430 J Neurol Neurosurg Psychiatry 1998;64:430 J Neurol Neurosurg Psychiatry: first published as 10.1136/jnnp.64.4.430 on 1 April 1998. Downloaded from

EDITORIAL COMMENTARY

The importance of mental fatigue

The paper by Christodoulou et al in this issue of the Jour- assessment of cognitive impairment may be an underesti- nal (pp 431–4) draws attention to memory deficits in some mate of actual dysfunction experienced in everyday life. patients with operationally defined chronic fatigue syn- Recent randomised controlled trials of cognitive behav- drome, and days of (enforced) physical inactivity. Many ioural therapy (graded activity and cognitive restructuring) studies have assessed cognitive dysfunction in patients with show it to be superior to relaxation therapy in the treatment chronic fatigue. The earliest reported superior abilities in of functional impairment and fatigue in patients with such patients against controls or age matched normal sub- chronic fatigue syndrome, independent of mood change. jects, probably reflecting a biased selection of cases from The fatigue scale used in one such study3 includes several higher socioeconomic groups. Later studies have been the items of cognitive fatigue and these showed the same subject of at least two major reviews.12 improvement as the more physical items (S Wessely, Patients with chronic fatigue syndrome do not have clear personal communication) in response to a cognitive evidence of either general intellectual decline, sensory behavioural therapy programme which did not include deficits (assessed using evoked potentials), or perceptual specific neurocognitive remediation. Hence the subtle but impairments. Reaction times have, not surprisingly, been definite cognitive impairment in chronic fatigue syndrome found to be slower. Deficits do emerge in patients attempt- documented in the current study seems to be part and par- ing complex tasks involving eVortful processing or divided cel of the disorder. Some authors have tended to place attention. Some studies which did not find memory deficits undue weight on the neuro prefix to neuropsychological in patients with chronic fatigue syndrome, nevertheless tests, overinterpreting poor scores as indicative of showed them to be more susceptible to interference and, neurological damage or brain disease. Clearly, such curiously, not helped by cueing. Despite most studies find- interpretation is premature (see Cope et al4). The problem ing little objective evidence of cognitive dysfunction, of direction of causality is also relevant as inactivity itself patients with chronic fatigue syndrome complain of more may reduce alertness and cognitive speed. The treatment impairment than normal or depressed controls. This studies highlight this by showing that increased activity subjective cognitive impairment has been found to be leads to improved general cognition. strongly related to fatigue, anxiety, and severity of Cognitive impairment is a strong predictor of functional depressed mood. deficits in conditions as varied as Alzheimer’s disease and Depression and anxiety are common in patients with schizophrenia. On the strength of this study the same can chronic fatigue syndrome and cognitive dysfunction (espe- now be said of chronic fatigue syndrome. As such the paper cially impairment in short term memory and information serves to bring chronic fatigue further into the mainstream processing) has been reported in patients with aVective of neuropsychiatric disorders and underscores the disabil- disorders. The current study took careful steps to try to ity which often accompanies the syndrome. http://jnnp.bmj.com/ exclude depression as a cause of functional impairment MICHELLE V LAMBERT and did so using both a diagnostic interview and a self ANTHONY DAVID reported questionnaire. It is still possible that some Section of Neuropsychiatry, Kings’ College School of Medicine and patients with chronic fatigue syndrome, especially those Dentistry and the Institute of Psychiatry, London SE5 8AF,UK attending specialist clinics, may have minimised their psy- chological symptoms for fear of being told that their fatigue 1 Wearden AJ, Appleby L. Research on cognitive complaints and cognitive was “all in the mind” or because of strong beliefs about the functioning in patients with chronic fatigue syndrome (CFS): what conclu- sions can we draw? 1996; :197–211. J Psychosom Res 41 on September 27, 2021 by guest. Protected copyright. non-psychiatric status of the syndrome. Nevertheless the 2 Moss-Morris R, Petrie KJ, Large RG, et al. Neuropsychological deficits in implication that there is a direct relation between mental chronic fatigue syndrome: artifact or reality? J Neurol Neurosurg Psychiatry 1996;60:474–7. and physical fatigue is supported by this study. 3 Deale A, Chalder T, Marks I, et al. Cognitive behavior therapy for chronic Christodoulou et al found that patients who failed more fatigue syndrome: a randomised controlled trial. Am J Psychiatry 1997154: 408–14. tests of cognitive function (especially those assessing verbal 4 Cope H, Pernet A, Kendall B, et al. Cognitive functioning and magnetic memory) reported more days of inactivity. The laboratory resonance imaging in chronic fatigue. Br J Psychiatry 1995;167:86–94.