Cognitive functioning in fibromyalgia: The central role of effort

Highlights

• Patients suffering from fibromyalgia typically report significant difficulty with memory and concentration (“Fibrofog”)

• A computerized cognitive battery demonstrated impairments of memory, attention and processing speed in fibromyalgia patients

• Performance was significantly affected among patients demonstrating low levels of effort during cognitive testing

• Assessing effort should be incorporated into standard measures for assessing cognitive performance in fibromyalgia

Abstract

Objective

Fibromyalgia syndrome (FM) patients demonstrate deficits in tests of attention, executive functioning and verbal memory. We assessed the role of effort in the cognitive impairment in FM patients, alongside common symptoms of pain, fatigue and depression.

Method

50 FM patients underwent a computerized cognitive assessment battery including memory, executive function, attention and information processing speed (NeuroTrax Corp.). Age and education standardized scores were computed. Effort was assessed by the Test of Memory Malingering (TOMM). FM symptoms were assessed by the Fibromyalgia Impact Questionnaire (FIQ), Widespread Pain Index (WPI) and Symptom Severity Scale (SSS), a Visual Analog Scale (VAS) of clinical pain and the Beck Depression Inventory (BDI-2).

Results

FM patients showed impaired performance on the memory, attention and information processing speed domains. According to the TOMM, sub-optimal effort was shown by 16% of patients. TOMM scores were not associated with pain, fatigue or depression. After controlling for effort, no significant impairment was found in memory scores; however attention and information processing speed scores remained significantly low. Multiple regressions analysis, performed in order to evaluate the contribution of effort, pain, fatigue and depression, found effort to be the only significant variable accounting for variance of cognitive scores on all domains.

Conclusion

The findings confirm impaired attention and processing speed in FM patients, independent of effort level. Nonetheless, the findings point to a general and strong effect of effort on neuropsychological performance in FM patients, especially in the domain of memory, emphasizes the importance of effort testing in this population.

Introduction

Fibromyalgia (FM) is a condition characterized by chronic widespread pain and fatigue, associated with numerous other symptoms attributable to the central nervous system, including disrupted sleep and cognitive impairment. Many patients also demonstrate comorbid symptoms of anxiety and depression, while others appear to remain remarkably resilient in face of the chronic symptoms [1].

Due to the array of symptoms the patients encounter, FM is associated with a considerable impairment of quality of life as well as social and functional activity [2]. The etiology and pathogenesis of FM remain incompletely understood, although significant progress has been made. Chronic widespread pain, the predominant symptom of FM, is currently ascribed to a condition variously referred to as “central sensitization” [3], [4] and more recently as “pain centralization” [5]. These overlapping terms refer to pain which is the end-product of amplification within the central nervous system, rather than originating from peripheral pathology or pain- generators. Nonetheless, while pain is the hallmark of FM, cognitive impairment, particularly memory and concentration, often referred to by patients as “fibro fog”, are among the most common symptoms encountered in the clinical setting [6], [7]. Notably these symptoms are extremely disruptive and distressing for patients, who may report feeling more functionally incapacitated by dis-cognition than by pain. However, despite the subjective burden levied upon FM patients by cognitive symptoms, several studies assessing objective measures of cognition have actually found FM patients to perform similarly to healthy controls. Thus on standard neuropsychological tests [8], [9] as well as on specific tests of verbal memory [10], [11], visual memory [12], short term memory storage [13] and attention [14], [15], FM patients have been reported to score similar to healthy controls. While these surprising results may be explained by under-powered studies or by looking at the wrong targets, one of the more interesting interpretations relates to the phenomenon of FM patients “rising to the occasion”, i.e. mustering increased effort on a short run basis in order to perform adequately on a given test. This concept is supported at least to some extent by neuro-imaging results which demonstrate that FM patients use more brain resources in order to achieve the same task [16]. On the other hand, as recently reviewed by Kravitz and Katz [17], FM patients have been shown to under-perform on a number of neuro-cognitive scales, including episodic and semantic memory, executive function, working memory and attention. The American College of Rheumatology (ACR) has recognized the importance of these cognitive impairments for FM by incorporating them into the currently suggested diagnostic criteria for FM [18].

The impact of various components of the clinical spectrum of FM on cognitive performance, including depression, fatigue and pain has previously been studied [12], [19], [20]. Recently, growing research interest has been focused on measuring the effect of effort on cognitive performance. While measuring effort has classically been associated with identifying malingering, little attention has been paid to the possibility that decreased effort may reflect the increased fatigability of the subject, or in other words the limited resources which the individual may feel they have in order to complete the assignment. In the current study we have attempted to evaluate the effect of effort on the cognitive performance of FM patients, while controlling for the effect of FM-related symptoms such as pain, fatigue and depression.

In order to achieve this purpose, we have chosen to use the TOMM, a test widely implemented for assessing effort on neuropsychological testing. The TOMM is not affected by age, education and cognitive impairment, except in severe dementia due to Alzheimer's disease. It is also not affected by pain and depression, factors specifically relevant for the FM population, as recently demonstrated [21]. For the purpose of cognitive testing we have chosen to use the NeuroTraxTM computerized cognitive assessment battery, which is a well validated, standardized and extensive test, allowing rapid and efficient evaluation of a broad spectrum of cognitive function, including memory, attention, executive function and processing speed, all of which have previously been documented to be affected in FM. For evaluation the clinical severity of FM symptoms we have chosen to use the Widespread Pain Index (WPI) and the Symptom Severity Score (SSS), both components of the current suggested ACR diagnostic criteria for FM [18], [22] which are also widely used for quantitative assessment of FM symptomology; we have also utilized the Fibromyalgia Impact Questionnaire (FIQ), a standard functional tool used in the literature [23].