Tag: heterogeneity

Reducing heterogeneity in chronic fatigue syndrome: a comparison with depression and multiple sclerosis

Abstract:

Chronic fatigue syndrome (CFS) is a heterogeneous illness characterized by a high prevalence of psychiatric problems. We reasoned that we could reduce heterogeneity by excluding patients with psychiatric problems preceding CFS.

We compared the functional status, mood, fatigue level, and psychiatric status of this more homogeneous group of CFS patients with the same parameters in patients with mild multiple sclerosis and in patients with major depression or dysthymia.

Patients with CFS and those with multiple sclerosis were similar in terms of level of anger, severity of depression, level of anxiety, and frequency of current psychiatric diagnoses. Patients with CFS resembled depressed patients in having impaired vigor and experiencing substantial fatigue and confusion–problems constituting part of the case definition of CFS.

The group with CFS was not psychologically vulnerable before the development of this condition and maintained adequate networks of social support despite disabling illness.

Stratification to exclude patients with prior psychiatric disease and those with mild CFS allowed us to define a group of patients with CFS who more resembled patients with mild MS than patients with major depression or dysthymia and thus were more likely to have illness with an infectious or immunologic cause. Use of such a stratification strategy should prove important in testing of the viral/immunologic hypothesis of the etiology of CFS.

 

Source: Natelson BH, Johnson SK, DeLuca J, Sisto S, Ellis SP, Hill N, Bergen MT. Reducing heterogeneity in chronic fatigue syndrome: a comparison with depression and multiple sclerosis. Clin Infect Dis. 1995 Nov;21(5):1204-10. http://www.ncbi.nlm.nih.gov/pubmed/8589144

 

Can the chronic fatigue syndrome be defined by distinct clinical features?

Abstract:

To determine whether patients diagnosed as having chronic fatigue syndrome (CFS) constitute a clinically homogeneous class, multivariate statistical analyses were used to derive symptom patterns and potential patient subclasses in 565 patients. The notion that patients currently diagnosed as having CFS constitute a single homogeneous class was rejected.

An alternative set of clinical subgroups was derived. The validity of these subgroups was assessed by sociodemographic, psychiatric, immunological and illness behaviour variables. A two-class statistical solution was considered most coherent, with patients from the smaller class (27% of the sample) having clinical characteristics suggestive of somatoform disorders. The larger class (73% of sample) presented a more limited combination of fatigue and neuropsychological symptoms, and only moderate disability but remained heterogeneous clinically. The two patient groups differed with regard to duration of illness, spontaneous recovery, severity of current psychological morbidity, utilization of medical services and CD8 T cell subset counts. The distribution of symptoms among patients was not unimodal, supporting the notion that differences between the proposed subclasses were not due simply to differences in symptom severity.

This study demonstrated clinical heterogeneity among patients currently diagnosed as CFS, suggesting aetiological heterogeneity. In the absence of discriminative clinical features, current consensus criteria do not necessarily reduce the heterogeneity of patients recruited to CFS research studies.

 

Source: Hickie I, Lloyd A, Hadzi-Pavlovic D, Parker G, Bird K, Wakefield D. Can the chronic fatigue syndrome be defined by distinct clinical features? Psychol Med. 1995 Sep;25(5):925-35. http://www.ncbi.nlm.nih.gov/pubmed/8588011

 

Exercise responses and psychiatric disorder in chronic fatigue syndrome

Comment in: Exercise responses in the chronic fatigue syndrome. Objective assessment of study is difficult without knowledge of data. [BMJ. 1995]

 

Fatigue, exercise intolerance, and myalgia are cardinal symptoms of the chronic fatigue syndrome, but whether they reflect neuromuscular dysfunction or are a manifestation of depression or other psychiatric or psychological disorders diagnosed in a high proportion of fatigued patients in the community is unclear.’ In previous studies patients with the chronic fatigue syndrome showed exercise intolerance in incremental exercise tests, which seemed to be related to an increased perception of effort; also, blood lactate concentrations in some patients tended to increase more rapidly than normal at low work rates, implying inefficient aerobic muscle metabolism.2 We examined venous blood lactate responses to exercise at a work rate below the anaerobic threshold in relation to psychiatric disorder.

You can read the rest of this article here: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2550606/pdf/bmj00607-0028.pdf

 

Source: Lane RJ, Burgess AP, Flint J, Riccio M, Archard LC. Exercise responses and psychiatric disorder in chronic fatigue syndrome. BMJ. 1995 Aug 26;311(7004):544-5. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2550606/pdf/bmj00607-0028.pdf

 

Seasonal symptom variation in patients with chronic fatigue: comparison with major mood disorders

Abstract:

The psychobiology of idiopathic fatigue has received renewed interest in the medical literature in recent years. In order to examine the relation between chronic, idiopathic fatigue and specific subtypes of depressive illness, we characterized the pattern and severity of seasonal symptom variation in 73 patients with chronic, idiopathic fatigue, compared to patients with major depression (n = 55), atypical depression (n = 35), and seasonal affective disorder (n = 16) Fifty of the fatigued subjects also met the specific Centers for Disease Control and Prevention case criteria for chronic fatigue syndrome, though this definition was unable to discriminate a distinct subgroup of patients, based on their seasonality scores alone. As a group, the fatigued subjects reported the lowest levels of symptom seasonality of any of the study groups. Further, even in those fatigued subjects with scores in the range of those seen in patients with seasonal affective disorder, seasonality was not reported to be a subjectively distressing problem. These findings lend support to the idea that although chronic fatigue shares some clinical features with certain mood disorders, they are not the same illnesses. These data are also consistent with the emerging view that chronic fatigue represents a heterogeneously determined clinical condition.

 

Source: Zubieta JK, Engleberg NC, Yargiç LI, Pande AC, Demitrack MA. Seasonal symptom variation in patients with chronic fatigue: comparison with major mood disorders. J Psychiatr Res. 1994 Jan-Feb;28(1):13-22. http://www.ncbi.nlm.nih.gov/pubmed/8064638

 

Chronic fatigue syndrome and heterogeneity

Comment on: The measurement of fatigue and chronic fatigue syndrome. [J R Soc Med. 1992]

 

One thing which hampers medical research is a frustrating tendency for researchers to conclude that heterogeneous groups are homogeneous. Several examples can be cited including research into sudden infant death syndrome. In his editorial on chronic fatigue syndrome (CFS) Wessely (April 1992 JRSM, p 189) asserts that previous views suggesting CFS to be simply a form of somatized depression are no longer tenable because of one published and one unpublished study showing biological differences from major depression. This view is just as untenable as the notion that all CFS is depression. Surely the most likely explanation is that CFS represents a heterogeneous group. The notion that one or two positive findings exclude all other explanations is a dangerous one. Aside from the fact that it negates the possibility of heterogeneity it may have a tendency to narrow thinking on the subject, and this is, after all, the food for medical research.

You can read the full comment here: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1293669/pdf/jrsocmed00107-0092a.pdf

 

Source: Wright B. Chronic fatigue syndrome and heterogeneity. J R Soc Med. 1992 Sep;85(9):588. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1293669/