Objective: To estimate the frequency and correlates of involuntary emotional expression disorder (IEED) in Parkinson's disease (PD) using the Center for Neurologic Study-Lability Scale (CNS-LS) and recently-proposed diagnostic criteria for IEED.
Background: IEED is characterized by uncontrollable emotional episodes, typically unrelated to or in excess of the underlying mood, and occurring with minimal or no stimulus. IEED has been reported to occur in many neurological disorders and neurodegenerative diseases, but its prevalence and correlates in PD have not been well studied. Additionally, there is no published research using recently-proposed IEED diagnostic criteria in any population.
Methods: 193 patients with idiopathic PD were assessed with a neuropsychiatric battery, including the CNS-LS and the 15-item Geriatric Depression Scale (GDS-15). A subset (N=100) was also administered a diagnostic interview by a blinded rater that applied criteria for both IEED and Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR) depressive disorders.
Results: Applying formal diagnostic criteria, 7.0% of patients were diagnosed with IEED, and an additional 7.0% had subsyndromal IEED symptoms. Applying recommended CNS-LS cutoff scores from other populations, either 42.5% (cutoff > or =13) or 16.6% (cutoff > or =17) screened positive for IEED. Depressive symptoms were associated with higher CNS-LS scores (B[SE]=0.27[.08], P=.001) but not with a diagnosis of IEED (odds ratio=1.1, [95% CI=1.0-1.3], P=.16). The CNS-LS had poor discriminant validity for an IEED diagnosis (AUC=.79, no cutoff value with sensitivity and specificity both >60%).
Conclusions: IEED and depression are overlapping but distinct disorders in PD. IEED symptoms may occur in up to 15% of PD patients, but a disorder occurs in only half of those, suggesting that often IEED symptoms are not clinically significant in this population. The CNS-LS does not appear to be a good screening instrument for IEED in PD, in part due to its high correlation with depressive symptoms.