Self-awareness of executive dysfunction in Huntington's disease: Comparison with Parkinson's disease and cervical dystonia

Authors


Correspondence: Emilia Sitek, MA, PhD, Department of Neurology, St Adalbert Hospital, Jana Pawla II 50, 80-462 Gdansk, Poland. Email: emsitek@gmail.com

Abstract

This study assessed self-awareness of executive deficits in patients with Huntington's disease (HD) in comparison to patients with Parkinson's disease (PD) and with cervical dystonia (CD). Eighty-nine patient–proxy pairs participated in the study (23 with HD, 25 with advanced PD, 21 with mild PD and 20 with CD). Executive function was assessed with the Stroop test and the Dysexecutive Questionnaire. Insight into executive impairment in HD is mildly affected, when compared to PD and CD.

PATIENTS WITH HUNTINGTON'S disease (HD) present with anosognosia for executive deficits.[1, 2] Nonetheless, it remains unknown if these problems are of clinical relevance when compared to Parkinson's disease (PD), in which executive–frontal abnormalities are also present, but insight into executive problems seems relatively preserved.[3]

Recently, we found that anosognosia for motor symptoms is greater in HD than in PD and cervical dystonia (CD).[4] Here, we test the hypothesis that similar group differences also emerge for self-awareness of executive deficits.

Methods

After signing informed consent, 89 HD, advanced PD (aPD), mild PD (mPD), and CD patient–proxy pairs, whose recruitment details have been previously described,[4] participated in the study (Table 1). Study procedures were approved by the local bioethics committee.

Table 1. Patient characteristics and patient–proxy ratings of executive function (mean ± SD)
 

HD

n = 23

aPD

n = 25

mPD

n = 21

CD

n = 20

H/F/χ2 test

Intergroup differences

(P < 0.05)a

  1. aIn case of one-way analysis of variance Tukey post-hoc test was used. aPD, advanced Parkinson's disease; CD, cervical dystonia; DEX, Dysexecutive Questionnaire; HD, Huntington's disease; MADRS, Montgomery Asberg Depression Rating Scale; MMSE, Mini-Mental State Examination; mPD, mild Parkinson's disease; UHDRS, Unified Huntington's Disease Rating Scale.
Demographics
Age (years)49.83 ± 11.1265.68 ± 10.3064.67 ± 7.5951.75 ± 12.98

F(3,85) = 14.11

P < 0.001

HD, CD<aPD, mPD
Education (years)12.50 ± 2.0912.48 ± 3.6012.55 ± 3.7013.25 ± 4.48

H(3, n = 89) = 1.99

P = 0.57

M:F14:912:1315:68:12χ2 = 4.92; P = 0.18
Duration of disease (years)7.35 ± 5.0612.16 ± 4.504.33 ± 2.568.35 ± 5.72H(3, n = 89) = 28.76; P < 0.0001aPD>HD, mPD
UHDRS motor score38.09 ± 14.33
MMSE26.10 ± 2.6326.50 ± 1.8527.75 ± 2.3828 ± 1.62H(3,n = 89) = 14.48; P = 0.02HD, aPD<mPD
MADRS13.04 ± 8.4615.04 ± 6.967.90 ± 5.7211.65 ± 6.72H(3, n = 89) = 11.47; P = 0.0094aPD>mPD
Stroop: trial III – trial I (s)48.82 ± 36.8181.54 ± 76.3629.57 ± 14.5135.65 ± 18.11

H(3, n = 87) = 22.64

P < 0.0001

aPD>mPD, CD
Stroop: proportion of errors to reactions in trial III0.20 ± 0.190.19 ± 0.180.04 ± 0.070.03 ± 0.03

H(3, n = 87) = 31.81

P < 0.0001

HD, aPD>mPD, CD
DEX: patient ratings31.70 ± 14.5034.68 ± 8.9723.48 ± 10.6428.40 ± 9.20

H(3, n = 89) = 12.76

P = 0.005

aPD>mPD
DEX: proxy ratings35.04 ± 11.4327.08 ± 10.9426.38 ± 15.2122.35 ± 13.94

H(3, n = 89) = 11.06

P = 0.01

HD>CD
DEX: patient–proxy difference–3.35 ± 18.797.60 ± 12.73–2.90 ± 21.096.05 ± 14.55

F(3,85) = 2.62

P = 0.06

DEX: total underestimation score13.83 ± 10.186.00 ± 5.6912.24 ± 14.686.00 ± 7.78

H(3, n = 89) = 11.18

P = 0.0108

HD>CD

General cognition and mood were assessed with Mini-Mental State Examination (MMSE)[5] and the Montgomery–Asberg Depression Rating Scale (MADRS),[6] respectively.

