Poorer Cognitive Performance in Patients with Essential Tremor-Parkinson’s Disease vs. Patients with Parkinson’s Disease

Abstract

BackgroundPatients with essential tremor (ET) seem to be at increased risk of developing Parkinson’s disease (PD). Surprisingly, little has been written about this clinical entity, ET-PD. Cognitive dysfunction is a well-known feature of PD, and can also be an issue in patients with ET. Whether the presence of the combined diagnosis, ET-PD, is associated with additive cognitive effects as compared with PD has not been studied.MethodsThirty ET-PD patients and 53 age-matched PD patients were enrolled in a clinical-epidemiological study. Two cognitive screens, the Telephone Interview for Cognitive Status (TICS, score = 0–41) and Folstein Mini-Mental State Examination (MMSE; range 0–30), were administered.ResultsThe MMSE score was lower in ET-PD than PD [26.5 ± 3.1 (median 28.0) vs. 28.4 ± 2.2 (median 29.0), p = 0.001]. The TICS score was lower in ET-PD than PD [31.7 ± 3.9 (32.0) vs. 35.0 ± 2.0 (35.0), p < 0.001]. Subscores of these tests that related to orientation (p < 0.001), language (p < 0.001), and working memory (p = 0.001) were lower in ET-PD than PD, whereas the delayed memory subscore was only marginally lower in ET-PD than PD (p = 0.06), and the two groups did not differ with respect to the motor/construction subscore (p = 0.22). Both global cognitive scores were inversely correlated with disease duration (for MMSE score, Spearman’s r = −0.46, p < 0.001; for TICS score, Spearman’s r = −0.53, p < 0.001).ConclusionThe combined diagnosis, ET-PD, seemed to be associated with additive cognitive effects as compared with PD alone.

Awareness of cognitive impairment in individuals with essential tremor

“…Examples of cognitive deficits found in ET include problems in memory, executive functioning, visuospatial skills, verbal fluency, and attention 2, 3, 35 . The etiology of these deficits has yet to be clearly determined.…”

“…It is also possible that cognitive changes in ET reflect a co-morbid degenerative condition. Indeed, there is evidence that individuals with ET are at increased risk of co-morbid neurodegenerative disorders, such as Parkinson’s disease 3 Alzheimer’s disease and progressive supranuclear palsy (PSP) 35, 38 . Awareness may deteriorate in ET patients with cognitive impairment as a result of compromise to brain regions that are critical for supporting self-evaluation, and which may be directly or indirectly affected by ET pathology or co-occurring pathologies.…”

“…Physicians may also benefit from conducting neuropsychological screening whether or not the patient has cognitive complaints to improve the early detection of dementia 47 . The need for cognitive screening is also underscored by the likely heterogeneous etiology of cognitive deficits in ET, as specific cognitive profiles may require have different prognoses 3 .…”

“…On average, compared to age-matched controls, individuals with ET exhibit a range of cognitive deficits and are at increased risk for mild cognitive impairment (MCI) 2 and dementia 3, 4 . The extent to which patients with ET who develop clinically significant cognitive impairment accurately perceive their cognitive changes is not known.…”

Essential tremor-Parkinson's disease: A double whammy

“…That is, the combined condition is associated with broader (i.e., non-motor) effects and clinical features aside from the tremor appear to be additive. In a prior study of the same cohort [29], we showed that Folstein Mini-mental state scores were lower in ET-PD than PD; however, we did not explore sleep or motor features that differentiated the two groups, nor did we compare them to a group of ET cases.…”