Does the cognitive index of the symptom severity scale (SSS) evaluate cognition? Data from subjective and objective cognitive measures in fibromyalgia.

OBJECTIVES: The current provisional diagnostic criteria for the fibromyalgia syndrome (FM) include a cognitive index score (SSS-Cog), which constitutes a part of the Symptom Severity Scale (SSS). The current study aimed at assessing the validity of the cognitive index score, by comparing this subjective measure of cognitive impairment with an objective measure of cognitive functioning, collected through comprehensive computerised cognitive testing and assessment.

METHODS: 50 FM patients underwent a computerised cognitive assessment battery, including testing in domains of memory, executive function, attention and information processing speed (NeuroTraxCorp.). Age and education standardised scores were computed. 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-II).

RESULTS: The index score for subjective assessment of cognitive decline (SSS-Cog) was not correlated with any of the objective cognitive measures. However, a positive correlation was found between the SSS-Cog and the FIQ, the WPI and the VAS measures, all reflecting subjective overall functional ability.

CONCLUSIONS: No significant relationship was found between FM patients' subjective appraisal of cognitive deficit and objective cognitive scores on all computerised subtests. However, subjective appraisal of cognitive impairment was found to be strongly and significantly related to patients' functional ability. Therefore, we suggest reconsidering the definition of this index score (SSS-Cog) and propose developing novel and more accurately defined tools in order to measure cognitive impairment in FM patients, for both diagnostic and epidemiological purposes.