Dear Editor,
M.A. Taylor and M. Fink have responded to the WFSBP Task Force report on depression stating that the group has only briefly commented on the hypothalamic-pituitary-adrenal perturbations that have been identified in depressive illness and did not assess the literature on sleep EEG1.
We are, of course, aware of Caroll's finding2 3 that “abnormal cortisol metabolism” was found among severely depressed patients who met ICD criteria for “melancholic depression” and that “the Dexamethasone Suppression Test (DST) has been recommended as a specific marker of melancholia”. However, while the reliability and specificity of the DST is 70% for melancholic depression, this applies only for a clinically pre-diagnosed and defined subgroup of patients, namely those with melancholia. Clearly if abnormal DST response is taken as marker for “depression” its specificity and reliability will be substantially lower. A marker that is used and reliable only for a prediagnosed subgroup of depressed patients is, to our minds, of limited utility. In our report we did discuss the DST in terms of its value as a biological marker in “the majority of depressives” and we think our conclusions about its limitations in this respect are reasonable.
Our realistic, (we hope not pessimistic) view is a consensus and does not reflect that the interests or expertise of any particular participant.
Getting clear evidence for specificity and reliability of the sleep EEG as a biological marker is very difficult. Prolonged rather than short REM latencies have been reported in a subgroup of depression. Reduced sleep quality is extremely unspecific. Therefore the marker is too weak.
Finally our report on biological markers in depression follows the consensus criteria as published by the Biomarkers Definitions Working Group4, in which a parameter is only defined as marker when it fulfils selectivity and specificity, and is related to a pathomechanism of the disease. Unfortunately the DST lacks diagnostic specificity being abnormal in psychosis in general, anorexia nervosa and Alzheimer's disease, as well as depression. Also, the sleep EEG does not fulfil the consensus criteria for biological markers although it might be a useful research tool. Sincerely yours P.F. Riederer, Germany on behalf of the WFSBP-Task Force authors of the article “Biological markers in depression” (World J Biol Psychiatry 2007;8:141–174): Mössner R, Mikova O, Koutsilieri E, Saoud M, Ehlis A-C, Müller N, Fallgatter A, and the members of the Task Force on Biological Markers (Jablenski A, Youdim MBH, Cowen P, Matsuoka H, Murphy DL, Saiz Ruiz J, Schalling M, Thome J)