Table 1.

Summary of research studies

Author	N (sample)	Measures/Variables	Outcomes
Dick, Eccleston and Crombez (2002)[10]	FM=20 RA=20 MSK=20 And 20 pain-free controls	Attentional functioning: selective attention, sustained attention, attentional switching, and auditory-verbal working memory	Pain patients had impaired cognitive functioning on an ecological sensitive neuropsychological test of everyday attention.
			Attentional deficits in the patients’ group were significant on tasks of selective and sustained attention and auditory-verball working memory.
			FM patients showed a significantly higher level of anxiety than the other 3 groups.
Dick and Rashiq (2007)[12]	24 participants	Pain, pain catastrophizing, attentional functioning	2/3 of participants with chronic pain had found impaired on attentional task and they had significantly greater difficulties in maintaining a memory trace during a challenging test of working memory.
Shin, Katz, Wallhagen and Julian (2012)[26]	115 subjects	Cognitive function (verbal learning, short delay, immediate delay, long delay recall, inhibition, switching condition) and covariates (sociodemographic and disease characteristics), blood test, depression	Proportion of persons who were classified as cognitively impaired on each test ranged from 8-29%.
			More than 20% of subjects were found to be cognitively impaired in executive function (28% on the design fluency test and 21% on the trail making test).29% and 18% of subjects were cognitively impaired in visuospatiall learning and verbal learning/memory, respectively.
Shin, Julian and Katz (2013)[23]	122 subjects	Cognitive function: verbal learning, short delay, immediate delay, and long delay recall, executive functioning, inhibition, switching conditions, and depression Physical function: functional limitation, functional disability	Nearly one-third of subjects were classified as cognitively impaired on 4 or more out of 16 subtests. About 20-30% of subjects were found to be cognitively impaired in executive function; specifically, 29% in the nonverbal fluency test and 21% in the sequencing and set-shifting test. 20% and 29% of subjects were impaired in verbal learning/memory and visuospatial learning/memory, respectively.
Melo and Silva (2012)[27]	FM=13 RA=13 SLE=11 (age range=30 to 80 years)	Memory, language, executive function	FM and SLE group showed significantly higher means of the neuropsychiatric symptoms of anxiety, irritability, and hallucinations than the RA group in the neuropsychiatric inventory. Young adults performed better in all tests as compared with the elderly.
Bilgici, Terzi, Guz and Kuro (2014)[15]	FM=16 RA=15 Health controls=15	cognitive performance (global attention/working memory, language, visual and verbal memory, visuospatial process and executive function)	FM and RA patients performed poorly on most cognitive measurements compared with healthy controls and much similar to each other in performance except for the executive functions. No significant differences were found between FM and RA patients on the attention, memory, word fluency and visuospatial tasks. RA and FM patients performed poorly on verbal memory tests when compared with control groups.
Simos et al. (2016)[21]	100 consecutive RA patients aged 28-67 years (90% woman)	Verbal short- term and working memory, verbal episodic memory, executive function (set-shifting and verbal fluency), visuomotor processing speed, Premorbid verbal capacity, premorbid nonverbal ability, nonverbal reasoning and problem-solving ability, pain severity, anxiety and depression	20% of RA patients were cognitively impaired. Deficient performances were noted on tests of verbal short-term memory, immediate and short-delay verbal episodic recall, verbal working memory and phonemic fluency. Pain severity and anxiety and depression symptomatology jointly accounted for a small (not significant) proportions of variance in each of the cognitive indices measured in the study.
Gunnarsson, Grahn, Agerstrom (2016)[16]	3 pain groups: acute pain (n=38), regularly recurrent pain (n=58), persistent pain (n=54) and healthy control group (n=51)	Sustained attention, cognitive control, psychomotor ability	Patients with persistent pain showed significantly worse on sustained attention and psychomotor ability compared with healthy controls. The acute pain group showed a significant decrement in psychomotor ability and regularly current pain group showed a decrement in sustained attention.

MSK: Musculoskeletal, SLE: Systemic Lupus Erythematosus, FM: Fibromyalgia, RA: Rheumatoid Arthritis