Abstract

Background: Several diagnostic criteria for major depressive disorder (MDE) overlap with those of Chronic Fatigue Syndrome (CFS). Furthermore, atypical MDE (A-MDE), a subtype of MDE characterised by profound fatigue and which has frequently been linked with CFS, exhibits similar low cortisol levels to CFS. However, this result has been only found in specimens designed for measuring acute cortisol levels. In this study, we measure cortisol levels in subjects with CFS and in subjects with A-MDE, without psychiatric comorbidity, using both hair and saliva specimens, to gain a measure of both short and long-term cortisol levels in these two conditions. Methods: Hair cortisol concentration, representing the cortisol concentration of the previous three months, and salivary cortisol, measured at six time-points across one day and including the cortisol awakening response (CAR), post-awakening delta cortisol and the total daily output, were assessed in an age and gender matched group of 34 controls, 15 subjects with A-MDE and 17 with CFS. Results: CFS (mean 92.2 nmol/l.h, s.d. 33.2 nmol/l.h) and A-MDE (mean 89.1 nmol/l.h, s.d. 22.6 nmol/l.h) subjects both showed lower cortisol total daily output in saliva (AUCg) in comparison to healthy controls (mean 125.5 nmol/l.h, s.d. 40.6 nmol/l.h). However, hair cortisol concentration was not lower than that of controls in either patient group. CFS and A-MDE did not differ from one another on any cortisol measures. CFS subjects reported fewer daily hassles and less severe psychic anxiety symptoms in comparison to A-MDE subjects (all p < 0.05). However, they did not differ in the severity of somatic anxiety symptoms. There was also no difference in the presence of overlapping symptoms such as fatigability and concentration/memory problems between A-MDE and CFS subjects. Conclusion: Low levels of cortisol found using short-term measures of daily output may be transient, since cortisol levels were normal when a long-term measure (hair) was studied. This might be explained by a potential cortisol rhythm alteration. Although these disorders have their distinctive depressive and somatic features, they may from part of a wider group of Somatic Symptom Disorders (SSD), given the findings of the same pattern of cortisol secretion in both disorders and increased frequency of overlapping clinical features.