Theory of Mind (ToM), the ability to attribute mental states to others, is an integral domain of social cognition essential to human interaction. While cognitive decline is well known to be a common and early feature of MS, research into social cognitive impairment in MS patients is scarcer. In recent years, MS has been shown to affect ToM even in the absence of impairment in other cognitive domains.
We aimed to define the predictive value of social cognition tests to discriminate MS patients from Healthy Controls (HC), compare them with other standard neuropsychological tests, and determine the optimal cut-off points for scoring.
Sixty consecutive MS patients and 60 HC were enrolled, matched by sex, age, and education level. All participants were assessed with a standard neuropsychological battery for MS (MACFIMS), with cognitive impairment defined as a defect in two or more domains. All participants also underwent social cognition testing [Reading the Mind in the Eyes test (RMET) and Videos test (VT)].
Discriminatory power of each test was determined by Receiver Operating Characteristics curve analysis, calculating the area under the curve (AUC).
As expected, HC outperformed MS patients in all cognitive domains, and 34 (56.7%) patients were classified as cognitively impaired. Compared to HC, patients had significantly lower scores on ToM testing (RMET 58.7% ± 13.8% vs 81.9% ± 10.4%, p < 0.001 and VT 75.3% ± 9.3% vs 88.1% ± 7.1%, p < 0.001). Interestingly, performance on ToM tests did not differ significantly between cognitively impaired and cognitively intact patients (RMET 56.9± 14.5% vs. 61.0± 12.7%, p=0.251 and VT 74.5± 11.2% vs. 76.3±5.9%, p=0.431).
ROC analysis yielded the highest discriminatory power for ET (AUC 0,923, 95% CI 0,859 to 0,964, p<0.001), followed by VT (AUC 0.879, 95% CI 0.807 to 0.931, p<0.001). Among standard neuropsychological tests, Symbol digit modalities test had the highest discriminatory power (AUC 0.729, 95% CI 0.640 to 0.806, p<0.001).
Youden index analysis established the optimal cutoff point at =<27 for ET (S 93.33, E 75.00, Youden index J 0.6833) and =<21 for VT (S 76.67, E 88.33, Youden index J 0.65).
As has been previously reported, in our patient series, ToM deficit was shown to occur independently of cognitive decline. Furthermore, ToM tests showed higher discriminatory power for the diagnosis of MS than standard neuropsychological assessment. Thus, social cognitive impairment might merit further investigation as a possivle clinical marker of disease in MS,