[Fooled by the diurnal rhythm].
BACKGROUND
Under ordinary circumstances, the daily secretion of cortisol displays a characteristic diurnal variation with a peak in the morning and a trough at night. It is important to understand the variation in cortisol secretion when analysing results of cortisol tests.


METHODS
We present a patient in whom work-up for acute headache revealed a pathologically low morning serum cortisol level. This led to further evaluation of adrenocortical function with an adrenocorticotropic hormone (ACTH) stimulation test and cortisol day profiles in serum and saliva.


CONCLUSIONS
The analyses showed normal adrenocortical function and diurnal variation with normal amplitudes. The morning rise in cortisol secretion was, however, delayed by 7-8 hours due to a delayed sleep phase. This case illustrates the importance of the diurnal rhythm in the assessment of pituitary-adrenal function. There should be clinical suspicion of a disorder before a test is requested.
Løvås
Kristian
K
Medisinsk avdeling, Haukeland Universitetssykehus, Bergen. kristian.lovas@helse-bergen.no
Cooper
John Graham
JG
Thorsen
Thor
T
Thordarson
Hrafnkell
H
Husebye
Eystein S
ES
D000324:Adrenocorticotropic Hormone; D000328:Adult; D002940:Circadian Rhythm / Q000502:physiology*; D003937:Diagnosis, Differential; D006261:Headache / Q000097:blood / Q000209:etiology / Q000503:physiopathology; D006801:Humans; D006854:Hydrocortisone / Q000097:blood / Q000378:metabolism*; D008297:Male; D010913:Pituitary-Adrenal System / Q000502:physiology; D012463:Saliva / Q000737:chemistry
D000324:Adrenocorticotropic Hormone; D006854:Hydrocortisone