Michael
authors.initials: GM
authors.lastname: Besser
authors.forename: Ashley B
authors.initials: AB
authors.lastname: Grossman
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D005260:Female; D006801:Humans; D006854:Hydrocortisone / Q000097:blood; D008297:Male; D008875:Middle Aged; D047748:Pituitary ACTH Hypersecretion / Q000453:epidemiology*; D015995:Prevalence; D012189:Retrospective Studies; D013997:Time Factors; D055815:Young Adult
chemical_list: D006854:Hydrocortisone