This comment, published in the Journal of the Royal Society of Medicine in May 1990, was written in response to a letter by Dr. Lev. You can read the letter here: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1292388/
We read the letter from Lev (November 1989 JRSM, p 693) with interest, but see a danger in using assumptions as to aetiology in definition of study groups. Operational definitions not making this assumption will produce replicable findings and progress towards better definitions and understanding of aetiology.
Definitions of depressed control groups are difficult, for example the following need to be controlled:
(1) Demographic variables
(2) Severity of depression symptoms: inappropriate control groups for ME patients would be severely depressed inpatients. Outpatient depressives are not too dissimilar in severity.
(3) Psychotropic medication: this is less likely to be given to ME patients where treatment is not agreed and could modify symptoms to be compared.
(4) Psychiatric history: in possible ME patients a previous significant psychiatric illness prior to fatigue symptoms leads to difficulty in studying this symptom and produces too much overlap with depressed controls.
(5) History of febrile illness: to minimize overlap, one must also control for preceding febrile illness in otherwise typical depressive illness.
Comparison of control groups should be serial, not cross-sectional as physical symptoms and markers may fluctuate, as may fatigue and depression.
Assessment of depressive symptoms is difficult, as Lev points out, due to non-specific ‘biological’ symptoms of depression. However, psychic ones such as pessimism should not overlap and could be assessed.
The concept of fatigue is poorly understood, as is its assessment. The paradigm of pain research has much to offer, where ‘dichotomization’ of physical and psychological components is not thought useful, but assessment emphasizes all components of the experience of pain. Thus, psychometric assessment of fatigue, for example, its severity, frequency, and pattern may be a future research area. Using such a paradigm, our initial findings of differences in fatigue in the two groups are because depressed patients are predominantly anergic, but ‘ME’ patients have more variability and unpredictable onset of fatigue relative to the severity of exercise attempted. Lack of motivation overlaps in both groups, explicable in Lev’s own terms as due to a reaction to a chronic illness.
~SEAN LYNCH Lecturer and Honorary Senior Registrar in Psychiatry
~RAM SETH Senior Registrar in Psychiatry St Charles Hospital, London
Source: S Lynch and R Seth. Depression and myalgic encephalomyelitis. J R Soc Med. 1990 May; 83(5): 341. PMCID: PMC1292666. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1292666/pdf/jrsocmed00136-0073a.pdf