How Well Do Essential Tremor Patients Report Whether or Not They Have Parkinson's Disease? Validity of Self-report Data from a Large Cohort Study.

Background/objective: In clinical and research studies in which one is dealing with essential tremor (ET) patients, the identification of related conditions, such as Parkinson's disease (PD), is important. A reasonable starting point is to directly ask the patient about their disease status. We are not aware of studies on the validity of ET patients' self-reports of PD (i.e., ETPD). Our aim was to assess the validity of a self-report of PD in this setting.

Methods: ET cases were enrolled in a prospective study. At each visit, they were asked, "Have you been diagnosed with Parkinson's disease?", a videotaped neurological examination was performed, and PD diagnoses (i.e., ETPD) were assigned by a senior movement disorders neurologist.

Results: 291 ET cases underwent 899 study evaluations. Seven cases were diagnosed with ETPD. Summing data across all cases and all study evaluations, sensitivity = 56.3% and specificity = 98.1%. The positive predictive value of a report of PD was low (36.0%), whereas the negative predictive value of a report of no PD was high (99.2%).

Conclusions: Screening, in general, can be a difficult process, but in the setting of ET and PD, the issues are particularly challenging. Our overarching goal is to fill a gap in knowledge and inform clinical researchers and treating physicians who are working with tremor populations. Although some information is garnered from asking ET patients whether they have been diagnosed with ETPD, the low sensitivity and low positive predictive values indicate that the value of self-reported PD diagnoses is limited.