Saúl post: Hold your horses: Are you telling me that MS can cause impulsivity?!

Neuropsychiatric disorders and cognitive impairment have a negative impact on daily functioning and quality of life of MSers. While much research has focused on comorbid depression in pwMS, less attention has been given to the association between MS and impulsive behaviour. 

Impulsiveness is a multidimensional construct of behavioral aspects including response disinhibition, propensity to act without concern for consequences, increased tendency to anticipate reward and enhanced exploration of novel and intense experiences. It is unclear whether or not individuals with MS have higher levels of impulsivity than the general population; however, it is possible that cognitive and executive dysfunction in MSers might lead to disinhibition or impulsive acts.

Our MS research group, led by Dr Toro, performed a study to address this gap in the literature. We compared the levels of impulsivity between MS patients and subjects without MS using the Barratt Impulsiveness Scale version 11 (BIS–11) and the Immediate and Delayed Memory Tasks (IMT-DMT), which are among the most commonly used and reliable instruments for the assessment of impulsivity. Our results showed that pwMS had higher levels of cognitive impulsivity than healthy subjects. We could not account for all potential confounding factors such as irritability, attention impairment and working memory dysfunction; however, objective measures for impulsiveness further supported our findings.

Another recent study has also shown that MSers attempt to compensate for their impulsivity with increased neural activity in several brain regions that are typically required for response inhibition in healthy subjects: fusiform gyrus, cingulate gyrus, cerebellum and putamen. However, this compensatory process is not sufficient.

This is a relatively new field of study; therefore further studies should be conducted by other groups to reproduce our results before considering impulsivity as part of the spectrum of psychological disorders in MS.

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Toro J, Blanco L, Orozco-Cabal LF, Díaz C, Reyes S, Burbano L, et al. Impulsivity Traits in Patients with Multiple Sclerosis. Mult Scler Relat Disord 2018;22:148-152

BACKGROUND: Multiple sclerosis (MS) is a demyelinating disease with a lifetime prevalence of 4.41/100000 in Bogota, Colombia. It is known that it can be related with neuropsychiatric disorders, increasing by a factor of three the prevalence of depression in MS patients compared to general population. However, less attention has been given to the association between MS and impulsive behavior.

METHODS: This cross-sectional study compared the levels of impulsivity controlling for the presence of MS. 60 patients with MS and 60 sex- and age-matched subjects without MS were included. In order to assess depression and impulsivity, participants completed the 13-item short form of the Beck Depression Inventory (BDI-SF), the self-report Barratt Impulsiveness Scale version 11 (BIS-11) and the Immediate and Delayed Memory Tasks (IMT-DMT) as an objective measure of impulsive behavior.

RESULTS: Total scores, motor and cognitive subscales on the BIS-11 were significantly higher in the MS group. However, median BDI-SF score was also higher in MS patients than in subjects without MS (p < 0.001). To rule out depression as a confounding factor, stratification was performed using the BDI-SF score. In the subgroup of individuals with a BDI-SF< 8, the BIS-11 cognitive subscale scores were significantly higher in patients with MS than in subjects without MS (p = 0.041). In the IMT/DMT test, subjects with MS had a fewer number of correct detections than did subjects without MS, after controlling for BDI-SF score (p = 0.0001/p = 0.003). The ratio of commission errors to correct detections in the IMT was significantly higher in the MS group (p = 0.011).

CONCLUSION: Patients with MS showed higher levels of cognitive impulsivity than subjects without MS. Objective measures for impulsiveness further support this finding. Impulsiveness scales scores might be biased by depression, which should be considered when assessing impulsivity in MS.
Saúl Reyes