The Dysexecutive Questionnaire (DEX) was independently applied to patients and their proxies to rate patients' executive impairment. DEX is a 20-item questionnaire, used in previous studies of HD[2] and PD.[3] It addresses four aspects of executive function: emotions/personality; motivation; behavior; and cognition. Each item is scored from 0 to 4, with higher scores indicating more severe executive deficits. There are two versions of DEX: a self-rated version and the proxy version.[5] In this study, for each patient–proxy pair the patient–proxy difference was analyzed for each item separately, providing a patient–proxy difference score. Subsequently, a total underestimation score was computed solely on the basis of items for which the patient provided a lower rating than the caregiver (indicating lower severity of a given symptom). Such differences were summed to obtain an underestimation score for each patient–caregiver pair. The underestimation score, as previously described, shows if the patient–proxy discrepancy is the effect of the underestimation, overestimation or an unspecific discrepancy (inconsequent ratings of one's function as better or worse than seen by others).[7]

The Stroop task was used with a modified procedure.[4] The proportion of errors to reactions in the interference trial constituted the cognitive control measure. Additionally, difference in time to complete trial III and trial I was computed to measure mental tracking speed.

The HD patients were additionally assessed with the Unified Huntington's Disease Rating Scale (UHDRS; Motor, Independence Scale).[5]

Statistical analysis

The between-group differences were tested using one-way analysis of variance or H Kruskal–Wallis test, with post-hoc comparisons depending on the data distribution. Correlation analyses were performed using Spearman rank correlation.

Results

Executive impairment

The HD group performed significantly worse than the mPD and CD patients on the cognitive control score of the Stroop task (Table 1), but the HD patients did not differ from the aPD group. Further, mental tracking speed was significantly lower only in the aPD group in comparison to the mPD and CD groups.

Patient–proxy discrepancies on the assessment of executive impairment

According to the patient ratings, the aPD group presented with more dysexecutive symptoms than the mPD group. In contrast, proxy ratings had a significantly higher rate of dysexecutive symptoms only in HD when compared to CD, but no differences between aPD and mPD. The total underestimation score was the highest in the HD group. The DEX patient–proxy difference was not significant.

Correlates of the underestimation of symptoms in HD

No associations among the total underestimation score in the HD group and the MADRS, Stroop, MMSE, UHDRS scores, or disease duration, were identified.

Discussion

This study partially confirms previous reports on deficient self-awareness of executive dysfunction in HD.[1, 2] Patient objective test performance showing executive problems in HD and aPD was consistent with proxy ratings but not with patient ratings, indicating reduced insight in HD. Further, HD patients underestimated their executive deficits in comparison to CD patients. The severity of anosognosia of executive impairment in HD seems to be mild, because the simple difference score regarding patient–proxy ratings was not statistically significant, and the underestimation score did not differentiate HD from PD. Interestingly, when compared to aPD, mPD patients also tended to underestimate their deficits. Nonetheless, this effect, which may be related to more depressive symptoms in aPD than in mPD, was not statistically significant. In the HD there was no relationship between insight and mood.

By showing that defective awareness of executive problems is greater in HD than in aPD having comparable cognitive status, this is the first study documenting differences in self-awareness of executive dysfunction between these movement disorders.

The mechanism for the reduced insight into executive deficits in HD patients remains unclear. Impaired self-awareness in HD is frequently associated with prefrontal abnormalities.[1, 4] Thus, it is likely that the orbitofrontal–limbic pathology in HD[8] may explain the present results. Nonetheless, without neuroimaging data this hypothesis could not be tested.

Conclusion

Self-awareness of executive impairment in HD seems to be mildly affected when HD patients are compared to individuals with PD and CD.

Acknowledgments

There are no conflicts of interest. EJS was supported by the START Scholarship from the Foundation for Polish Science. EJS and MH received scholarships from the Polish Ministry of Science and Higher Education.

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