Novelty seeking and introversion do not predict the long-term risk of Parkinson disease

Abstract

Objective: It has been suggested that people who develop Parkinson disease (PD) may have a characteristic premorbid personality. We tested this hypothesis using a large historical cohort study with long follow-up.

Methods: We conducted a historical cohort study in the region including the 120-mile radius centered in Rochester, MN. We recruited 7,216 subjects who completed the Minnesota Multiphasic Personality Inventory (MMPI) for research at the Mayo Clinic from 1962 through 1965 and we considered 5 MMPI scales to measure sensation seeking, hypomania, positive emotionality, social introversion, and constraint. A total of 6,822 subjects (94.5% of the baseline sample) were followed over 4 decades either actively (via interview and examination) or passively (via medical records).

Results: During follow-up, 227 subjects developed parkinsonism (156 developed PD). The 3 MMPI scales that we selected to measure the extroverted personality construct (sensation seeking, hypomania, and positive emotionality) did not show the expected pattern of higher scores associated with reduced risk of PD. Similarly, the 2 MMPI scales that we selected to measure the introverted personality construct (social introversion and constraint) did not show the expected pattern of higher scores associated with increased risk of PD. However, higher scores for constraint were associated with an increased risk of all types of parkinsonism pooled together (hazard ratio 1.39; 95% CI 1.06-1.84; p = 0.02).

Conclusions: We suggest that personality traits related to introversion and extroversion do not predict the risk of PD.

Figure 1 Flow chart of study cohort *Of these 4,415 subjects, 4,309 (97.6%) resided within and 106 (2.4%) resided outside of the 5-state region at the time of the follow-up interview. Of the 106 subjects who resided outside of the 5-state region, 33 screened positive for parkinsonism, 32 of them were alive, and 7 were examined. **Of these 1,489 subjects, 1,211 (81.3%) had both medical record and death certificate information, 34 (2.3%) only medical record information, 231 (15.5%) only death certificate information, and the remaining 13 (0.9%) had neither. MMPI = Minnesota Multiphasic Personality Inventory.

Figure 2 Hazard ratios (HRs) for Parkinson disease for 5 Minnesota Multiphasic Personality Inventory (MMPI) personality scales stratified by age at time of MMPI completion (A) The 3 scales measuring the extroverted personality construct yielded higher HRs when measured earlier in life. However, only the trend for the hypomania scale was significant. (B) By contrast, the 2 scales measuring the introverted personality construct yielded higher HRs when measured later in life. However, the trends were not significant. HRs and 95% confidence interval bars were staggered to improve the graphic display.